Trouble with charging a large 12v battery

[Zerax]

That's great, thanks for your time Zerax!
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Thank you for the comprehensive response & tutorial link, Guglielmo. Makes sense. All positive wires leaving the battery terminal are fused appropriately in my setup, including the one going to the MPPT charger. Battery terminals are shielded at all times except when I hook up the mains charger (crocodile clips). This charger is fused on the AC side.

I'll look for a larger charger. If you have any recommendations as to what models are affordable (Ctek's fancy 25A model is beyond my budget) I'll gladly take them.

Cheers

This is one of those areas where it's a classic case of "You get what you pay for"... I'd save up a bit longer and buy quality.

I'm a fan of Victron equipment... not cheap, but it's well built... and has excellent support. Also Mastervolt is excellent... but again... not cheap

 

[UKMeterman]

I have used a £800- £1000 battery bank of large 12V Ah (100, 200) Victron AGm batteries for about 10 off grid PV installations so far. AGM do require their own charging profile to maximise life and make the best use of in my case solar energy. It is important not to overheat the battery during charging so think Isquared R when considering the charge current. The chargers I have used monitor the voltage of the battery and the current and time elapsed to decide when to move to the next stage of charging:

The BULK stage involves about 80% of the recharge, wherein the charger current is held constant (in a constant current charger), and voltage increases. The properly sized charger will give the battery as much current as it will accept up to charger capacity (25% of battery capacity in amp hours), and not raise a wet battery over 125° F, or an AGM or GEL (valve regulated) battery over 100° F.

The ABSORPTION stage (the remaining 20%, approximately) has the charger holding the voltage at the charger's absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger set points) and decreasing the current until the battery is fully charged.

The FLOAT stage is where the charge voltage is reduced to between 13.0 VDC and 13.8 VDC and held constant, while the current is reduced to less than 1% of battery capacity. This mode can be used to maintain a fully charged battery indefinitely.

So the appropriate charger is necessary and have the facility to be tailored to the battery it is charging.

This is one of a few references I used in my research on how to care for these batteries by careful charging and the bold text above is lifted from it:

Battery Charging Tutorial | ChargingChargers.com - http://www.chargingchargers.com/tutorials/charging.html

Important PS: MAke sure you have close to the battery a fuse/circuit breaker to rupture in the event of short circuit and that the battery terminals are shielded with plastic covers.

Be carefull to check the DC current breaking capacity of the fuse / Circuit breaker in this application. There is something to be said for BS88 fuse links in this application.

 

[static zap]

A suitably sized charger may have the opportunity to warm the battery if it is below ,optimum charging temperature !
(I know I struggled to charge a near frozen battery -- Summer time less of an issue ).
Having no warm engine to sit beside !
- my over simplified take - (right or wrong ?)
Do stay safe ..

 

[Lucien Nunes]

My experience of multi-step chargers connected to outsize batteries is that they may not transition from one step to another at appropriate times. One model would get stuck in bulk mode because the current never fell below a threshold. One wouldn't complete the charge because the ultimate timeout for the equalise step was too short for the large battery, another equalised for too long and gassed the battery because the time was computed from the profile of the bulk charge which was longer than the makers had allowed for. You need to know exactly what is going on under the hood, to know the impact of unexpectedly slow voltage change on the charge algorithm. If it's just a standard Unitrode chip driving the process, it's simple. If it's a microcontroller running a proprietary program, there are more variables.

 

[hey-hey-my-my]

Following everyone's feedback here, I've just purchased a Victron 7 stage 30A charger : Victron Blue Smart IP22 Bluetooth Battery Charger - 12V 30A, 3 outputs - https://www.12voltplanet.co.uk/victron-blue-power-ip22-7-stage-adaptive-battery-charger-12v-30a-3-output-uk-plug.html

This coupled with a 400W solar array should manage to look after my 260Ah AGM battery throughout grey winters across Europe.

Can anyone confirm I've made the right choice? On paper it's all good, but I'd like to be 100% sure this model is adapted to AGM batteries. For two reasons:

1) I'm aware that some manufacturers don't configure the End Amps setting correctly for AGM charging, leaving it at 2% (flooded batteries) instead of 4% (due to AGMs having lower internal resistance), therefore overcharging/damaging the battery. This Victron charger has a "high voltage mode" rather than an "AGM mode". There is mention of AGM charging in the manual, but it's almost described like a "once size fits all" charger, which has me somewhat worried now that I've ordered the damn thing.

2) Furthermore, in the user manual, it states the following :

NORMAL (14,4V): recommended for flooded flat plate lead
antimony batteries (starter batteries), flat plate gel and AGM
batteries.
HIGH (14,7V): recommended for flooded lead calcium batteries,
Optima spiral cell batteries and Odyssey batteries.

Until reading this I was pretty sure AGMs need 14.6-14.8V to charge properly.

What do you think? ?
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Another point of concern about this product: in the user manual, they recommend occasionally reconditioning AGM batteries (see passage from the user manual below). I thought AGMs should never, ever be reconditioned!?
My battery has indeed stayed below 80% for over three weeks due to the weak mains charger & insufficient solar power. Would you recommend a "reconditioning" cycle as Victron suggest?

"A lead-acid battery that has been insufficiently charged or has
been left discharged during days or weeks will deteriorate due to
sulfation¹. If caught in time, sulfation can sometimes be partially
reversed by charging the battery with low current up to a higher
voltage.
Remarks:
a) Reconditioning should be applied only occasionally to flat plate VRLA
(gel and AGM) batteries because the resulting gassing will dry out the
electrolyte"