Ok, so if my batteries are at 52v and I want to charge them on a cloudy day, I turn on my generator which is 4.5kw via the ATS/VRM.
My multi is a 48-3000-35-50, so can only accept an input amperage of 8, which equates to about 1500w max coming from my generator.
However, before I turn on the generator, I notice the battery voltage at 52v, the generator goes on, it pushes out 58v, the multi immediately goes in to absorption and reduces the load from the generator to 600w! And I’m just wanting to charge the batteries up as quick as possible.
Is there any way for the multi to distinguish the difference between the actual battery voltage (that needs charging) and the voltage coming in from the generator?
13V is the idle voltage of a lead battery.
If you try to charge a full battery the voltage goes up quickly and the charger will quickly switch from bulk to absorption/float and reduce the current.
Older batteries can sulphate, and be slower to accept charge. This can account for the rapid rise in battery voltage when the generator starts to charge. Yuo would expect the Voltage to rise by 2-4V when they start to charge, 6V seems to be very high.
Absorption voltage should be about 55.2 (13.8 / 12v block) and float around 52.8V (Depending on manufacturer’s reccomendation & temperature dependent.).
If the battery voltage is not rising when a charge is being applied to them, then there is a problem with the batteries.
They may be sulphated or buged or have bubbles in them near the plates preventing charge.
There is technically nothing wrong with the inverter (unless you have verifirled with a meter) that at the inverter terminals that is not the voltage it is saying that it is.
Hi Lx, I think you have that slightly wrong, with a sulphated battery, if you apply charge the voltage rises immediately to Abs voltage, and only a low charge current is passed. OK, when you remove the charge voltage, the terminal voltage will immediately (5 min) drop back to the original voltage. This is due to the increased series resistance of the cell. Yes the cells will bulge, and also get hot.
@The Nook, 55.2 is the low end of the Abs voltage range, for some battery types it can be as high as 59.2. How often do you equalize the cells? It does not look like there is any problem with either the multi or the generator, but in the batteries or battery cables.
Had a set once where the batteries did not change voltage at all. So not entirely out of the realm of possiblity. They were agms though not gel. So that may have been the reason.
On gel it is also possible to have them stuck at 13v as well so no charge ior discharge possible.
So where do I see the real voltage level when I turn on the generator ?
So, for example, batteries at 56v, then generator goes on, the voltage goes up to 58v, I then turn the generator off and the voltage goes back to 56v ???
To measure the true voltage of the batteries, you need to let them stand with no load or charging for 1 - 4 hours.
With a lead battery in good condition, the voltage will only rise by 1 - 4V when charge is applied, then the cells start charging.
The Way to check: if the initial voltage rise is too high, and the charge current much lower than expected, then there is excessive resistance in the charging path. This may be due to long wires of insufficient size, corrosion on terminals or poor crimps - or internal corrosion in the battery - including sulphation which reduces the effective plate area.
You did not comment on how old these batteries are? All batteries have a lifetime measured in years, and also a limit on the number of kWh that can be cycled through them. Under-charging lead batteries can also lead to early sulphation. Sometimes this can be reversed by an equalising charge, but this does not always work. If the batteries are more than 3 - 5 years old (depends on type) then age is affecting the capacity.
The true state of the cell cannot be measured by voltage alone - especially not under charging conditions. To get the true state of the battery, it must be fully charged, and the acid concentration checked with a hygrometer - impossible to do with VRLA (AGM) or other non liquid electrolyte.
They charge to 100% when the sun is out, with no problem at all.
The very basic problem I’m having is that I simply want to see the correct voltage of the batteries whilst the generator is on.
When the generator is on, it falsely increases the visual voltage on all devices to the amount of power it pumps out (57v). I don’t want to see this, I want to the the battery voltage slowly increasing as they get charged by the generator
If the shunt is by the batteries this should be happening automatically unless there is a very high resistance connection between everything.
The voltage at the inverter terminals has to be high to encourage power flow it must raise the potential to create that. This would be normal as you ultimately want the batteries to charge up that high.
Did you verify anything the a digital multi meter?
There are a few widgets you can load on the vrm (or combine them with the ai assistant) voltage from the mppt terminals, voltage from the ve bus terminals and voltage from the shunt.
