# Low Battery warning device



## sailbode (Jan 2, 2008)

In one of our recent battery discussions I mentioned that I had discovered a device sold to warn truckers if they were draining their batteries too much while not running the engine. I suggested to this forum this might work for us. Our resident experts said probably not as it was meant to work in a 12 volt DC environment. I contacted the maker of this device and asked if he thought it might work in a 14 volt or 18 volt system. He said he didn't know but offered to send me one to try out. He did. I did, and the results are in. This little *$30* gizmo works very nicely. When you turn on the power it beeps and flashes 3 times. Then the display indicates voltage. Now in my case, running one of Ricks Li-ion 18 volt packs, a fully charged pack shows close to 19 volts. A fully discharged packs shows approx 11.5 volts. Anything in between means mid charge and as I get used to the system, I will be able to anticipate the remaining battery life based on voltage. As the discharge rates are non-linear and will vary with different chemical batteries as well as the different loads of each different train, I expect that's the best we can hope for.....but it's something and I think useful. Now the low voltage alarm is very easy to set and I anxiously waited as my train ran and ran until the battery got to the low voltage setting....in my case 13.5 volt. Sure enough, the bright red LED started flashing and a loud pulsing beep sounded. Almost as loud as a smoke detector but not quite. My train ran for another 20 minutes with alarm sounding until the battery cut off voltage kicked in ( approx 11.7 volts). This is just what I've been looking for and the price is reasonable. I'm sure it's not for everybody, but for some, it might be a handy gadget. For anyone interested, the "Volt-Minder" can be seen and obtained from: http://www.voltminder.com/
Don


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## Del Tapparo (Jan 4, 2008)

It looks like this unit will work well for those having room in a trailing car and using a battery pack within the units adjustable warning range of 10.5V to 13.5V. This would include 14.8V Lithium-Ion, 12V and 14.4V NiCad/NiMh battery packs. I'm a little confused on your measurements though. The 18.5V Lithium-Ion battery pack on Rick's site indicates a cut-off voltage of 15V, not the 11.5 to 11.7V you are observing. That's quite a difference.

I haven't been able to find any operating voltage range of the VoltMinder. I did find that the display goes to 20V, and apparently you have demonstrated it will operate there without damage. I also found it for sale at BatterySpace.com for about $23.


Nice find Don.


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## Torby (Jan 2, 2008)

I made myself a low voltage cutoff, but it wasn't very successful. I already had dead cells in all 3 packs. As soon as the loco starts, the dead cells go to 0 and the cutoff cuts off. Fortunately, I'd put in an override switch. Train still runs around 2 hours on each of the 3 packs, even with dead cells. I figure if I'd put the cut off in earlier, I wouldn't have dead cells.


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## izzy0855 (Sep 30, 2008)

Hey Torby, 

Could you do me a favor, if you have a volt meter check the voltage of the 18.5V when your low voltage tester reads 15V and let's see if there the same. Because, draining any lithium battery-pack past the PCB cut-off voltage will damage one or more of the cells and you will not be able to recover that cell to it's full potential. Also, can you tell me what the voltage of the battery-pack is after it's third cycle. It should be between 20.7 - 21volts. Then after you check the voltage of the battery with a volt meter after it's fully charged, then attach Volt-Minder to the battery and see what it reads. 

Thanks, 
Rick Isard 
Cordless Renovations


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## Greg Elmassian (Jan 3, 2008)

I have not seen that it is certain that drawing a li-ion cell below the electronic cutoff voltage ALWAYS damages the cell. 

You can draw them down lower if you want... if you know what the danger is... 

(by the way, does anyone know what it is?) 

I'm not talking about the lessening of the number of total cycles here due to deep discharge. 

Regards, Greg


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## sailbode (Jan 2, 2008)

Rick, 
What is supposed to be the PCB cut off voltage on the 18v Li-ion pack you sold me?? I thought it was approx 12v???


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## Torby (Jan 2, 2008)

Sorry, Rick, all 3 of mine are 19.2v NIMH packs made of Tenergy cells. I can find the dead cells pretty easily with my dvm. Also, when I've been running them, the dead cells get warm before the live ones do. Fully charged, with all live cells, the pack is between 23 and 24v. The tenergy charger uses a thermocouple and watches for temperature rise to detect full charge.

If I can get the last 2 pay cuts restored I'd come see you about new batteries, but my employer's customers are loosing customers, so right now, I'm scratching for pennies.


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## Pete Thornton (Jan 2, 2008)

it might be a handy gadget 
Just as a portable voltmeter it looks pretty handy.


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## toddalin (Jan 4, 2008)

Easy stuff to do.

Just use a relay between the batteries and circuit board that is held energized when it has sufficient battery voltage. Use resistors or a voltage regulator to set the minimum voltage that holds the relay closed. When the voltage gets below this point, the relay opens and the other pole of the armature engages an LED telling you, "time's up." Try to find a low current relay as it will be a continual draw when operational.


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## izzy0855 (Sep 30, 2008)

Hello everyone, 

I talked with Gary Latinis from Volt-Minder today and he said the maximun voltage he had ever tested his device was 13.5V and he wasn't sure how high it could go? When he designed the Volt-Minder it was intended for Truckers and RVer's but he never thought it would be used for model train enthusiasts. 

Don, the IC chip will cut-off at 15V on our 18.5V & 12V on our 14.8V lithium-ion battery-packs. When the cut-offs happens, if you take a volt meter to the battery it will read either 3 volts or 3.1 volts...take this number x 5 = 15 volts. If for some reason the IC chip reads below 3 volts, give me a call and we'll replace the PCB Circuit Board. 

Hey Torby, that's fine, and in these times we all need to watch our pennies. When your charging the Nimh battery-packs, if the cells are getting warmer then luke-warm water when charging, you may have the amp's selected at a hgh rate. Discharge the battery as normal and when you need to recharge it again, select 500 milliamps charge current. A lower amp hour charge rate will keep the tempeature down and save your battery for the long run. Nimh batteries do not like to charged at a high amp hour rate or higher then 1.5amps. Charging a Nimh battery-pack higher than 1.5amps will decrease the number of cycles. 

Rick Isard 
Cordless Renovations


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## Torby (Jan 2, 2008)

I used an op-amp, regulator for voltage reference and 2 fet's. The circuit turns itself off when the battery voltage drops below the set point. Oh, yes, a trim pot to set the set point.

I have 2 1.5 amp chargers and 3 packs. One pack has too many dead cells for the charger to figure out the voltage, so it charges at like 50mA. After being on charge all night, the dead pack still runs the train about 2 hours.


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## Dave Ottney (Jan 2, 2008)

If you don't want to mess around with building your own LVC try one of these- 
http://www.dimensionengineering.com/LipoShield.htm 

Also look at their Cellshield. Both devices are made to protect lithium chemistry packs. I use the LipoShield in a couple of my planes that have older ESC's which are not "lipo aware". This is a good company with excellent service. 
Oh yea, both devices are really small. 
Dave


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## eheading (Jan 5, 2008)

Dave, that actually looks very interesting. I just might try one out and see how it does with my engines! Thanks for the lead!

Ed


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## TonyWalsham (Jan 2, 2008)

Dave, what does *..."2s to 6s"...* mean please?


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## sailbode (Jan 2, 2008)

Tony, 
I believe that is referring to the number of cells in a Lithium battery pack. 
D


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## TonyWalsham (Jan 2, 2008)

Hi Don. 

I don't think so because in some parts of the information on those pages they refer to cells spelt with a "c". 
Plus, they also say: 
*"Input voltage: 1s to 12s Lithium or Lithium Polymer "*. 12 cells would be over 44 volts.


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## Del Tapparo (Jan 4, 2008)

Tony - The "S" refers to series, and "P" refers to parallel. A 3S pack is three 3.7V cells connected in series to increase the voltage. A 2P pack would be two 3.7V cells connected in parallel to increase the current capacity. This terminology is used in describing the construction of Li-Ion and Li-Po battery packs.

For example, a Tenergy 14.8V, 4400mah Li-Ion battery pack is constructed of 8 18650 cells, each rated at 3.7V, 2200mah. Two sets of 4 cells in series are then connected in parallel. I believe this would be referred to as a 4S2P battery pack. (Someone please correct me if I'm wrong). Tenergy Battery Specs


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## TonyWalsham (Jan 2, 2008)

Thanks Del. 

I did not see any reference to "P" there.


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## sailbode (Jan 2, 2008)

I did a few more runs with the "Volt-minder" and I'm getting inconsistant results. Not sure if it's the "voltminder" or the cut-off circuit in the battery pack. will post answers if/when I get this sorted out.
D


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## Del Tapparo (Jan 4, 2008)

Posted By TonyWalsham on 04 Mar 2010 06:48 PM 
Thanks Del. 

I did not see any reference to "P" there. 

Here is a better example. 4S2P


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## izzy0855 (Sep 30, 2008)

Don, when I talked with Gary from Volt-minder, he said it was never tested over 13.5 Volts. So maybe it's just like our digital readers, we have to program the voltage range & mah's of the battery before it can read, and if you give it more voltage than it's programmed for, it will indicate different voltages every time to attach it? 

Rick Isard 
Cordless Renovations


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## sheepdog (Jan 2, 2008)

One other option. Since you need to read the voltage under full load and you most likely can't read a display as your train as it passes by, how about this?

Wireless Voltmeter 

Write a simple little app and make all the set points you want. Draw a graph and you can see when one of the batteries bites the dust (voltage drops like a rock).

*Craig*


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## sailbode (Jan 2, 2008)

Actually Craig, the voltminder is quite visible and readable as it passes....assuming you run the train at a reasonable speed.

Rick, the problem seems to be more in the packs pcb board cut off voltage. I don't know why but now the pack has been shutting off at around 14 volts which is actually closer to the 15 volts it is supposed to shut off at. I checked the digital display against my Fluke meter and they are within .5 volts. I'm measuring at the harness plug you provided (close to the battery) but under a 1.5 amp load. I'm disappointed the volt minder will apparently not work with the 18.5 packs but I suspect would work nicely with a 14 volt pack???. I will continue to play with this as I know at least one guy who could really benefit from such a devise.
Incidentally, this can not be replaced with an add on cut off voltage devise......need the display (fuel gage) and need the alarm to warn of impending shut down.
D


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## Dave Ottney (Jan 2, 2008)

Whoops, sorry for not checking back sooner. Del's explanation of the S rating is correct. When using lithium technology (LiIon or LiPo) the number of cells in series in a pack is referred to with an S after the number. The number of series sets of cells connected in parallel is the P number. Putting cells in parallel increases the capacity (milliamp hours). 
The devices I referred to from Dimension Engineering cut off the power to the throttle channel when the low voltage threshold (usually 3V/ cell)is reached thus preventing the over discharge of the lithium pack. The ratings for the LipoShield will definitely cover the voltage needs of model railroading- 1 cell to 12 cells in series- over 40V. 
Again Dimension Engineering is a very good company. 
Hope this helps. 
Dave


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## TonyWalsham (Jan 2, 2008)

Dave I most certainly bow to your depth of experience with flying packages, but I doubt seriously that shield can handle 40 volts. 
That be killing voltage with enough amps behind it. 

Now if the 12s was a misprint and they actually meant 12 in parallel I could believe that.


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## izzy0855 (Sep 30, 2008)

Don, not sure either but let's make sure you have fully charged the 18.5V battery-pack, then "put-it-in-play" and when it's shut-offs measure the voltage and let's see what your volt meter reads. Without a full charge the PCB circuit may not see it's limit and could be discharging below nominal voltage if it doesn't have a full charge. Check it out, and if it see discharging below 15 volts, give me a ring and we'll send you out a new battery-pack. 

Rick Isard 
Cordless Renovations


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## sailbode (Jan 2, 2008)

Just an update for those interested, I've been playing around with the "Volt-minder" using different batteries. I guess the issue becomes how much voltage do you need to power your particular train. I'm currently running a Bachmann 10 wheeler with an LGB sound tender and 7 illuminated passenger cars all controlled by one of Dels "Rail Boss" RC set ups. Using a "Cordless Renovations" 18volt Li-ion pack the train is capable of running crazy fast....and as I've mentioned, the "Volt-minder" is not compatible with a battery that has a safety cut off of 15 volts. Next I tried a 3200 mah 3 cell li-po (called 11.1 volts but in actuality fully charged measured 12.8 volts). With this pack the 10 wheeler required using full throttle to give a speed that was acceptable. With the pack discharging at this (full throttle) rate I got a run time of one hour but the volt-minder worked like a charm warning me when the predetermined 12 volts had been reached. Of course the pack could have gone lower but at those low voltages the trains marginal perfromence was fading. Next I tried a 3300mah 4 cell li-po pack (14.8...actual 16volts fully charged). This pack seems to be the winning combination for using the volt-minder with my Bachmann 10 wheeler. 3/4 throttle yields a nice brisk pace but not too fast (I'm checking the duration as I write this but I expect a much longer run).. Volt-minder alarm can be set for 12 -13.5 so I set it at 12.5 which gives approx 15 minutes before safety cut-off. I still like the volt minders easy to read illuminated display making a quick glance at the train as it passes easy to see how much is left in the battery. The alarm is quite laud and can easily be heard over the train sound and a bunch of friends chatting. Bottom line, if a train will perform well on a 14 -16 volt pack, the volt-minder is a neat option. I realize there are some train motors that really need at least 18 volts like my friends LGB A-B-A Sante fe. Just another black box gadget to amuse us if your operating system doesn't have it already.
Don


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## eheading (Jan 5, 2008)

Dave, I purchased one of the liposhields that you referenced in your post. When I got it, though, it looks like it needs to have a separate speed control from the receiver. Using my RC system (Aristo's Revolution TE) my receiver and ESC are integrated, and so their engineer and I decided it really wouldn't work in that application. It also indicates that it only works for single direction cases, which obviously doesn't apply to a train control.

Am I missing something, or is it truly aimed at aircraft operations, and not really applicable to our train applications?

Ed


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## Dave Ottney (Jan 2, 2008)

Hmm Ed, 
Interesting, I hadn't thought about the TE. I was thinking only about the 2 stick transmitter systems. The reverse problem is a new one to me also. I'll have to rethink my recommendation but I think you have seen that the company is very supportive. 
Dave


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## eheading (Jan 5, 2008)

Dave, the company was not only responsive and supportive, but they even offered to take the device back since it didn't work for me. More than fair.

Ed


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## John J (Dec 29, 2007)

My Brain is fuzzy but I remember way back in time Doesnt a Zenen diode conduct once the voltage accross it drops below a certian point? There for a Zener diode inseries with a LED and appropriate resister cause the LED to light if the battery supply drops below a given point? I know there might be something worng with this idea


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## Greg Elmassian (Jan 3, 2008)

Nothing wrong, although a zener diode conducts above the set voltage. You can indeed put it in a circuit to have a led light at a certain voltage. 

Regards, Greg


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## John J (Dec 29, 2007)

Posted By Greg Elmassian on 23 Mar 2010 11:10 PM 
Nothing wrong, although a zener diode conducts above the set voltage. You can indeed put it in a circuit to have a led light at a certain voltage. 

Regards, Greg 

Back in the 70s, before I became a board changer, We use to have to come up with circuits of all kinds. I have not done this type of stuff in a long time. I use to make circuites just about every day.

Those wer the times when work was fun....A lot of fun.....When you sent your ideas back to the factory in Cleavland OH They were glad to get them and acknowledged your contributions.


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## sailbode (Jan 2, 2008)

It occured to me today that I could use an 18 volt pack and the voltminder if I opened up the pack and wired the warning devise to only 4 of the cells in the pack. Of course the display would be inaccurate regarding total voltage of the pack but If all I wanted was an alarm, that would probably work. Any thoughts? 
D


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## Road Foreman (Jan 2, 2008)

Tony, 

With Lion or Lipo batterys the "s" stands for series connection, the "p" stands for parelllel & the "c" is for the current.. 
You will see the batterys listed 4400 mA 4s4p & 10 to 12c.. This would be a 14.4 volt 4.4 amp battery that could put out 44 to 52.8 Amps for a short time.. This battery should be charged @ 1c or 4.4 Amps.. 

Hope this helps 

BulletBob


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## Torby (Jan 2, 2008)

JJ,I've been getting back into it. It's even more fun now as a whole computer costs $2. You just give it 2.5 to 5.5 volts and your program runs. The new surface mount parts are easy to work with. I just got a new programmer for $35. The old programmer still works, but it plugs into a serial port on your computer, and my netbook doesn't have a serial port.


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