Caravan & Camper Battery Charging Feedback

My Pioneer camper has a deep cycle 12v lead acid batt. Camper comes with Arrid 5 stage smart charger. I added 12v maint.free battery in parallel. On standby charging with the charger on 240v, the lead acid is continually being charged and boils. Is this because I've connected 2 different types of batteries? What should I do? Thanks
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Reply By: Member - bungarra (WA) - Monday, Apr 21, 2008 at 21:59

Monday, Apr 21, 2008 at 21:59
There will be others here with a lot of technical knowledge on this and hopefully will respond.....but here is my two bobs worth

my reaction is that the "Arrid Smart charger" doesnt appear to be acting all all that smart!...first check is it faulty?...try charging the batteries separately and see if the problem exists

the multi stage charger that I have.... and there are many other brands ..... all state that dissimilar batteries do not cause a problem when connected in parallel

On the assumption that both batteries are in a healthy state and in a similar state of charge it would seem a little strange

When connecting batteries in parallel I have always made certain that I charge / load by connecting onto the positive terminal of one battery and the negative terminal of the other to ensure the current flow must travel "through" both batteries ( and only recognise the bnk as one) rather than bias one battery if you are connected in parallel but only using the terminals on the one battery for charging / voltage sensing / load....maybe that theory works.....maybe the experts will say not







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AnswerID: 299728

Reply By: Mainey (wa) - Monday, Apr 21, 2008 at 23:40

Monday, Apr 21, 2008 at 23:40
kathy,
in a single word reply ... yes

Said simplistically - when two *different* batteries are connected in parallel they each accept a charge at different rates, this is because the internal electrical resistance of each battery IS different.

The alternator regulator see them as only one battery (because they ARE wired in parallel as one battery) and duly charges them as one battery.
Because one battery is lower resistance than the other it charges at a different rate to the higher resistance battery, this causes one battery to boil in extreme circumstances and/or the other not to fully charge at all !!

Mainey . . .

AnswerID: 299751

Follow Up By: Member - Phil G (SA) - Tuesday, Apr 22, 2008 at 08:47

Tuesday, Apr 22, 2008 at 08:47
Mainey,
#1 Theres no alternator here - its a charger on 240V.
#2 The battery won't boil because theres another one paralleled to it.
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Follow Up By: Mainey (wa) - Tuesday, Apr 22, 2008 at 12:22

Tuesday, Apr 22, 2008 at 12:22
Phil,
Yes I should re post with the terminology '240v battery charger' instead of Alternator "regulator" however the end result is exactly the same, because the two batteries are seen by the battery charger 'regulator' as just one large battery, BUT each battery has different charging and discharging capacities and capabilities and that's why there is the boiling problem, because the two batteries are internally different and do accept charge at different rates, some don't fully charge and some overcharge.

May I suggest your information ""#2 The battery won't boil because there is another one paralleled to it"" is possibly incorrect.
I say this because this thread is about a battery that IS boiling when connected in parallel.

Mainey . . .
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Follow Up By: techo2oz - Tuesday, Apr 22, 2008 at 20:17

Tuesday, Apr 22, 2008 at 20:17
Spot on Mainey,

----------------------T----------------T
| | |
| / /
| \ \
| / R1 / R2
--- V \ \
------- / /
| | |
| | |
-----------------------------------------

This might look rough but hopefully might best demonstrate what you are saying.

Ohms law says that the current flowing through a circuit can be calculated by the formula V/R=I.

Because the same voltage is applied to both branches (or battery in the case in question) if there is a difference in the internal resistance of each battery, then the amount of current flowing through each will be different.


This in part is why it is generally recommended to run similar battery types of similar age in parallel.

Peter
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FollowupID: 566069

Follow Up By: techo2oz - Tuesday, Apr 22, 2008 at 20:19

Tuesday, Apr 22, 2008 at 20:19
Yuck, That looked okay in a preview.
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FollowupID: 566071

Follow Up By: techo2oz - Tuesday, Apr 22, 2008 at 20:30

Tuesday, Apr 22, 2008 at 20:30
Lets try this.



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FollowupID: 566074

Follow Up By: Member - Phil G (SA) - Tuesday, Apr 22, 2008 at 20:54

Tuesday, Apr 22, 2008 at 20:54
Mainey and Peter,

We all know that V=IR and you don't parallel dissimilar batteries. But neither of you have answered the original question: "why is the battery boiling".

A battery will only boil if either:
#1 The charging voltage is excessively high or
#2 A cell is shorted, so the full charging voltage is going to 5 cells instead of 6.

Maybe the charger is stuck on Equalisation, and is delivering 15+Volts??? Need to get a multimeter to find out whats going on.

If Kathy just charged the single deep cycle battery from the charger, I'm sure it would still boil.
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Follow Up By: Nomadic Navara - Wednesday, Apr 23, 2008 at 01:06

Wednesday, Apr 23, 2008 at 01:06
Ohms law does not apply to the current feeding into a battery. We are dealing with an electro chemical action here not a purely resistive circuit. You really should not have two working batteries of different constructions (models/types) connected in parallel.

PeterD
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Follow Up By: Member - Phil G (SA) - Thursday, Apr 24, 2008 at 15:21

Thursday, Apr 24, 2008 at 15:21
Peter,
The way I see it, Ohm's law always applies. The Current that goes into the battery is proportional to the Voltage difference (Charger voltage - battery voltage) and inversely proportional to the Internal Resistance of the battery.

What happens after that is the complicated, mysterious bit.
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Reply By: Member - Phil G (SA) - Tuesday, Apr 22, 2008 at 08:54

Tuesday, Apr 22, 2008 at 08:54
Kathys,
How old is the wet cell deep cycle battery? How well does it work? Will it still run a fridge for a couple of days?

I think your Wet Cell Deep Cycle battery is dead.
Batteries usually only boil if they are getting hit with a high voltage, or one of the cells is shorted.

What voltage does the battery get to when its on the charger and boiling?
AnswerID: 299788

Reply By: kathys - Tuesday, Apr 22, 2008 at 22:39

Tuesday, Apr 22, 2008 at 22:39
Thanks to all for the help. I will get the batteries and the charger checked .
AnswerID: 299974

Follow Up By: Nomadic Navara - Wednesday, Apr 23, 2008 at 01:13

Wednesday, Apr 23, 2008 at 01:13
For a quick check -disconnect the two batteries and charge them individually. When you say the original battery is a "deep cycle 12v lead acid battery" it is a flooded battery (has removable caps on top.) If this is the case you will have to change the battery charger settings to charge each battery as the maintenance free battery requires a lower charging voltage.

PeterD
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