My Multiplus Compact 24/2000/50 will be connected to a machine that runs on 24v and discharges the batteries with a fairly high current for short periods, maybe 2 minutes at a time. I previously had two separate 12v chargers, one on each battery, which has been fine apart from blowing one of the chargers one time (a non-Victron charger). Anyway, doing some quick tests today I can see that the voltage of one battery was a good bit higher than the other after a 1 minute (discharging) operation and I am wondering if the 24v charger is actually a good idea for these two 12v batteries or whether a VictronBattery balancer or two could make a big difference. After the operations the batteries usually have several minutes of “rest”, or uninterupted charging and at the end of the day they are left to charge for a couple of hours.
Basically my question is would a/some battery balancers with a 24v charger be able to keep two not entirely matched batteries in good health or should I go back to two separate 12v chargers ?
If they are lead-acid batteries, that may not be enough. Can you see what the voltages and currents are just before the cut-off? Balancers are unlikely to help much there. Two chargers with suitable voltages would probably be better.
You mean charging afterwards for a few hours may not be enough ? That I can remedy, I can leave them on charge for as long as it takes. My concern is during the work period - will charging as 24v kill the weaker battery, of the two batteries in series, more quickly than with two separate 12v chargers ?
What’s the actual peak load (amps or watts), and duty cycle (discharge vs charge time)?
What do you have for batteries, specifically, and how are they set up?
e.g. two 12V 100Ah AGM lead acid batteries in series (that’s a total of 24V, 100Ah capacity - so am guessing you have either parallel sets like this, or higher capacity as the Muliplus is going to need 200-400Ah of capacity).
The Victron Battery Balancer is good for only up to 1A current on its own, to deplete the higher-voltage battery in a pair, so if you use it with an additional charger beyond what the MP can provide, you may need to put a few BB in parallel to achieve what you want.
I know it’s a bad set-up but it’s two 70aH flooded, basically car starter batteries, in series. The load is an hydraulic pump that draws around 150 amps and is usually used in bursts of 10 seconds to 2 minutes and may have a minute or as much as 15 minutes between bursts.
Whoa. That’s just gonna kill the batteries. More homework needed for you my friend!
Is 150A the startup current on the pump (eg its usually 5-8x the running current), or the actual measured running current?
If you’re thinking of using the MP as a 50A charger, you can’t charge the batteries fast enough safely - e.g. safe charge rate is about 10% of the Ah rating = eg 7A. Pushing it to 14A, the batteries will heat up and start gassing, so they have to be monitored. If they get half depleted (about 30Ah used in an hour), it’s gonna take 2+ hr to charge them backup.
So you’re gonna need more battery capacity - or switch to LiFePO4 as they can be charged quicker.
The correct batteries would cost a fortune, I’m skint.
The batteries that I have do get abused but similar to in a car starter circuit where they will give hundreds of amps for a short duration. Then they could charge at somewhere around 25 amps via the car’s alternator (and car batteries live for 5 years or more). I know a car starter will only work for 3 seconds at a time in a healthy car but start-stop vehicles can be doing that several times even in one minute.
I know what I have is a bad set-up but to keep it as healthy as possible I have two choices: get one or more battery balancers and stick with the 24v charging or go back to the two separate 12v chargers. Knowing my system what would you do - go back to the separates ?
With no budget, it’s a tough question. 24V charging and a balancer is relatively inexpensive. Balancer will help get things back to balanced during off-hours.
Here’s another idea that’s inexpensive:
Add a SmartShunt 500A which you can monitor with your smartphone. It can measure the battery current, the total 24V, and the midpoint between the two batteries (12V) so you could tell if still out of balance, and this would give you some historical data too, which would help you figure out what is actually going on.
And if they are out of balance (very likely), what to do on a budget ?
While operating the hydraulics, the charger is more like a power supply giving max current and then after the high current, it will tail off over the next few minutes recharging the batteries. During these operations in (“power supply” mode) I don’t think any imbalance can be “fixed” so we could forget that as a goal, but if I could avoid damage caused while in charging mode that would be a good step. Are a couple of battery balancers enough ? My measurements yesterday showed one battery at 14v and the other at 15.5 just after using the hydraulics although that difference would reduce after a while but for the first few minutes after each operation it would be a big difference.
If not, I’ll resell the multiplus and go back to separates.
Why that?? It still doesn’t solve the problem of placing a heavy load on the battery bank, so the effects will continue to occur.
If I were you, I’d install the shunt and, if necessary, fit a balancer to monitor the situation, while keeping an upgrade to Li in mind for all future purchases (the shunt could continue to be useful with a 24 V Li battery with an internal BMS).
P.S.
During my brief tests with a 24 V MP 3000, I connected two conventional starter batteries of approximately 50 Ah in series and charged them with the MP while limiting the charging current. The balancer had to support the older, neglected battery.
Connect a 12V charger to the battery with the lower voltage at the same time. Batteries take a very long time to become fully charged. If they are not fully charged every day, they will gradually sulphate. In a series connection, the battery with the higher charge will be overcharged. If they are flooded batteries, they will use up water. It is important to know what type of batteries they are. If they are EFB batteries, that is not a bad thing.
Placing a heavy load on the battery bank is unavoidable, it’s just the way the machine works. My need is to charge the batteries with the least “wear and tear”. I do lots of monitoring and I already know that the batteries are not matched and more monitoring won’t help that. Having used battery balancers, how well did they work ?
Those are certainly the readings with the hydraulic pump switched on. Above, you said that after switching off the hydraulic pump, the batteries are at 14 V and 15.5 V. That is due to the high charging current. But I asked what the voltages and current are after about five hours.
not good on the long term with too small batteries (you have some information about battery design and size in the manual)! My use case was to configure the Mp on site without the battery (it was still on delivery), so i used some car batteries.
you will need the suitable lead or LI battery and the appropiate charging (you can limit the MP in case of a lead bank and using the lead charging curve)
I know you are right but I need the full current of the MP as this is also effectively a power supply when the machine is operating. If it could give the full 50 amps while machine is operating (voltage under 24v for example) and then quickly reduce as soon as the machine stops (perhaps voltage over 25v) so actual charging is more gentle in the first minute. Don’t know if you can create your own charging algorithm ?
It may be that the batteries have lost water. Does one battery have a higher voltage while charging and a lower voltage than the other while discharging?
Yes, to keep the voltage at 13.8 V for many days, if it is sulphated.