I noticed something interesting today after our battle. I have 4 LiPos in my Bismarck. 11.1v, 5200 Mah batteries. I tested each battery when I got home and found that two were drawn down and the other two were still full. Two batteries were at 3.62v/cell and two batteries were at 4.1v/cell. I checked all of my wiring individually and all four of the connectors supply power to the entire system. So I am pretty sure that there aren't any wires disconnected causing this. Any ideas?
You may have a series resistance in line with the higher voltage cells or their internal resistance is much higher than the other pack pair. A corroded or worn connector could do something like this. Do you know your current draw overall?
I have 0.1 resistance (at 200 setting) on the positive and negative side of the harness across all connections.
How much did you run the boat? If it wasn’t much (just drive around the pond a bit), then total discharge could be very low. The voltage vs state of charge curve for lithium batteries peaks just before hitting 100%, and is relatively flat for most of the discharge range, so 3.6 is not necessarily much different than 4.1. If you are concerned about a connection, I would try running the boat off each battery one at a time, plugged into the different plugs.
I used the same 4 batteries all day. 4 sorties worth. There was no noticeable changes in performance to the boat on the last sortie. So your suggesting trying one battery to one terminal connection. My current setup is two batteries to one connection for both sets of batteries.
For lipo's, 3.6V under no load is way down, near the proverbial cliff at empty. It sounds to me like either the cells are grievously mismatched in internal resistance or you have a wiring issue somewhere. if you knew overall current draw we could guesstimate the under load characteristics to help you find it, but my money is on your wiring harness. if you assume your pump is the primary consumer, ohm out each terminal to the correct terminal at your pump's ESC. both positive and negative. if you are always getting the same value, set your ohm meter to a lower range. If you still can't measure any difference, let me know what ohm meter you are running and I can see if mine has higher resolution, and you can try it.
The pump is right across from the batteries that were drained down the most. I just found something interesting. I put a storage charge on all 4 batteries. After measuring them just now with a meter, all the batteries were at 3.8v/cell. However, 2 batteries read at 44% and two batteries read at 60%. I am currently balancing the two 44% batteries. Figured it might help.
there is one other thing to keep in mind... do you happen to run all the positive lines on one side of the ship and negative on the other?
It would help if you could share some pictures of the wiring. It seems like one pair either wasn’t plugged in or only powered something like the solenoids. Given the run time I would expect all batteries to be discharged a decent amount so I would lean towards wiring issue rather than battery defect
2x that. Can you send a picture of the as installed layout as well as take the cable harness out of the boat. Lay it out flat so we can all see how it's wired together
Apologies in advanced for the childish drawing... I am not 100% but I think the batteries on the feed wire directly across from the pump were the ones that were drained down.
Have you checked continuity from each battery connector to each load connector, for both negative and positive? One of the screws could be loose. the connecting metal piece between all of the terminals could also be much higher resistance than the resistance from one side of the block to the other, preferentially pulling from one battery pair vs the other (I would still expect the one set with low discharge to be discharged more) many folks in the NE use xt bus bars like this for power distribution. SJS is coming out with waterjetted copper connecting plates soon
I've seen that design floating around the forums. Do you have an issue with current jumping across and shorting out the system when its submerged in water?
No. The soldered side is potted in epoxy which insulates the connections. On the plug side, I always have a plug in each connector, either to a source/load or a dummy plug if that connector is not needed
OK. So you solder them all together and then put the wired portion in epoxy. The same way you would to waterproof a receiver?
