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joey avatar image

Charging bank simultaneously with two chargers

We have a Lister-Petters TR3 with Stanford 16.6kW generator charging a 24v 1150ah AGM bank with a Multiplus 24/5000. At max charge (120amp) and daily load demand, we have difficulty achieving a constant high SOC. Could we utilise the genny better by having an additional 120 amp charger in conjunction with the Multiplus 24/5000? The +/- leads from Multiplus to bank are 100mm2 x around 4 meters long. Thanks, joe

battery charging
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joey answered ·

Hi again Justin,

I meant to mention that at bulk charge mode, the multiplus is only charging at 26.5v. At factory settings, I thought it should be charging AGM batteries at around 28.5vand 27.6v at float mode.

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Hmmm yes that's rather odd, at default settings it should be bulk/absorption charging at 28.8v and 27.6 float, at least according to the manual... where did you acquire the unit? I'm thinking that perhaps your distributor changed the charge settings before shipping to you or something like that, but the likelihood of a distributor doing that without some direction to do so is pretty bloody slim.

Another question is how old the unit is, as it's very possible that the default settings are different on the older units that I'm not seeing a manual for.

joey avatar image joey Justin Cook - Bay Marine Supply USA ♦ ·

Hi Justin, my apologies for the delay getting back to you. We purchased the unit from the Victron distributor here in Ireland just a couple of months ago. I asked him at the time were the factory settings compatible with the AGM bank, and he confirmed they are. I did mention to him that the battery temp sensor wire isn't long enough to reach the bank negative. He said it would be ok to leave it disconnected. Rgds, joe

@joey, well the good news is that your distributor is technically totally correct; the default settings are totally compatible with the AGM bank, as it is a default AGM profile. And in reality, there's no harm at all in charging at 2.3v lower; it's entirely arguable that this will actually increase the life expectancy of your bank by a few cycles over the course of time... so no harm there, particularly, I'm just confused as to why it's charging at a lower voltage than it should technically be set for. Now, just to confirm, where are you measuring the stated charge voltage of 26.5v?

If you're measuring that charge voltage at the battery bank, and the battery bank is 8m round trip away from the MultiPlus, then you're most likely just seeing the voltage drop over that great of a distance, which is unfortunate but to be expected... if you're seeing that voltage at the Multi side, though, I'm back to being curious as to why that would be.

joey avatar image joey Justin Cook - Bay Marine Supply USA ♦ ·

The 26.5 reading was taken at the Multi side. At the moment the bank is located in the ship engine room, and the Multi in the adjacent utility room. As so as we get time, we intend to move the bank into the utility room so the cables will be reduced to around one meter.

joey avatar image
joey answered ·

Hi Justin, thanks for advise. I am a Mech Eng and flying blind when it comes to electrics. Really appreciate it. Kind regards, joe

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@joey, absolutely. Parallel charging a bank of that size only makes sense; technically you can pretty much hook up as many chargers as you like to the bank, so long as you don't exceed the manufacturer's recommended charge current... realistically for a bank of that size, I'd think you'd want to be charging around 250-280A, so if you're running two 120A chargers that at least puts you in the ballpark.

Also, for obvious reasons, you want to keep your charger output as close to the actual bank as possible to minimize voltage drop... 4m is 8m round trip, which is a long bloody way... though you do have the cable to deal with it, but if you can possibly mount a second charger closer to the bank, that'd help you out pretty significantly.

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