I have a bank of two 12 v batteries connected in parallel. Apart from the two connector cables between the batteries, there are connections to loads or chargers on each the 2 positive and 2 negative battery terminals. Judging by the different cable diameters, these connections are in pairs and diagonal across the battery bank, so all OK.
Now, to install the BM shunt, and for the Battery Monitor to function, I need to place all the negative connections on the single “loads and chargers” terminal of the BM shunt and to connect the battery bank negative to the other terminal of the BM shunt.
Question: having moved all negative connections to a single point, should I also transfer all the positive connections to the single battery bank positive, so that all loads or chargers connections are once again diagonal on the battery bank, and the equilibrium of the two batteries is maintained?
Thanks for your help.
Yes, move them to the same point. Even the low resistance of paralleling wires can have an effect on battery balance. Do it properly…
I have a similar (probably rookie) question. I have two 12 v batteries connected in parallel with jumpers. I understand all negative load and charging cables will get moved to the appropriate side of the shunt.
On the battery only shunt connection, does the jumper matter? Or since the batteries are in parallel, will the BMV “see” only the 12 v? Also, if I need to connect only one battery to shunt, do I connect other battery to charger and load side of the shunt? How do I get back to parallel?
You need to leave the jumpers in place.
You must move all negative battery connections to the “charge and load” side of the shunt. Then you need to bring together all positive connections on the positive of the OTHER battery younegative of one battery, via the shuntll négative connections to tpo
Sorry, jumped the gun. See below
You need to leave the jumpers in place.
You must move all negative battery connections to the “charge and load” side of the shunt. Then you connect the battery side of the shunt to the negative of one battery. You need to get a lead made for that, and it is advisable to get one of larger diameter than the largest presently connected. Then you need to bring together all positive connections on the positive of the OTHER battery. This is because the jump leads have a small but significant resistance, relative to the internal resistance of the batteries. With the above configuration, each battery is connected to the loads and chargers via one jump lead only.
To do otherwise would place two jump leads in the circuit of one battery, and none on the other, so one battery would be charged more than the other. Unequal charges and loads can / will damage the batteries and overcharging one can be dangerous.
PMS
Wire them like this. If what you call jumpers are the wires between batteries, a better term is interconnects.
Thank you! This is how I was planning to do it, but didn’t know the ramifications, if any, of the interconnects. And thank you, interconnects is indeed what I miscalled “jumper”.
Thank you. If I understand correctly, this is in effect what PWFarnell illustrated for me as well. My concern was how the interconnects would be seen by the system, if at all. I will connect positive of bat 1 to + loads and chargers, neg from bat 2 to batt only side of shunt, and - loads and chargers side of shunt to - loads and chargers.
(Sorry for the poor illustration. From me, that’s as good as it gets.)
A small, but potentially significant, modification to parallel battery block cabling.
The use of terminal bus bars (TBB) permits electrically identical connections to each block, promoting true parallelism.
A ve+ and ve- TBB will have balanced distribution. (No need for + at top, - at bottom, wiring in an attempt to mitigate the inherent unbalance of “daisy chain” interconnects.)
In the illustration, an intermediate ve- TBB is used to balance an arbitrary number of parallel branches (try to keep at no more than 4) before connecting to the “battery side” of the monitor shunt. With only 2 battery blocks, their cables can be stacked onto the shunt’s battery terminal, eliminating the intermediate TBB.
Completely agree, the perfect solution with two batteries is with 2TBBs and 2 pairs of identical connectors to the batteries. I am also in the process of connecting a Victron battery monitor and am going to shift to the 2 TBB solution.
For 2 batteries I would dispute it being a significant benefit, as long as the interconnects are sized properly, the opposite corner wiring method gives equal resistances to both batteries. Once your are at 3 or more batteries, the bus bar has benefits. For 2 batteries it has the downside of more crimps and bolted connections, more contact resistance and more connections at risk of vibration in a mobile application.
OK Many thanks for that. I think that may be why I had thought to just do an opposite corner solution, much simpler, less potential sources of (unequal) resistance. So opposite corner in the end…