# Lithium battery under voltage protection



## steam5 (Jun 22, 2008)

I just popped into my local hobby shop, They don’t do trains, but heavily into radio control cars and planes. I’m new to battery power and currently use NiCd batteries. I took the time to talk to the guy about lithium chemistry batteries.


He told me you need to make sure you don’t let lithium batteries drop below a certain voltage. I’m sure he stated a voltage, but it slips my mind. I remember a thread on MLS that this cut off voltage was mentioned and discussed, but I don’t remember a solution to the ‘problem.’
He did show me this interesting product which connects into a ESC:











http://www.dimensionengineering....ld.htm


This product I guess could be used on systems such as RCS – Beltrol? I don’t think it could be adapted to systems like Airwire…


How do you make sure you don’t drop below that certain voltage to ensure no damage to your batteries?


Alan


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## Dick413 (Jan 7, 2008)

my batteries came with a built in cut off, they are 14.8 with a cut off of somewhere around 9 volts. 
the batteries that we use gen. come with a cutoff so you can not over chg. or over dischg. rc batteries do not.


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## steam5 (Jun 22, 2008)

Is it normal to have the cut off circuit built into the batteries, or do you need to by a Rolls Royce of the battery world?


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## Dick413 (Jan 7, 2008)

yes to your first ? when you by a lypo it tells what it chgs. to and the low cutoff.


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## Del Tapparo (Jan 4, 2008)

The next generation of RailBoss systems, the *RailBoss Plus*, will address this problem. It will have a soft and hard cutoff for lithium batteries. The "soft" cutoff will warn the operator when he has about 10 minutes of battery power left by cutting power to the loco and flashing the front light. This gets your attention right away and wondering why your train slowed down or stopped the flashing light will tell you it is a low battery. Moving the throttle back to minimum will reset it so you can get the loco back to a desirable location under full power. The whole idea is to warn you prior to the safety PCB in the battery pack stopping the loco dead in its tracks. There is also a hard cutoff, which will stop the loco dead when battery voltage gets way too low. This will primarily be useful for Li-Pos that have no other means of protection.

This system is built in to the RailBoss. No add-on boards. It will be available this Spring. There will be other new features as well, but they don't pertain to the topic of this thread.


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## East Broad Top (Dec 29, 2007)

The packs I get (Tenergy 14.8 v from all-battery.com) have built-in under/over-voltage protection. It's a PC board that fits on the end of the battery pack. It's also something of a de facto fuse in case of a short. It'll pop pretty quick, protecting the cells. Of course, then you get to have the fun of replacing the PC board. 

Later, 

K


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## Stan Cedarleaf (Jan 2, 2008)

Steam.... Like Kevin and Dick, I use the Tenergy 14.8 4400 mAh Li-ions as Cordless Technology's 14.8 5200 and 18.5 5200 Li-ions. They all have built in protection for both over charging and cutoff for under voltage. It's very important that the proper type of charger be used for each battery voltage. 

I think it's very inovative that Del will be adding this protective circuit into his new Rail Boss. Digital cameras have had that type of protection in them for many years.


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## steam5 (Jun 22, 2008)

Maybe the batteries they had in the shop didn't have the protection circuit built in... The protection Del described is what the guy in the shop said about the little protection circuit does above in my first post. 

So if I go Li-Ion 
-make sure I get a pack with built in under/over voltage protection 
-Get the proper type of charger 

Alan


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## Dick413 (Jan 7, 2008)

yes alan that is right, but i like what you and del talk about the one in my battery's, it just cuts off 
i have derailed some trains when this happens.


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## steam5 (Jun 22, 2008)

Dick, do you notice when the battery is about to cut out? Or does it just stop?


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## Del Tapparo (Jan 4, 2008)

Posted By steam5 on 01 Feb 2011 04:40 PM 
Dick, do you notice when the battery is about to cut out? Or does it just stop? 
Due to the protection PCB in Lithium-Ion battery packs, power is removed instantly, without any warning or slowing of the train. The low battery warning circuit in the RailBoss Plus will warn you when you have only a few minutes of time left before that happens, letting you get your train back home under power, instead of fishing it out of a tunnel. The RailBoss warning levels are adjustable, so after a few trial runs, you will know exactly how much time you have left when you get the warning.


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## steam5 (Jun 22, 2008)

Del, 

that exactly how the guy in the shop described it. I can understand why that behaviour is needed when flying model planes! 

Alan


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## Mike Reilley (Jan 2, 2008)

If you use 7.4v, 11.1v, or 14.8v LIPO cells THAT HAVE A BALANCING PORT....then you can use one of these to signal when the battery is getting low. 
http://cgi.ebay.com/RC-Lipo-Battery...564224b5fc


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## Del Tapparo (Jan 4, 2008)

Posted By Mike Reilley on 01 Feb 2011 05:58 PM 
If you use 7.4v, 11.1v, or 14.8v LIPO cells THAT HAVE A BALANCING PORT....then you can use one of these to signal when the battery is getting low. 
http://cgi.ebay.com/RC-Lipo-Battery...564224b5fc



I hope it is a loud buzzer! The LEDs certainly won't do you any good running a train.


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## Mike Reilley (Jan 2, 2008)

95 db is the sound level at which hearing loss BEGINS....it's REAL loud.


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## Dick413 (Jan 7, 2008)

alan,del said it that's what can happen. but i know now my run times so it does't happen that much any more.


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## TonyWalsham (Jan 2, 2008)

Del has a neat idea. 

However, it would still be vitally important to have the circuit protection built into the battery. As much for the charge rate as the low voltage.


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## Dick413 (Jan 7, 2008)

tony that is just what i was thinking, something that would be wired into the engine so that i 
could change my bat. out for charging.


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## Del Tapparo (Jan 4, 2008)

Posted By Mike Reilley on 01 Feb 2011 06:05 PM 
95 db is the sound level at which hearing loss BEGINS....it's REAL loud. 
Well, they say when your pack drops below a "Certain Level", damage can occur. At what level do they warn you? (they don't say). This is the point where you want to stop immediately! No time to get the train back home! This may be OK for Li-Pos, but will be of no value to those of us using Lithium-Ion with PCB protection boards built-in (which most do have).


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## TonyWalsham (Jan 2, 2008)

Not really Dick. 
It is important that the main circuit protection is built into the battery pack. Not the loco. 

What Del's idea will do is warn you the battery is getting flat and will allow you to get back to base rather than be stranded on the layout, in a tunnel for example. It will not be a substitute for the battery pcb. 

There are simple low voltage analysers available right now that can, for example, trigger the horn of a sound system to give you a continuous warning.


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## steam5 (Jun 22, 2008)

Posted By TonyWalsham on 01 Feb 2011 06:54 PM 

There are simple low voltage analysers available right now that can, for example, trigger the horn of a sound system to give you a continuous warning.


Who makes this?

Alan


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## Dick413 (Jan 7, 2008)

tony sorry that is what i meant, i take all my bat. out and put them in a can for chg. they all have a pcb


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## TonyWalsham (Jan 2, 2008)

*Low Voltage warning kit.*










I have built some and they worked well. You must use a filtered DC supply to set the voltage level accurately.
I substituted the LED for a sound trigger connection.


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## steam5 (Jun 22, 2008)

Tony, 

Thanks for the link. This could be a good little circuit. 

Alan


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## Mike Reilley (Jan 2, 2008)

Posted By Del Tapparo on 01 Feb 2011 06:30 PM 
Posted By Mike Reilley on 01 Feb 2011 06:05 PM 
95 db is the sound level at which hearing loss BEGINS....it's REAL loud. 
Well, they say when your pack drops below a "Certain Level", damage can occur. At what level do they warn you? (they don't say). This is the point where you want to stop immediately! No time to get the train back home! This may be OK for Li-Pos, but will be of no value to those of us using Lithium-Ion with PCB protection boards built-in (which most do have). 
Agreed...this gizmo is for LiPo batteries as far as I know. The "Certain Level" is 3.3v (look at the print on the back of the device in the top right photo). I'm NOT pushing this particular device, but if you run LiPos...and they have a balancing port, these kind of board seem to have made the grade in the RC flying world...and it's cheap. There are lots of makes of them. I just showed one that was easy for me to find on eBay. When they alarm at 3.3v, the fliers have enough time to get their plane on the ground without damaging the battery (i.e. discharging below 3.0v)...and yes, you can hear the "buzzer" when the plane is hundreds of feet away.

You hit on a critical point though. When looking at these kind of devices, you want to know the cutoff voltage they trigger at. And remember...these are for LiPo batteries ONLY (as far as I know) and ONLY LiPos that have the second wiring harness for charging/balancing...the balancing port. Batteries with JUST the power output wires will not work with this kind of device.


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## TonyWalsham (Jan 2, 2008)

Alan. Be careful. 
JayCar also had another (so called) low voltage measuring device. I could not get it to work at all. Then I found they had this one.


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## Dennis Paulson (Jan 2, 2008)

Posted By Del Tapparo on 31 Jan 2011 10:20 PM 
The next generation of RailBoss systems, the *RailBoss Plus*, will address this problem. It will have a soft and hard cutoff for lithium batteries. The "soft" cutoff will warn the operator when he has about 10 minutes of battery power left by cutting power to the loco and flashing the front light. This gets your attention right away and wondering why your train slowed down or stopped the flashing light will tell you it is a low battery. Moving the throttle back to minimum will reset it so you can get the loco back to a desirable location under full power. The whole idea is to warn you prior to the safety PCB in the battery pack stopping the loco dead in its tracks. There is also a hard cutoff, which will stop the loco dead when battery voltage gets way too low. This will primarily be useful for Li-Pos that have no other means of protection.

This system is built in to the RailBoss. No add-on boards. It will be available this Spring. There will be other new features as well, but they don't pertain to the topic of this thread.



Thats great news to me , I love my Railboss that I use already , and need the new Railboss plus with the low voltage LiPo battery cut off , so I can feel safer useing all my LiPo batterys , and not have to be so time minded with their use . Put my name on one of the new Railboss Plus products , please .









people who have seen me install the small LiPo battery in the baggage door and watched how long it runs are amazed , and they are impressed with the operation of the 2.4 transmitter , and the slow starts and stops it can perform . I am happy with the Railboss , and will be happier with the newer one .


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## Dave Ottney (Jan 2, 2008)

Del great news. This sort of protection circuit is what we have in modern ESCs for flying. I was wondering when the RR ESCs would have the circuits. It will be interesting to see how you do your circuit. On the flying ESCs the circuit detects the pack voltage when plugged in and then "adjusts" itself to the proper cutoff. Meaning it will sense the 11.x V of a 3 cell Lithium pack or the 14.xV of a 4 cell pack, etc and adjust the cutoff to 3Vx#cells for the cutoff voltage. 

BTW the Dimension Engineering product that started this thread works great. I have a couple of them for my older, non lithium aware ESCs so that I don't have to worry about over discharging my LiPo packs. 

As far as charging protection goes, I can only recommend charging outside the loco with a lithium capable charger. I think trying to put a charge protection circuit into an ESC would probably be rather difficult and drive up the price. Not only that but I treat all my lithium based packs (LiPo & LiIOn) with a lot of respect and charge them safely in a container or when at the flying field outside of the car on the pavement or grass. This is great technology if it is handled correctly. 
Dave 
Again I highly recommend RCGROUPS.COM , batteries & chargers forum for more info.


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