Many days ? Ok i will do that.
You need the MK. 3 and VE Configure for that, and you should know what can and cannot be done.
But everything depends on the lead-acid batteries — they’re the bottleneck! There’s no point if they also fail in a short time!
You need to provide more capacity, or build a lithium-ion battery from individual cells plus a BMS, or obtain a ready-made 24 V battery (it doesn’t have to be a Victron Smart one; the BMS should be able to handle the maximum current).
The Lithium would be for the future but now I’ve only got half-knackered car batteries.
Anyway, thanks for your help.
Then get more scrap car and truck batteries, plus one or more balancers.
Just tested volts after being on charge for about an hour: first they were 14 and 15.5 then they go down and down and just now they were both 13.20. At that point charge current was minimal.
Edit : A quick secondary question: If I was to create a custom charge algorithm to allow full current but quickly trim it back as soon as a certain voltage was reached, to basically give full current only when the machine was operating, what parameters and voltages would you suggest ?
The high voltages are because the charger is in the bulk phase. But 13.2 V is far too low. That means the charger is in the float phase, or it’s switched off. Check this and set the float voltage to 27.6 V. Then post the readings again after a few hours.
What still bothers you about continuing to use two separate 12V chargers? Isn’t that the simplest way?
Well, nothing really but I have one victron 30 amp and one Kisae 40 amp charger which used to be one of two but the other burnt a mosfet. My thought has been that If the second Kisae goes the same way as the first I will get another Victron 30 amp but then I saw this 24v Multiplus at a good price and thought that would charge both batteries and I will have spare chargers to keep in reserve or sell.
The problem will
The problem is that the 12V chargers will be combined as a 24V power supply when the batteries can’t provide full currrent to the pump, and the supplies probably don’t have sufficient internal protection, especially if there is a back-current when the pump stops, so the outputs will blow.
Maybe that is what blew the mosfet on the second Kisae charger. This set up has been working for 2 years although it may get used only once every couple of months for a day or two.
In theory when the machine operates and the chargers are at full current it is just the same as connecting a charger to a very flat battery and the charger should be able to cope with this or it wouldn’t last long in the real world.
I don’t know whether there is any back-current from the pump, but that would then be a general problem.
The 12V chargers don’t know that the batteries are connected in series — I think that’s the best solution.