Voltage alarm setup for Lipo batteries in series

[tjmartin]

I am currently wrapping up a new quad build where the ESC's will be for 3-8S Lipo batteries. It's easy enough to connect to 3S or 4S batteries in series to accomplish this. How do I connect two Lipo batteries in series to a voltage alarm? Do the balance plugs get put on side by side or is there an adapter than needs to be made?

 

[Craftydan]

Since the lowest pin on the high pack is electrically the same as the highest pin on the low pack, you'll need to make an adaptor.

so you'll have:

Battery - Monitor
4---------------8
3---------------7
2---------------6
1---------------5
0-----\

>--------4​

4-----/
3---------------3
2---------------2
1---------------1
0---------------0

I suppose it goes without saying, make sure you plug them into both the power and balance series adaptors in the correct order . . .

 

[tjmartin]

Thanks for the response Craftydan. I figured this would probably be the best route of action as well. Basically I need to make a Y connector to go from the balance plugs into one header in the proper order of course and that one header would plug into the voltage alarm. Do you happen to know what these connectors are called exactly so i may make them?

 

[RichB]

Why not just use two voltage alarms, plugged into the two balance leads?

 

[tjmartin]

I had not thought of that and the more I think about it, I do not think it will accomplish the main goal. I will be combining 2 3s batteries for a total of 22.2v presumably. Wouldn't we want to monitor the total voltage and not the individual? I may be wrong in this thought but is my best guess. I have never had a need for this yet.

 

[Craftydan]

the socket/plug you're thinking about is the JST's XH connector:

http://www.farnell.com/datasheets/5448.pdf

Plenty of hobby shops sell the pigtails of these as "balance connectors", and many electronics destributiors like Farnell or digikey will sell them as well, but I'm not sure of their minimum order (unless you *want* a real of 500 . . . ).

They're good plugs, but If you're careful with the polarity, you can use a 9 pin Female 100 mil header, and a pair of matching 5 pin 100 mil male headers.

. . . or you could just go with two lipo alarms as Rich suggests. If you need 8s battery, I doubt you'll notice the extra weight.

 

[Craftydan]

I had not thought of that and the more I think about it, I do not think it will accomplish the main goal. I will be combining 2 3s batteries for a total of 22.2v presumably. Wouldn't we want to monitor the total voltage and not the individual? I may be wrong in this thought but is my best guess. I have never had a need for this yet.

Actually it's better to monitor the individual cells. Especially in the higher count packs, if one cell begins to go bad near the beginning of the flight, the total voltage can still be in the "safe" region. If all the cells are still running in the safe region (>3.3v/cell) the total voltage can't help but remain good.