G’day.. I have the MTTP Ve.can 250/100 charging a battery bank. The battery are all Bosch and according to the data sheet the initial charging current has to be less than 36 Amp.. The MTTP can go up to 100amp…
My question is: is the Max charge current in the setting related to the entire bank, as in 36 amp for the lot or I have to keep in consideration that the battery are also in parallel and therefore I actually can go as high as 72 amp (24 volts banks)?
The issue with the low Max current charge is that in the middle of the day if I use an appliance that need say 1.2 Kw, the solar only gives me around 700 watts where if I select 100Amp I can get up to 2.0 Kw… Does it make sense?
Can anyone suggest the best way to keep the battery healthy and still been able to use high power appliances…
Thank you
Do you have a cerbo GX? You can use DVCC to adjust the charge current, do it manually or do something with node red to say if the inverter power X set the charge current to X.
In a series system all components will see the same current so the 36A charge current is correct ea battery will charge at 36A or 36Ax28V ~ 1000W.
If you use a current clamp or the battery bms to see the current you should see half the MPPT charge current if they are in parallel. The only time you will see the max charge current say the 72A you want to set it to is if one BMS disables charge the full charge current will go to the battery that is still accepting charge.
That is if you are using lithium with a BMS. Not sure what chemistry you have.
Thank you again… Forgive me but I’m old and perhaps I haven’t explain myself properly…
When my MTTP is set to 100Amp in the settings, I can see 2.0kw coming into the system.. I have just replaced the battery banks with 6 new 12 Bosch AGM… I was just wondering if the setting in the MTTP (MAX Charge Current) can be left on 100Amp or I have to come down to the 36Amp recommended by the battery spec sheet… The question is: because I have the battery connected in parallel, does it mean that I can double that 36 Amp in the setting and set it to 72 Amp? there is nothing in the manual and I cant find any literature on this subject…
When batteries are put in parallel you can set the charge amps to the “mfg charge amps” x # of batteries in parallel. However, let’s say that you have a battery that can take 10 charge amps and you have ten of those batteries. The 250/100 solar charge controller can charge at 100 amps and could run at spec with that battery bank. However, you probably would want to use a lower charge rate, say 90 amps.
With LiFePO4, as a battery hits the high voltage limit it cuts off the incoming current. That causes the rest of the batteries in the bank to have more current available to them. AGM doesn’t have the ability to cut off the charge current, so the current is more likely to stay shared among all the AGM batteries in the bank. The solar charge controller will watch the voltage and throttle back as the voltage rises. This is greatly oversimplified, of course.
The more AGM batteries in the bank, the more you have to manage the batteries. A balancer may be appropriate. Set the solar charge controller for your desired charge current and then check how many amps are being put into each battery at various stages of the charge.
Wiring of the batteries in such a large bank is very important. Look up the Victron Wiring Unlimited document.
Sorry let me clarify.
If you stayed at 12v then 2 batteries is 36A x2.
With 24v it remains 36A of current.
It is more now an engineering question.
All power is on Volt Amps (VA)
You can increase amps if there is parrallel as well and good current sharing on the battery bank.
I used your example questiom in your post. I see you have more than that.
How you wire it matters. Wiring unlimited is a neat layperson resource.
Just to be sure I understand… The Bosch battery have a 36Amp max charging, so I can setup the MTTP for 72 Amp and it is OK for the battery… (or in my case x 3 parallel 100Amp)
Are you 100% positive about this and did I understand correctly?
To me, it makes sense as I setup 360 Amp in the BMV setting, so I originally thought that the Amp charging would have work the same way, but I just wasn’t sure of it…
I had two 280 Ah LiFePO4 batteries in my prior camper that could accept a total charge current of 280 Ah (.5C, which is normal for that battery chemistry). None of my chargers (individually) would go that high. But add up the Multiplus (120 amp), the two MPPT 100/50 and a MPPT 100/20 and my current could theoretically hit 240 amps. In practice it would never be that high, but the battery bank wouldn’t have complained.
My two batteries were well balanced so they both hit 100% state of charge at about the same time. If they were not balanced and one of the BMS cut off the charge due to high voltage (14.6v), and I was charging with 280 amps, the BMS in the other battery could see the full amps, which could have shut it down due to over current.
I use the Victron default charge parameters for LiFePO4, so my bulk is 14.2 volts and float is 13.5 volts. Your approach for lead acid batteries will be different.
Been able to set the MTTP to 100Amp gives me the choice to run high wattage appliance during the day when the solar panels can output up to 2500 watts…
Two 12V batteries in parallel, the voltage stays the same 12V, but the current capacity Ah or A draw doubles. So, if each battery is rated for 36A of continuous current, two in parallel would charge at 72A at 12V.
With two 12V batteries in series, the voltage doubles 24V, but the current capacity remains the same. So, if each battery can charge at 36A, the total would still be 36A at 24V.
