Charging Deep Cell Batteries

[candidate]

have 360watts panels @ 22volt going through MPPT controller.

get about on sunny day 17amps.

the MPPT I set at cuts out at 14.4volts.

This the bit I am asking the question on?

when MPPT shows 14.4volts and an ammeter I set in system swings back and forth, take it this is the finishing period of the charge.

How long would this have to go b4 fully charged...cus draining 100amps off switches off the power FROM THE BATTERY thru the MPPT, a safety thing.

Batteries are in parallel equalling 400 amps(12volt system)

So from almost flat 10.8volts it would need some how many amps to fully charge, can't be 400amps surely.

A flat battery shud still retain amps at a lower voltage?..surely not starting from absolute ZERO?

I am finding the MPPT achieves 14.4volts after around 8hours which is 15x8=120amps, which is way off 400amps...That's when 14.4 shows and ammeter starts to flicker.

So, when the ammeter flicks and also shows 14.4volts, is this just the last part of fully charging and how will I know they r fully charged apart from a hyd test and volts test...worse a volt drop test which defeats charging them for use.

Or must I do that pin ult latter everytime to check if the batteries are fully charged which seems a pain?

The batteries are always draining off thru daytime of a bout 10watts which runs the BT hub..I am a tight arse I know.

I cud have two sets of batteries I suppose, one with a trickle drain to BT hub and switched off from charging so other bank charges with no trickle discharge, this then allowing a full finish off of battery charging.

 

[Andy™]

batteries do not last forever. every charge and they will hold slightly less. how old the batteries? they may just be dead and need replaced

if the total capacity is 400ah, then it will need 400ah going into it to fully charge... either 10 amps for 40 hours, or 40 amps for 10 hours, or any other combination

one way to see if they are charged is to monitor current going in. once charged / near charged they will take a lot less amps than when flat and charging

 

[candidate]

I feel my problem is that I am constantly draining off some 10watts that would have no doubt a direct bearing of not allowing the MPPT charger from achieving correct charging..

 

[Evans Electric]

All I can say is that Deep Cell Batts don't like being fully discharged apparently , unlike lead acids where fully reversing the electron flow occasionally was deemed to prolong life.  

 

[kme]

Both the guys are right - You need to be measuring the power the PV is delivering to the batteries; over a daily cycle. An ammeter "flicking" isn`t exactly an informative post. 

So your panels should deliver 16. odd Amps @22V; somewhere nearer to 24A @14.4V - peak.

If your batteries can take 400Ah; that would need full delivery from your panels for about 16 hrs - but you`re drawing 10W off them constantly. @12V, thats almost an Amp.

( this is all assuming a lossless system; which it isn`t - I don`t have the off-grid formulae to hand, sorry)

So, if the 10W load is the ONLY load to the batteries; then a bit of maths will give you 23.odd Amps gain, under optimum conditions.

What you need to provide now, is an average daily Kwh production figure from the PV; which is easily converted to the Ah charging of the batteries.

Then your 10W ( approx 1A/hour) load is removed from the batteries; which ought to tell you the net charge/load to the batteries over a given period.

And - the batteries degrade over time, as said  -plus, if one batt has a fault, it can affect the whole bank

 

[brycenesbitt]

Definitely definitely put a cutoff on this system: draining any lead acid type battery to flat greatly affects lifetime.

Only NiCads like that type of treatment.