I've just put together (2x) 12v 100ah LiFePo4 in parallel, coupled to a 1000w inverter, all Renogy and using 4AWG. All cables/fuses/shunt etc were factored in to give equal lengths(massive assumption that resistance is the same lol). I took the feeds to the inverter one from each battery to equalise the demand on them but what I found having to fully charge them to set the Renogy battery monitor(with a Renogy 20A charger, they were at 13.1v) using the same method (one crocodile clip on each battery) was that they charged to 13.7 and just stalled, the red light never turned green and it stayed like this for an hour-and I'd checked this with the multimeter. I separated and charged both batteries individually, only took 10 mins to hit 14.6 on each and the green light came on. I then removed the charger and coupled them back up again and the voltage had started dropping (I assume down to "float"?) and at 14.0 I put the crocodiles back on but this time only on the one battery, and the charging went complete again with me monitoring the voltage with the multimeter on both batteries!! Seems something is not liking the "dual battery charging" but is ok with one being used and both hitting same voltages? Any ideas what may be the reason behind this? I was concerned I either had a duff battery or charger but this cannot be the case. And a 20A charger should be enough for my combined 200ah given a 10A charger is sold by Renogy and that would be ok for one battery (100ah)? Oh, I'm still discharging from the dual terminals as that's how it's been sized and wired!
I'm not quite sure how you are wiring this. When you say one clip per battery are you saying 4 total which is 2 for positive combined to the positive on the inverter and same for the negative? Normally we use wires or buss bars to connect positive to positive and same for negative when wiring in parallel. In any event, charging the 2 at the same time results in double the time to fully charge. If the 2 batteries are not matched - say one is failing, then it will consume energy from the better battery.
@@MyEngineeringProjects Sorry for the confusion- cables- so pos to pos and neg to neg short cables. The inverter gets the pos from one battery and neg from the other battery so the closest one isn't doing more work than the other and to try an balance the two as best as this allows. Buss bars would no doubt make that more accurate!
Ok now I see how you are doing it. Even if you use the same size charger, that's ok, it just takes a bit longer. I'd let it charge all the way up to the top and see what happens. When you charge any battery to the top then remove the charger, it's totally normal for the voltage to drop immediately. It will then settle down to the rest voltage. What would be a problem is that if they kept dropping and never stopped. This would be indicative of a bad cell somewhere.
What if you turn one battery opposite to the other and connect diagonally pos to pos neg to neg would be any better than just the reg way of connecting batteries in parellel ?
That's essentially how I wired it when I moved the positive power lead to the opposite end. In this configuration, the power connections are diagonal across the battery pack. This is a good solution.
In practical terms, by improperly connecting load, to batteries in parallel, it will increase voltage imbalance, between the individual cells. This leads to faster separation, of cell voltage, which equals quicker cell failure, especially when there is a series connection, and/or with the use of older cells.
Looks to me that the cross connects are such minimal gauge that there is a guaranteed imbalance. With proper 1/0 AWG between the terminals, I strongly suspect the issue goes away....
The batteries have a maximum current of 20 amps and it limited to that by a BMS. A #10 wire for chassis current can handle more than 20 amps (it's only 2 inches long). It is true that the smaller the wire between batteries the more you will see current differences when wired incorrectly. However, even with a buss bar, it's still recommended to not take off power from just one end but instead distribute it evenly.
Your red jumper wire look chunky enough and about 6 inches long. It is hard to believe hooking the charger to one battery terminal or another will make much of a difference charging the 2 batteries.
Yes it is surprising. That's why I wanted to measure it to verify what the problem really is. Current will follow the path of least resistance and the wires definitely matter, even though they are short.
Looks like a 'busy' workshop..! Just as it should be. 👍 Thanks for the video.
Yeah I have a lot of projects going on at the same time. I need a bigger shop.
I've just put together (2x) 12v 100ah LiFePo4 in parallel, coupled to a 1000w inverter, all Renogy and using 4AWG. All cables/fuses/shunt etc were factored in to give equal lengths(massive assumption that resistance is the same lol). I took the feeds to the inverter one from each battery to equalise the demand on them but what I found having to fully charge them to set the Renogy battery monitor(with a Renogy 20A charger, they were at 13.1v) using the same method (one crocodile clip on each battery) was that they charged to 13.7 and just stalled, the red light never turned green and it stayed like this for an hour-and I'd checked this with the multimeter. I separated and charged both batteries individually, only took 10 mins to hit 14.6 on each and the green light came on. I then removed the charger and coupled them back up again and the voltage had started dropping (I assume down to "float"?) and at 14.0 I put the crocodiles back on but this time only on the one battery, and the charging went complete again with me monitoring the voltage with the multimeter on both batteries!! Seems something is not liking the "dual battery charging" but is ok with one being used and both hitting same voltages? Any ideas what may be the reason behind this? I was concerned I either had a duff battery or charger but this cannot be the case. And a 20A charger should be enough for my combined 200ah given a 10A charger is sold by Renogy and that would be ok for one battery (100ah)? Oh, I'm still discharging from the dual terminals as that's how it's been sized and wired!
I'm not quite sure how you are wiring this. When you say one clip per battery are you saying 4 total which is 2 for positive combined to the positive on the inverter and same for the negative? Normally we use wires or buss bars to connect positive to positive and same for negative when wiring in parallel.
In any event, charging the 2 at the same time results in double the time to fully charge. If the 2 batteries are not matched - say one is failing, then it will consume energy from the better battery.
@@MyEngineeringProjects Sorry for the confusion- cables- so pos to pos and neg to neg short cables. The inverter gets the pos from one battery and neg from the other battery so the closest one isn't doing more work than the other and to try an balance the two as best as this allows. Buss bars would no doubt make that more accurate!
Ok now I see how you are doing it. Even if you use the same size charger, that's ok, it just takes a bit longer. I'd let it charge all the way up to the top and see what happens.
When you charge any battery to the top then remove the charger, it's totally normal for the voltage to drop immediately. It will then settle down to the rest voltage. What would be a problem is that if they kept dropping and never stopped. This would be indicative of a bad cell somewhere.
What if you turn one battery opposite to the other and connect diagonally pos to pos neg to neg would be any better than just the reg way of connecting batteries in parellel ?
That's essentially how I wired it when I moved the positive power lead to the opposite end. In this configuration, the power connections are diagonal across the battery pack. This is a good solution.
@@MyEngineeringProjects ah very good
In practical terms, by improperly connecting load, to batteries in parallel, it will increase voltage imbalance, between the individual cells.
This leads to faster separation, of cell voltage, which equals quicker cell failure, especially when there is a series connection, and/or with the use of older cells.
Yes it sure does
Bus Bars - FTW!
Buss bars are the best
Wrong electricity takes all possible paths.
Looks to me that the cross connects are such minimal gauge that there is a guaranteed imbalance. With proper 1/0 AWG between the terminals, I strongly suspect the issue goes away....
The batteries have a maximum current of 20 amps and it limited to that by a BMS. A #10 wire for chassis current can handle more than 20 amps (it's only 2 inches long). It is true that the smaller the wire between batteries the more you will see current differences when wired incorrectly. However, even with a buss bar, it's still recommended to not take off power from just one end but instead distribute it evenly.
Your red jumper wire look chunky enough and about 6 inches long. It is hard to believe hooking the charger to one battery terminal or another will make much of a difference charging the 2 batteries.
Yes it is surprising. That's why I wanted to measure it to verify what the problem really is. Current will follow the path of least resistance and the wires definitely matter, even though they are short.