# Sierra Sound and capacitors



## Doug Bowman (Jan 8, 2008)

I would like to replace the batteries on my Sierra Sound and Phoenix Sound systems with capacitors. Since the existing batteries are no more than 9 volts. I will assume that I don't need capacitors rated at more than that. 
Questions: 
Am I correct in my assumption? 
How much capacity do I need? 
Is 10 Farad enough capacity to replace the battery for the startup and shut down sounds?
Can I use my existing battery charger to keep the capacitor charged; since the sounds after stopping the engine will drain the capacitor.
How much space do I need? 
Where can I buy the capacitors?
Has anyone modified the Phoenix sound system to accomodate external charging?

Any and all help will be greatly appreciated.


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## Del Tapparo (Jan 4, 2008)

When I was in college, a 10 Farad capacitor was science fiction. They do now exist, but I think that is overkill in this application. I'm just guessing, because I haven't tried it, but I think something on the order of2000 to 5000 micro farads would be enough. I just saw an old PH Hobbies sound system the other day. It had a cap, no battery. That is probably the size cap it had. 

No. You don't charge your capacitor with a battery charger! The cap will charge back up when you apply power to it under normal conditions. There will be a delay in hearing sound until it is charged up. 


I am sure that someone with experience will chime in, but wouldn't it be better to direct this question to Sierra and Phoenix, since you are modifying their equipment?


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## Hans Larsson (Apr 19, 2009)

Interesting question. 
I need to dig out my school knowledge, only 20, hmm, 30 years ago... 

The Sierra battery has a capacity of 500 mAh at 6 V. That is an energy of 6 * 0.5 Wh = 6 * 0.5 * 3600 Ws = 10,800 Ws. 

The energy stored in a capacitor is: C*U*U/2. So for a capacitor to store 10,800 Ws of energy at 6 V, it would need a capacitance of: 
C = 10,800 * 2 / (U^2) = 10,800 * 2 / 36 = 600 F. 

How far would a 10 F capacitor reach? 
Well, first a 10 F capacitor is usually rated at 2.5 V. So you would need 3 capacitors in serial for a 6 V source, which results in an equivalent of a 3.3 F capacitor at 6 V. 

That capacitor can store C*U*U/2 Ws of energy, which is: 
3.3*6*6/2 = 60 Ws. 

In idle mode, the Sierra draws around 30 mA (according to George Schreyer's very nice www.girr.org pages). 
The power the Sierra draws is then: 6 * 30 = 180 mW = 0.18 W. 

The 3.3 F capacitor should then be able to supply power for: 60 / 0.18 s = 333 s = 5 1/2 minutes. 

Do you want the idle sound to be going for a longer time? Then you need more capacitors, or keep the battery.


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## Doug Bowman (Jan 8, 2008)

5 1/2 minutes is plenty of time. Just want to hear the shut down sounds and more importantly; when I start up, I want to hear the bell and whistle as I increase the voltage, not the chuff when the engine has moved 2 or 3 feet. It's been 40 years since my school days; your memory is a lot better than mine. Thanks


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## Greg Elmassian (Jan 3, 2008)

Realize that the capacitor will discharge when not being "charged"... unlike a battery. How much depends. But if you put it on the track after storage, it does have charge like a battery. 

So, shut down, and power interruptions ok, startup, nope. 

Greg


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## Dan Pierce (Jan 2, 2008)

I have used 4 10 farad caps in series with a 7808 voltage regulator for charging on the LGB sound units and the sounds last for approx. 30 seconds. 
Better cost than purchasing the vendors storage unit which is super caps. 

This works great on my analog layout and I used the LGB 6500x sound units. 

If I remember correctly, some sound manufacturers started using super caps instead of batteries as an option. 

No longer a need down the road to disassemble a unit for a battery change. 
Also, no long term storage issues with battery charging with these capacitors, works for me.


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## Doug Bowman (Jan 8, 2008)

Since both the Sierra and Phoenix Sound systems have charging circuits for the batteries; which are regulated. I am going to assume that those voltage regulators would work for charging the capacitors. So it sounds like I just need to build a capacitor bank that will fill my needs. Now to figure out how many I can fit in the space.


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## Michael Glavin (Jan 2, 2009)

Four capacitors in series skews the math and resulting Voltage and Capacity as compared to Hans calculations above for three 10F capacitors. Which maybe a good thing for LGB sound stuff, i.e., higher voltage out the gate. 

Dan do you have any additional info on the actual voltage cut-off and consumption of the LGB stuff in play? 30 seconds ON time seems diminutive compared to the calc for the Sierra card. Perhaps the voltage decays to quickly to realize the stored potential. What are you regulating with the 8V regulator, charging Voltage or Voltage to the card?

4) 10 F caps in series = 10V and 2.5F. 

FWIW: For those that don’t know! Stacking capacitors in series increases Voltage and reduces Capacity herein. Capacitors in Parallel increases Capacity and reduces Voltage. There is a simple formula that allows one to calculate realized values of sieries and parallel connections. 

Michael


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## Doug Bowman (Jan 8, 2008)

In looking at the charge specs for the sealed lead acid battery used in the Sierra system. I see that the "charge voltage" should be held between 7.2 and 7.35 volts until the current reaches a certain level. The "continuous charge voltage" is 6.75 to 6.90 volts. There in lies a problem in my opinion with the battery backup; In order to reach the continuous charge voltage level of 6.75 volts. I am running track power so with a Heisler Engine: at 6.75 volts it is hauling pretty good around the track and at 7.35 volts it is running too fast to look realistic. According to the specs on the Sierra card the "Start" voltage is 1.0 volts; Bell on voltage is 2 volts; Bell off voltage is 4 volts. It doesn't actually say what the voltage is when in the sensor switch mode for the "Chuff". I haven't actually measured it at the time the chuff sounds but it must be 5+ volts or better. So by the time you reach the 5 volt level the engine has moved some distance down the track before any sound is heard. So I'm asking myself; If the start voltage is 1 volt and the Bell on voltage is 2 volts. Even with a dead battery why don't I hear these sounds as I turn the throttle up. In most cases I will hear the directional whistle blow, but sometime after the engine is moving. With a charged battery everything seems to be normal. I have not tried to run the card without any battery at all to see what happens. I'm sure there would be no shut down sounds such as blowing off steam and the stop whistle. But what about the start up? I think I will see what happens. A very similar anomaly occurs with the Phoenix card in my Shay engine until the battery is charged up somewhat. The Phoenix battery is a Ni-Cad from what I can remember and as of this date it is 7 years old. The full charge rate for the Ni-Cad is 8 volts; again the engine is running too fast to be realistic. I'm not sure the capacitor system will resolve any of the speed problems, but at least I would not have to replace the capacitors like I do the batteries. But I would like to try it before tearing into the engines and installing diodes in series with the motors to slow the speed down to something that looks reasonable. My thought being with the diodes, 1 would give me a .7 volt drop and if room allows 2 would give me a 1.4 volt drop. This may be enough to prevent the engine from moving before the sound card comes on and give me a higher charging voltage without the speed increase.
Any and all input is welcomed. Thanks


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## Greg Elmassian (Jan 3, 2008)

Since the motor can run in both directions, you need 2 diodes to drop .7 volts, etc. One connected in each direction. More drop, more pairs of diodes. 

Regards, Greg


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## Michael Glavin (Jan 2, 2009)

Playing around on the bench my Sierra card consumes between 40-330mA shutting down depending on the noise(s) in play (about 30 seconds) then 30mA with a static noise level (about 2 minutes) and finally has a quiescent current draw of 20mA with all noise expired. Average current once track power is removed is probably about 60mA making various noises. 

The battery back-up drops in/out once 8.0V track power is realized and 6.0V battery power is present; at this time it starts charging the battery at 6.0V, at 9.5V track voltage the charge circuit tops out at 6.9V. 

When the battery circuit is flat (0V) and track power is increased from 0 to 2.5V the charge circuit begins to provide voltage, the board starts clipping at 6.0V with charge voltage at 3.8V. Once 8.0V is reached the board comes alive and provides 5.6V charge voltage and it needs to ramp up to 9.5V to deliver the rated 6.9V to charge the battery. 

There are some user adjustable variables in play which will more likely than not effect your numbers, the Sierra card I used is for a Mikado with factory default programming. 

I wanted to try this super cap idea once previously and got sidetracked and never went there. I have some 10F/2.7V super caps on order. I’m looking forward to taking a test drive. I suspect voltage decay will be an issue, the Sierra starts clipping when battery power decays to 4.5V. 

Michael


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## Michael Glavin (Jan 2, 2009)

Whoops, hit the send button twice....


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## Doug Bowman (Jan 8, 2008)

Michael; I believe you are right about the "clipping". I think that is the sound I hear when the battery is dead and the speakers sound like a machine gun. So my thought with using the capacitors is that after the engine has set idol for a day or two; I would expect that any charge that may have been held in the caps would be discipated. Prior to starting the engine and flipping the sound switch on, if I were to plug the charger that I used for the battery into the engine it would charge the caps for that initilal startup sounds. Once the engine has run for a period long enough to charge the caps and give me the shut down sounds, if it does not give me the bell and whistle on start up I would think it's just a matter of the capacity of the capacitors. Does that make sense to you?


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## Doug Bowman (Jan 8, 2008)

Greg; I understand about the diodes having to be paralleled; one in each direction. Thanks for pointing it out. Now to see if there is enough room for such a modification.


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## Greg Elmassian (Jan 3, 2008)

If you get some perf board and stack the diodes in, you can make it pretty compact:










About 3.5 volt drop... 0.1" spacing on on the circuit board











Greg


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## Doug Bowman (Jan 8, 2008)

Greg; I like that idea, Thanks! I'll post photos here when I get something built.


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## George Schreyer (Jan 16, 2009)

you might be better off just replacing the battery with a better one. SuperCaps are still pretty expensive, for $15 or less, you can get 5 NiMH AA or AAA cells to make a 6 volt pack that will fit right where the current battery is. I have some of these in service for nearly 10 years, all still going.


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## Trains West (Oct 4, 2008)

http://www.dallee.com/9V%20Replacement.html


dallee makes drop in 9 volt replacements ...... we put them in mth locos all the time


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## Hans Larsson (Apr 19, 2009)

If I remember right, the first regulator on the Sierra board delivers 7.5 V, from the inputs at 7 and 8 (through a bridge rectifier). 
This is then fed to the battery, through a diode. The battery charge voltage is then around 6.8 V. 
The battery voltage is then fed to the second regulator, which delivers 5 V to the electronics. 

At 6.8 V charge, I would use 4 capacitors at 10 F like Michael suggested, which gives 2.5 F. 

One problem with my original calculation is that the Sierra board cannot use all of the charge in the capacitors; when the voltage gets too low, it will start to motorboat. This seems to be at around 4.5 V. 

So the energy that the Sierra board can use is the difference of stored energy between "charge" voltage and "motorboat" voltage. 

At 6.8 V, the capacitors store 2.5 * 6.8 * 6.8 / 2 = 58 Ws. 
At 4.5 V, the capacitors store 2.5 * 4.5 * 4.5 / 2 = 25 Ws. 
The difference is: 58 - 25 = 33 Ws. 

If the Sierra board draws 30 mA at (an average of) 6 V, the sound will be going for: 33 / (6 * 0.030) = 180 s = 3 minutes. 
And if the Sierra draws 300 mA, the time will be just 18 seconds. 
The sound time you will get depends on the current consumption of the Sierra board.


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## Doug Bowman (Jan 8, 2008)

In reference to George's comments on using NiMH batteries. Can I use the existing charger in the Sierra system. I believe the Phoenix system uses the NiMH batteries or is it NiCAD? I have been under the impression that the NiMH and NiCAD batteries require a special chargers. Am I wrong?


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## George Schreyer (Jan 16, 2009)

They don't require special chargers at low charge rates. You can just hook them up. HOWEVER, since the capacity of a 5 cell NiMH pack is usually about double (or more) compared to the gelcell that it replaced, it will take a while to achieve full charge.


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## Dan Pierce (Jan 2, 2008)

For a diode drop, I use a bridge rectifier with the AC terminals a series connection to a load (motor), and I short the DC plus to minus. 
This gives a 2 diode drop in both directions. Do this a second time and it is 4 diodes in series. Much less soldering and wiring than using separate diodes. 


Of course the diode bridge could have .3 volt drop diodes inside instead of .7 volts, you have to check the specs to get what is needed. 

If matching motor speeds, .3 dropping diodes could come in handy for fine tuning.


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## Doug Bowman (Jan 8, 2008)

While at Wal Mart today I picked up 2 wireless phone battery packs rated a 600ma/hours each at 3.6 volts. Connected them in series; connected the bank to a variable DC power supply set at 7.26 output. Instructions say to charge for 16 hours prior to use. So I'll give it a try. The two packs cost $5 more than a replacement battery (lead acid) but if it lasts twice as long, it will be worth it. I'll post the results. It looks like they will fit where the old battery is today. Will find out tomorrow.


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## Doug Bowman (Jan 8, 2008)

Looks like the diode installation may be next, based on the info Michael posted earlier. 8 to 9.5 volts is way too high for the speeds I want to run. Now to figure out how to install them in my LGB Porter and Bachmann Shay. Then I'll take a look at the Climax and Heisler which have Phoenix systems. Any info would be greatly appreciated.


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## Del Tapparo (Jan 4, 2008)

Posted By Doug Bowman on 24 Nov 2010 12:44 PM 
While at Wal Mart today I picked up 2 wireless phone battery packs rated a 600ma/hours each at 3.6 volts. Connected them in series; connected the bank to a variable DC power supply set at 7.26 output. Instructions say to charge for 16 hours prior to use. So I'll give it a try. The two packs cost $5 more than a replacement battery (lead acid) but if it lasts twice as long, it will be worth it. I'll post the results. It looks like they will fit where the old battery is today. Will find out tomorrow.

Nothing wrong with the original batteries. It is the charging system that doesn't work. Every Sierra board/owner I have ever known has had the same old problem.


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## George Schreyer (Jan 16, 2009)

Actually, there is something wrong with the original batteries. That was the chemistry selected. Lead-acid batteries do not tolerate being run flat and left that way. This will happen every time the user forgets to flip a switch to disconnect the battery. After few of those cycles which cause the cells to sulphate, the batteries are toast.


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## Del Tapparo (Jan 4, 2008)

Posted By George Schreyer on 24 Nov 2010 02:22 PM 
Actually, there is something wrong with the original batteries. That was the chemistry selected. Lead-acid batteries do not tolerate being run flat and left that way. This will happen every time the user forgets to flip a switch to disconnect the battery. After few of those cycles which cause the cells to sulphate, the batteries are toast. 
Same battery is/was used by Phoenix ... no problems. Also no switch. It is the design of the board, not the battery.


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## George Schreyer (Jan 16, 2009)

I can use the same argument. Same sound system, different battery... all is good for MANY years in several systems. 

Perhaps the Phoenix board, which I do not have, draws much less standby current and doesn't flatten the batteries like the Sierra will.....


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## Del Tapparo (Jan 4, 2008)

Posted By George Schreyer on 24 Nov 2010 06:40 PM 
I can use the same argument. Same sound system, different battery... all is good for MANY years in several systems. 

Perhaps the Phoenix board, which I do not have, draws much less standby current and doesn't flatten the batteries like the Sierra will..... 
So which batteries do you use that work George? That would be useful info. 

But if you have to change battery chemistry to make a board work that was designed for and sold with gel cells, then I still say it is a hardware design problem.


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## Doug Bowman (Jan 8, 2008)

If I may chime in here. I have two engines with Phoenix systems and they both have either Ni-CAD or Ni-MH. It's hard to tell since they are enclosed in heat shrink. They are not the lead acid batteries used in the Sierra systems. I do understand the sulfate problem in lead acid batteries, it is really prominent in the smaller batteries like those used in motorcycles and lawn tractors. Rarely do they last more than a year unless they are put on some kind of maintenance charger. The auxillary charger that is used on the Sierra system is nothing more than a 6 volt DC power source as far as I can tell; so I believe you can damage the lead acid battery just as quickly by over charging. I had timers on those units that limited the time to 1 hour out of 24; that could have been too much if the engines sat idol for days or even weeks. I'm not sure the same thing won't happen on the Ni-MH batteries; overcharging I mean. I plan to install the new battery pack in the Shay tomorrow, so we'll see what happens.


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## Doug Bowman (Jan 8, 2008)

Dan; Where did you get your bridge rectifiers? In looking at the engine schematics it appears that it won't be a difficult task since they are both DCC ready. Just a matter of installing the bridge in series at the point where the motor leads terminate on the circuit board. I'm going to do some data collecting on the engines tomorrow, such as at what voltage does the engine start to move, sound come on and so forth. As I stated in the post above, the battery pack will go in tomorrow.


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## Greg Elmassian (Jan 3, 2008)

Radio shack has them off the shelf. 

Greg


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## George Schreyer (Jan 16, 2009)

I use no name NiMH cells, 5 in series. They take hours to charge fully but they get enough in regular running to work well enough.


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## Doug Bowman (Jan 8, 2008)

Installed the 2 banks of 3.6 volt Ni-MH batteries wired in series into the 2 truck Shay with Sierra sound card. Here are the results. 
Card on: 1.0 volts
Whistle: 2.0 volts (direction)
Bell: on at 4.0 volts; off at 6.0 volts
Engine moves at 3.75-4.00 volts
My limit for realistic speed 9.0 volts
Engine stopped: 5 seconds later whistle (stop) blows; at 15 seconds and 1 minute, coal shoveled; 1 minute 20 seconds, blow down; 3 minutes 10 seconds sound shuts off.

As stated earlier, I precharged the batteries prior to installation.
*I did notice that in the Sierra sound manual it says not to use Ni-CAD or Ni-MH batteries with their systems. So to do so is somewhat of a risk, I guess. * I figured since they are no longer available; if I fry something I'll just have to upgrade to a Phoenix system. 
When compared to the old 2k2 Phoenix system with a 7 year old Ni-?? battery installed in a 2 truck Climax.The battery was too low intitially to get any start up sounds. But after running the engine for 20 minutes the batteries had charged enough to get the following results.
Sound on: 2.0 volts
Whistle: 3.0 volts (direction)
Bell: on 3.0 volts; off 5.0 volts
Engine moves at 3.0 volts
Engine stopped: all sounds of at 30 seconds
My limit for realistic speed; 7.0 volts.

*Conclusions:* The higher voltage requirement to get a full charge on the batteries; 9 volts on the Sierra system; 7 volts on the Phoenix 2k2 system coupled with the extended shut down of the Sierra card (3 minute plus). May be why the the Ni-?? have outlasted the Gel Cells 3 to one. 
I am sure that with a capacitor system there would not have been sounds at start up. I'll let the engine set idle for 24 hours with the Ni-MH batteries to see how they work out. The true test will be after the engine has set idle for a month or so.
It will take some time to determine the fate of the new batteries and the Sierra system with Ni-MH batteries.


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## Dan Pierce (Jan 2, 2008)

On-line houses such as Digi-key, allelectronics, MPJA, Newark are just a few that have all sorts of parts. 

And much cheaper than the Shack. But when you are desparate for one part immediately, the Shack is an option. 

Note that I have just learded a better way for multiple diode drops. 

Use the bridge rectifier with the AC (~) leads in series with the motor(load) and instead of a short on the + and - terminals, just add diodes in series and they do not need to be back to back as the DC current only flows in one direction. The bands will always point to the - terminal.


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## Doug Bowman (Jan 8, 2008)

I don't know whether to be disappointed or not. Switched on the sound today and it was there. WAH LAH! But then I ran the engine around the track for about 10 minutes and the motorboating started. Checked the voltage on the track for the speed I like to run; only 7 volts; not enough to charge the batteries with the Sierra system. Before I go back to the gell cell batteries I'm going to install the bridge rectifier and a couple of diodes to give me a 2.1 volt drop to the motors. I think if I can keep 9 volts to the Sierra card and have 7 +- volts at the motor I'll have what I want. If not I will go back to the gell cells and keep the diode array in place.


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## Michael Glavin (Jan 2, 2009)

Doug, 

I’m assuming you have NiMh batteries; a battery rated @ 3.7V is the reason herein. 

If it were me I would fully charge the battery prior to anticipated use as a regular routine operation and on occasion or dependent on how long it lay dormant a charge/discharge/charge cycle would be desirable IMO. 

NiMh cells benefit greatly from a break-in charge regimen. In my experience with NiMH batteries they need to be "charge formed" (term was coined by a battery engineer-expert), this means you need to charge-discharge multiple times to wake them up and bring them to there full capacity potential. I can offer from many-many-many loaded discharge and charge regimens evaluating different battery technologies for Giant Scale R/C Aircraft that there is an obvious benefit to training these cells when new... I cycled several hundred NiMh battery packs with dedicated PC equipment monitoring what if scenarios, best case IMO is quick charge to peak at C/2.5 (must use a NiMH peak charger) and low and slow trickle charge to balance the cells for several more hours for normal use. That said NiMH suffers higher numbers from self discharge than other technologies. And NiMH is known to deliver rated voltage longer through a discharge curve than other chemistries. 

If you don't have an automatic charger/discharger simply charge at C/10 (capacity divided by 10 or 10% of the rated capacity per hour) for a maximum of 15 hours and discharge with a simple bank of #1157 automotive light bulbs until you hit .9V per cell LOADED or in your case 2.7V per battery. Three to four complete cycles typically garners rated battery pack capacity. FWIW: Not all NiMH batteries are created equal there are lots of CHEAP batteries out there, in this case there is NO perceived value you simply get what you pay for! 

C = battery capacity typically Ah (Amp hours) or mAh (milli-Amp Hours) 
mA = milli-Amp; Amps x 1000 
1 Amp = 1000 mA (milli-Amps) 
C/10 = battery capacity divided by 10 
C2 = battery capacity multiplied by two 

For some this “C” or capacity thing is peculiar; batteries are rated in Amp Hours or in our case mAh. A 2.7Ah or 2700mAh battery is supposed to deliver 2.7 Amps for one hour at rated voltage at C2 discharge (2700x2 = 5400mA) (5400mA/1000 = 5.4A). C/10 charge current would be 2700/10 = 270mA or 270/1000 = 0.27A 

Michael


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## Doug Bowman (Jan 8, 2008)

Michael: Thanks for all of the information. The batteries I chose are used in AT&T wireless phones. 3.6 volts at 600 milliamp hours. With the two in series it's 7.2 volts. I don't have a charger designed specifically for charging the Ni-MH batteries. What I did do prior to installing them in the engine was to connect the bank to a regulated variable voltage DC power supply set at 7.3 volts. I left it connected for about 18 hours. When I disconnected the power supply and read the battery bank (not under load); it read 7.26 volts. so I installed it in the engine. 
My engine has the ability to switch the motors off but still power the sound card. The only drawback is that with the card powered there are still sounds that are audible. My thought is, if the batteries charge when I'm running the engine at 9 volts+ I should be able to set the engine on a siding with power to the track and leave it that way for the 15 hours. The only thing I don't know is at what rate the card is charging the batteries. If this is a proper approach I could use the auxillary charging jack to recharge the batteries on a timer. I could also rig up something that would run them thru the charge and discharge cycle routinely when the engine is not in use.
Am I using an approach that wil work? I don't know where I would find a Ni-MH charger rated for 7.2 volt battery. The only thing I could think of is to use the old wireless phone base unit, but that will mean I would have to separate the 2 batteries in order to charge them. That would be a bit of a pain. Any thoughts on this?


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## Greg Elmassian (Jan 3, 2008)

Get a Maha 777 Plus charger or other intelligent charger. Charging by constant voltage (and I have done it for 25 years) is tricky and needs to be monitored for excessive current draw. You normally charge at about 1.4 volts a cell, but that's not how you "set it up"... charging by constant voltage only and getting a full charge requires a power supply controllable and regulated to 0.01 volts. 

If you charge at a voltage lower, and it is regulated, you can do it sort of, but you will not achieve a full charge. 

Regards, Greg


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## Doug Bowman (Jan 8, 2008)

Boy! So much info so little time. OK; more questions: In the Phoenix systems I am not sure whether they use Ni-MH or NiCAD batteries, actually I'm not sure it is either one. The Sierra system original was a small 500mAh lead acid (gell cell?). If the Sierra system does not have an "intelligent charger" to maintain the battery while the engine is powered. Would I be better of just to go back to the gell cell technology? It sounds like ther is an awfull lot to charging and maintaining these "N" type batteries. I would find it hard to believe that Phoenix or Sierra would have this technology built into their boards. although the newest Phoenix system boast a 3.6 volt Ni-MH battery. OH! What should I do?


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## Michael Glavin (Jan 2, 2009)

Doug, 

The problem has been and always will be the 6.9V charge voltage provided by the sound card. You really need at least 1.4V per cell (8.4V) to charge a six cell battery. Current is a factor too. NiCads have low internal resistance; accordingly adequate charging can be realized with multiple cells in series. 

Chargers are inexpensive to ridiculously priced and widely available! I've seen simple auto chargers for $9.95 however if you're aware and follow recommended practices you can charge with a power supply or wall wart power supply rated at 12V/60mA for about fourteen hours! 

Regulating the charge current is paramount as the actual voltage will vary and is temperature dependent. NiCd/NiMH batteries require constant current chargers maintaining the current setting over the entire charging period. An unregulated DC power supply with a series resistor limiting the charging current will suffice. You can take the KNOWN charge voltage and charging current and use Ohm's Law to calculate the value for a series resistor. 

Michael


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## Greg Elmassian (Jan 3, 2008)

In order for that method to be "safe" you have to calculate the circuit based on the assumption that the battery is 0 ohms. 

So, this kind of charging is not optimal in terms of time, and more importantly, not the best in terms of life of the battery, which is how we got here if I'm not mistaken. 

Regards, Greg


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## Michael Glavin (Jan 2, 2009)

Doug, 

In our circumstance with a 6V Gel, SLA or Lead-Acid battery (3-cells in series) continuous trickle charging requires a charging voltage of 2.3V per cell or 6.9V when the battery is coupled to the charger and not in use, the charge voltage is always held constant. 

These Gel or sealed lead acid batteries can either be trickle or cyclic charged, Cyclic chargers should charge at 2.4 or 2.5 volts per cell for specific time and be current limited to prevent overcharge. 

Michael


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## Doug Bowman (Jan 8, 2008)

Aren't the Gel cell (lead acid) batteries sort of self regulating when charging? Like an automotive battery; when first connected to a charger they draw substantial current and as the battery charges the internal resistance increases and the current drops back until it reaches some nominal value depending on the condition of the battery. I've been playing around with an old phone charger which is rated for a 3 cell battery pack. Watching the voltage change as the battery is charged. Unfortunately it is only rated for a 3.6 volt battery; in the charge mode it is putting out 4.2 volts right now. I had this crazy idea that if I wired two of the cell phone chargers in series just like the batteries. I wonder what would happen? Would it work?


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## Michael Glavin (Jan 2, 2009)

Greg, 

With a MAXIMUM charge time window and proper specifications / calculations I fail to see how the aforementioned simple approach is detrimental to battery life expectancy. 

Since we already know the required current we calculate for resistance. If we used “0 = R” as the value in a current calculation wouldn’t the sum be infinity I=E/R? 

Ohms Law calculate for resistance; R = E/I, 12V/.06A = 200 Ohms 
Ohms Law calculate for current; I = E/R, 12Vx200Ohms = .06A = .06x1000 = 60mA 

FWIW: Sanyo’s quoted internal resistance of a 600mAh NiCd cell is 9.5mΩ. 

Michael


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## Greg Elmassian (Jan 3, 2008)

I would be happy to explain in detail some time, but no reason to derail this thread, so I will summarize: 

Low constant current charging usually forms conductive crystal "dendrites" which are responsible for the so called "memory effect"... 

What you want is a higher initial current, throttled back to minimize heat, and tapering off to a "float charge" for nicads, and to a lesser degree nimih. 

Lack of "exercise" can cause internal defects. 

Regards, Greg


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## Michael Glavin (Jan 2, 2009)

Doug, 

As you suggest when a discharged Lead Acid battery is connected to the appropriate constant voltage charger (battery cell count dependent), a moderately high charging current flows at first, and gradually tapers down as the stored charge accumulates, once a full charge is reached the current drops to a low or constant level. 

You cannot stack the chargers in series…. A simple approach in your circumstance would be to bring out a positive wire for each 3.6V battery and charge them individually. 

Michael


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## Michael Glavin (Jan 2, 2009)

Posted By Greg Elmassian on 27 Nov 2010 12:20 PM 
I would be happy to explain in detail some time, but no reason to derail this thread, so I will summarize: 

Low constant current charging usually forms conductive crystal "dendrites" which are responsible for the so called "memory effect"... 

What you want is a higher initial current, throttled back to minimize heat, and tapering off to a "float charge" for nicads, and to a lesser degree nimih. 

Lack of "exercise" can cause internal defects. 

Regards, Greg 

Greg,

No one suggested constant charging at low current levels, a MAXIMUM time interval was qualified. Anywho even at C/10 these cells are good for routine charging and or normal use without detrimental damage to the cells. At C/10 these cells can absorb some overcharge, if heat builds a oxygen recycling catalyst mitigates damage to the cells, charge rates above C/10 overwhelm the aforementioned oxygen recycling; heat builds quickly and exposes the cells to chemical breakdown and shorter life expectancy. 

The so called “Memory Effect“ is a bit of a wives tale IMO and the term is often miss-used, some truths can be associated with the coined term, but in today’s world and applications it’s a virtually non existent. Dendrites are another story, and yes I understand how and when they come to play. Chemical breakdown of the cells and results thereof simply decreases the capacity, and is irreversible for the most part. 

I agreee with your comments _"What you want is a higher initial current, throttled back to minimize heat, and tapering off to a "float charge" for nicads, and to a lesser degree nimih."_ See my previous posts, I suggest same...

Michael


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## Doug Bowman (Jan 8, 2008)

Another question. Are NiMH and NiCAD batteries charged using the same process? We have a couple of different wireless phones in the house and one has Ni-CAD the other has Ni-MH both are 3.6 volt battery packs.


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## Michael Glavin (Jan 2, 2009)

Posted By Doug Bowman on 27 Nov 2010 01:48 PM 

Another question. Are NiMH and NiCAD batteries charged using the same process? We have a couple of different wireless phones in the house and one has Ni-CAD the other has Ni-MH both are 3.6 volt battery packs.


Doug, 

No, the algorithm is nearly identical and with auto-chargers a charger designed for NiMH cells is a must. NiMH chargers are often capable of charging NiCd, but a NiCd charger generally is not capable of sensing the diminutive bump or drop in voltage used to detect the end of charge. Typically a NiMH charger uses a different and or more sophisticated charge termination method. 

Michael


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## Greg Elmassian (Jan 3, 2008)

To amplify on Michaels comment (and I know you know what you are talking about Michael, was more concerned with newcomers that would leave on charge forever): 

Good chargers will look for termination in a DV/DT rate... the Delta Voltage over Delta Time... basically the rate of change of voltage over time... nicads will change voltage as they charge, and then peak and go down a bit... that "hump" or "dip" will signal the charger. 

Nickel Metal Hydrides, don't "dip" but go "flat"... 

A good charger will sense this... as well as have a temperature sensor, and smarts that pay attention to the whole process to see if anything goes wacky.... 

So, you should look for a charger that says it works for the chemistry you have, and also look for reviews on how the charger really performs. There's lots of claims of suitability out there. 

Regards, Greg


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