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andybarrett1

Battery Charging question

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Hi All

 

Just a quick one as lots of conflicting information out there.

 

Am revisiting my Solar MPPT regulator in the belief the Absorption and Float voltage settings are incorrect, I have maint free lead acids Numax  XV31MF.

 

My question is what should the Absorption and Float Charging voltages be.

 

Absorption Volt Charging   =  14.6v  ??

Float Volt Charging  = 13.5v  ??

 

Thank you for reading

Andy

 

 

Edited by andybarrett1
typo

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I can’t find those batteries with Mr Google but those voltages sound about right for a SLA. 

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4 minutes ago, andybarrett1 said:

Hi All

 

Just a quick one as lots of conflicting information out there.

 

Am revisiting my Solar MPPT regulator in the belief the Absorption and Float voltage settings are incorrect, I have maint free lead acids Lucas  LX105 I think.

 

My question is what should the Absorption and Float Charging voltages be.

 

Absorption Volt Charging   =  14.6v  ??

Float Volt Charging  = 13.5v  ??

 

Thank you for reading

Andy

 

 

You don't want to be at or above gassing levels with sealed batteries as you cannot replace the water / acid.

The gassing voltage depends on temperature and a good battery charger will have a temperature 'probe' and react by changing its output.

I wouldn't suggest going above 14.4v

Battery Temperature Charge Voltage per cell Gassing Voltage for a 12V battery
20 °C 2.43 to 2.53 14.49
25 °C 2.40 to 2.50 14.34
30 °C 2.37 to 2.47 14.19
40 °C 2.31 to 2.41 13.98

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3 minutes ago, WotEver said:

I can’t find those batteries with Mr Google but those voltages sound about right for a SLA. 

Numax  XV31MF :-)

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7 minutes ago, andybarrett1 said:

Numax  XV31MF ?

Hmm... ok. Can’t find a data sheet for them so you could lower the absorption to around 14.4V if you wanted to be super safe but it’s unlikely you’d have any problem at 14.6V. Lead calcium is pretty robust technology but as you’re talking about a solar controller it’s not like you’re time limited so you could follow Alan’s advice if you wish. 

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41 minutes ago, Alan de Enfield said:

You don't want to be at or above gassing levels with sealed batteries as you cannot replace the water / acid.

The gassing voltage depends on temperature and a good battery charger will have a temperature 'probe' and react by changing its output.

I wouldn't suggest going above 14.4v

Battery Temperature Charge Voltage per cell Gassing Voltage for a 12V battery
20 °C 2.43 to 2.53 14.49
25 °C 2.40 to 2.50 14.34
30 °C 2.37 to 2.47 14.19
40 °C 2.31 to 2.41 13.98

 

Are those voltages from the actual battery manufacturer's data sheet or from a general technical document/wed page?

 

They look rather low to me for lead calcium-batteries so may be for lead-antinomy technology.

 

The OPs voltages look like it assumes lead-calcium batteries so the acceptance voltage would need to be set down a bit for lead-antinomy but as Wotever says with solar time is not such an issue with solar so a slightly lower voltage would probably still get the batteries charged unless the controller is being too clever and drops to float too soon.

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1 minute ago, Tony Brooks said:

Are those voltages from the actual battery manufacturer's data sheet or from a general technical document/wed page?

Its from a general specification sheet for charging SLA batteries

 

It suggests 14.6 - 15.1v (at 20*C) for open cells as they can be 'topped up'.

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Just now, Alan de Enfield said:

Its from a general specification sheet for charging SLA batteries

 

It suggests 14.6 - 15.1v (at 20*C) for open cells as they can be 'topped up'.

Thanks Alan, that is what I thought. At least one vendor of AGM batteries is insisting they be charged at (if I remember correctly) 14.7 or 14.8 volts, anyway higher than the i alternator regulator will allow and say their users may need to fit an A to B charger to get the voltage. I am also fairly sure I have se4en 14/.7 or 8 quoted as the gassing voltage for lead-calcium batteries.

 

As it seems the majority of batteries used for inland boat's domestic systems are lead-calcium, sealed or open sell, nowadays the OPs voltages look OK to me unless he has lead-antinomy. Warning - Trojans, Rolls etc may well be lead-antinomy.

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3 hours ago, Tony Brooks said:

... a slightly lower voltage would probably still get the batteries charged unless the controller is being too clever and drops to float too soon.

Definitely something to keep an eye on. If it does, and if there’s no way to change that, then I’d definitely keep the voltage where it is. 

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1 hour ago, WotEver said:

Definitely something to keep an eye on. If it does, and if there’s no way to change that, then I’d definitely keep the voltage where it is. 

I think at least some controllers drop to float on the basis of time in absorption and that may be fine for a holiday boat that spends enough periods tied up with no load because the controller will reset each night. That way over a few days the batteries will be fully charged. I am not so sure it will work for many live aboards whioarguably never managed to get their batteries fully charged by solar.

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1 hour ago, Tony Brooks said:

I think at least some controllers drop to float on the basis of time in absorption and that may be fine for a holiday boat that spends enough periods tied up with no load because the controller will reset each night. That way over a few days the batteries will be fully charged. I am not so sure it will work for many live aboards whioarguably never managed to get their batteries fully charged by solar.

Remember WotEver’s rule about solar:

 

However much you have it will be too much in summer and insufficient in winter. 

 

 

 

... unless your name is Peter...

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Hi all.

 

Thank you for your replies..... It does seem to me that my guess figures seem to be about right :-

 

 

Absorption Volt Charging   =  14.6v 

Float Volt Charging  = 13.5v 

 

All caused from my chasing an alternator fault on a reasonably sunny day   and reading 14.4v on batteries making  someone better versed than me suggest to check the Solar controller..... Just need to work out the panel buttons again now :-)

 

Thank you again

 

Andy

 

 

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8 hours ago, Tony Brooks said:

Thanks Alan, that is what I thought. At least one vendor of AGM batteries is insisting they be charged at (if I remember correctly) 14.7 or 14.8 volts, anyway higher than the i alternator regulator will allow and say their users may need to fit an A to B charger to get the voltage. I am also fairly sure I have se4en 14/.7 or 8 quoted as the gassing voltage for lead-calcium batteries.

 

As it seems the majority of batteries used for inland boat's domestic systems are lead-calcium, sealed or open sell, nowadays the OPs voltages look OK to me unless he has lead-antinomy. Warning - Trojans, Rolls etc may well be lead-antinomy.

 

I agree with this. 

 

The Rolls VRSLA's I used to work with were pure lead plates, rather than lead-calcium,and used to last aboutv30% longer than the lead-calcium ones.

 

I don't think lead-antimony plates have been used on any VRSLA  batteries, only in wet cells, but am happy to be corrected if anyone knows any different.

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I had our Outback 60 MPPT set at 14.8V absorbtion, but found is caused so much gassing that the CO alarms were going off.  This was with Trojan T105s.  A reduction to 14.7 seems to have sorted it out.

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2 hours ago, Boredrider said:

I had our Outback 60 MPPT set at 14.8V absorbtion, but found is caused so much gassing that the CO alarms were going off.  This was with Trojan T105s.  A reduction to 14.7 seems to have sorted it out.

Not surprised because I think they are lead-antinomy. As gassing within reason in such batteries does little harm and maybe good because more lead sulphate is converted by the higher voltage at the ex[ense of more topping up I am sure 14.7 is fine but I would set my regulated voltage on lead-antinomy batteries to around 14.5.

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