Device for LVC on battery discharger?

[DonA]

I have been researching the threads here in DIY Electronics looking for a device or circuit I can use to stop a discharge function for my lipos for storage purposes. Some are close, but not exactly what I need. Sometimes I go flying and don't discharge my last battery and it is going to be a while until I fly again. My TP1010C has a discharge function, but is very slow using only .5A as the max discharge rate. When you are flying 10S 5000mah lipos, the discharge takes A WHILE!!!

Here is what I want. A device/circuit that will control a relay that carries the discharge load, and open that relay when the battery has reached a certain voltage (3.85V for storage). I don't need the device to handle the discharge load, it only needs to control whether the load is active or not. My thinking is I only need to monitor one of the cells being discharged since all the cells will be approximately the same voltage, so the number of cells in the pack is irrelevant. I can externally manage the particular load being placed on the pack so if I discharge a 3 cell 2100mah pack or a 10 cell 5000mah pack, it doesn't matter.

Once the device is triggered, it closes a relay if the cell voltage is above a certain level and keeps it closed until the cell voltage drops below that level. It doesn't have to be super precise in measuring the cell voltage, and doesn't need to be adjustable voltage, tho that would be ok. I don't care if it has to be powered from a seperate source or is powered via the pack being discharged.

There are DIY devices/circuits here in this group that are close to what I want but for one reason or another don't satisfy my needs. I have used mechanical timers for this but a timer only gets me close to what I need and I always have to check if the voltage after discharge is what I wanted.

Anyone have any ideas, I would appreciate your input.

thanks
Don

[jackerbes]

The one in this thread, designed by Dan Baldwin, works well and is adjustable for different sizes of packs:

http://www.rcgroups.com/forums/showthread.php?t=725572

If you use that you should disconnect it after it cuts off as it does leave a small load on the battery. An hour or two probably wouldn't matter.

Jack

[DonA]

Thanks Jack

I looked at that thread previously but the upper voltages I need for 5S and 10S pack exceed what this circuit will manage. Maybe I will post in that thread to see what could be adjusted to handle these voltages.

Don

[rc404]

Actually I was looking at the referenced thread earlier today for exactly the same reason (discharge of 10s packs for a pattern plane) and also thinking it won't handle the full 10s voltage. But you make a great point. If you discharge the whole 10s through a load, you don't have to monitor the whole pack. Wouldn't the modified circuit work for this purpose?

[jackerbes]

In the early part of that thread the designer, Dan Baldwin, explains how to change the value of two of the resistors to change the range of voltages it will control.

Dan is a regular visitor here and if you post the question as to the range of voltage and the amount of current, he will probably tell you the answers.

Jack