BATTERIES

[dsw]

Do batteries have to be the same amp hour when conecting them together ?

 

[VicS]

Sorry mis read the question

 

[dsw]

yes i know that but what i want to know for sure is would it be ok to connect a 140Ah to a 90Ah ect ect

 

[VicS]

Yes its ok but it may be better if they are not vastly different.

 

[pvb]

[ QUOTE ]
yes i know that but what i want to know for sure is would it be ok to connect a 140Ah to a 90Ah ect ect

[/ QUOTE ]Yes, as long as they're the same basic type, eg wet lead-acid, agm, gel, etc.

 

[sarabande]

Isn't there a problem when one of the pair is charged, and the other one is not fully charged ? Doesn't the charger keep feeding juice at a rate above the "standby" into the already charged one ?

 

[halcyon]

The voltage you see is generated by the battery internal resistance. Thus if you have a low battery and a full battery, the charge will take the least line of resistance, the low battery, so the voltage will not be high enough to charge the high battery. As the low battery increases in charge level and resistance, voltage will rise till the high charge battery will take some charge.

Little somplified, but basic story.

Brian

 

[theforeman]

[ QUOTE ]
.... if you have a low battery and a full battery, ......Brian

[/ QUOTE ]

am i correct in assuming that in the course of normal usage you would only get into that situation if one of the batteries was faulty

 

[halcyon]

You may have a split charge relay system, one battery being the engine, the other the service, or you could have changed a battery.
If you had a faulty battery that was short circuit, you would not get a high voltage, if it was open circuit, the good battery would set the voltage, so would normally be ok.

Normally this is a problem on 24 volt systems, were the charge current has to flow through both batteries as they are in series. Which is why you normally change batteries as sets. You can charge all batteries independantly in a 24 volt set while connected in series, but it gets mind bending.

Brian

 

[sarabande]

It continues to worry me that you have two 12v batteries of different capacity linked in series (?).

Nigel Calder (Boatowners Mechanical and Electrical Manual) counsel against having different batteries linked together (I paraphrase a couple of chapters).

This site
http://batteryuniversity.com/partone-1.htm

seems to give a lot of info, which might throw light on the subject of charging.

Also these sites.
http://www.mpoweruk.com/chargers.htm

http://www.batteryfaq.org/

 

[masterofnone]

I have 2@225ahc on domestic circuit and 1@85ahc cranking battery, the little one wasnt man enough to start the engine so I put a link twixt the banks, forgot to close link when connected to shore power battery charger and boiled the battery in 8 hrs. 3 week old battery, doh.... /forums/images/graemlins/tongue.gif

 

[pvb]

You need to check the settings on your charger. There's no way a charger should "boil" a battery.

 

[William_H]

Your charger should not have boiled the battery unless it was the old crude constant current type. A modern charger with voltage regulation and perhaps staged charging should not boil the battery.
A bit of bubbling is gas escaping. Was it that or real boiling with very high temperature and now totally knackered battery? olewill

 

[VicS]

[ QUOTE ]
It continues to worry me that you have two 12v batteries of different capacity linked in series (?).

[/ QUOTE ] He doesn't. At least he has said nothing to suggest that he has.
Someone else talking about 24 volts etc has confused the issue.

Agree though you would not have two different capacities in series. Several complications if that is done.

Thanks for the link to batteryuniversity Not seen that one before.