What voltage should my new 'smart charger' maintain the batteries at?

[Mistroma]

Hi Mistroma

Thank you for your thoughts. In normal everyday day use the batteries are only asked to support a single Johnson 5.5 amp water pump along with a small amount of low wattage lighting occasionally. Everything else is generally (at this time of year) connected to shore power. When we do take the boat out we have a 24 volt 65 amp alternator to do the honours.

I figured that given our usual type of use, 12 amps ought to be enough to keep the batteries happy.

True, if you never discharge the batteries very much or always arrive back at marina after a fair bit of motoring. In that case they might accept 30A but only for an hour or two and increase in recharge time will not be relevant if you are then on shorepower for the next few days. So fair point.

However, you are then pretty much saying that the batteries will normally be fully charged and so 26.4V seems OK in that case. It will take ages to get to 100% at 24.6V so I see why you asked the original question if worried that they weren't fully charged.

My 12V charger can't be configured properly for my T-105s and I have to fudge things. I can get 14.8V falling to 14.1V for float OR 14.0V falling to 13.3V. I use the former setting for most of the summer at anchor and the latter when in a marina for more than a day. It takes days to reach 100% charge on shore power using the 14V/13.3V (based on temp. corrected SG) as the charger drops to 13.3V too soon.

 

[sarabande]

I am still concerned about the charger's available protocols.

Assuming

1 you have an accurate voltmeter

2 there is no constant drain, only intermittent e.g. water pumps

3 no really deep discharge, say overnight

Then your battery set up really does need some more beef to fill it that last 5 or 10%.


PVB - ooops, I missed the 'flooded' reference, having jumped on the 'paste' reference !

CYGNUSV
Trojan have good support pages.

http://www.atbatt.com/trojan-t-105-6v-deep-cycle-golf-cart-battery.asp

with specific recommendations for various voltages at various states of charge, and I wonder whether you are really achieving a saturated full charge at any stage with a 12A charger.


If the charger profiles do not match the battery profiles, then you cannot achieve full charge, especially if there is substantial extraction of power between or during the charge cycle.

 

[Mistroma]

I am still concerned about the charger's available protocols.

with specific recommendations for various voltages at various states of charge, and I wonder whether you are really achieving a saturated full charge at any stage with a 12A charger.

Trojan say 10% - 13% of capacity initially and 1%-3% in float phase. That would mean 23A charge dropping to 2.3A would be OK. If OP is correct and batteries are usually kept close to full charge then 12A would do the job if configured correctly. However, I'd personally prefer a larger charger than 12A as it wouldn't match my own boat use.

If the charger profiles do not match the battery profiles, then you cannot achieve full charge, especially if there is substantial extraction of power between or during the charge cycle.

I think I was trying to make a similar point. Trojan suggest 29.6V to for quick recharge with 26.4V for float. e.g. If alternator was only putting out 28V the time to charge from 90% - 100% would probably run into days. So batteries might not be as well charged prior to as OP thinks when he returns to shore power. If charger is then going straight to float charge they'll probably never get to 100%. That's one reason I suggested doing an accurate SG to see if it indicated 100% charge. The voltage OP quoted is fine if batteries really are at 100% but we don't know their actual state.

 

[sarabande]

with your comments 100%, Mistroma.

 

[noelex]

I think everything is fine.

Chargers dropping down to a "storage" voltage that is lower than than the float voltage is actually very sensible.
26.4 v is too low for a float voltage, but ideal as a storage voltage.

The only question concerns if the battery charger is recognising discharge from battery and kicking back into a new charge cycle appropriately.

12A @24v is the same power as 24A @ 12v. It sounds like the OPs electrical demands are quite low and this may well be enough to ensure the charger is supplying all the power consumed in which case a storage voltage of 26.4v is appropriate. Even if there are occasional brief discharges it will do little harm.

It is helpful to boost the voltage occasionally to stir up the electrolyte. Some chargers will do this automatically If this not happening turning the charger off and on to force a new cycle say once a week while living on the boat is helpful.