Caravan Battery Charging

On this site I have noted several methods of charging batteries in a caravan from the vehicles alternator. Some with a simple relay, some with a Redarc relay and some with and Arrid Twin charger.
I am using a simple 80 amp relay with 16mm cable (4 swg) to charge my batteries which works OK and never had a problem starting my engine in the mornings after running off the caravan batteries all night.
Why should I pay big bickies for an Arrid Twin charger or even a Redcar relay? I notice in Derek Beser's diagrams that there is no mention of an Arrid twin charger although he does mention a Redcar relay.
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Reply By: Robin Miller - Sunday, Jan 11, 2009 at 08:52

Sunday, Jan 11, 2009 at 08:52
No real reason Ray, espically if you keep an eye on your batteries.
We do this and it helps to have a permanent voltmeter attached.

The Arrid and equivalent systems can simply be faster and more efficent as they supply a more correct voltage and they also reduce the need for the heavy cables.

The arrid is more set and forget.



Robin Miller

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Follow Up By: RV Powerstream P/L - Monday, Jan 12, 2009 at 08:29

Monday, Jan 12, 2009 at 08:29
Robin
I would think that your statement is 100% correct in relation to the supply amps and if 20A is all that is available then a 20A smart charger is more efficient and faster than 20A normal as it compensates voltage.

The other points of consideration is battery type for acceptance of charge and Battery Temperature compensation.

It would be an interesting experiment with high recombination batteries to run an efficiently cabled normal 50A charge against a 20A Smart Charge.
Ian
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Reply By: Member - Phil G (SA) - Sunday, Jan 11, 2009 at 12:10

Sunday, Jan 11, 2009 at 12:10
The Arrid is a neat bit of gear, boostly the charging voltage to up to 14.4, but I won't use one in my canopy because:
#1 Charging current would be limited to 20amps.
#2 My alternator puts out good voltage - usually between 14.0 and 14.2.
#3 I use thick wire, good connectors and fusible links to minimise volt drop. I measure voltage continuously at the terminals of the 3rd battery, so I know whats going on.
#4 I don't use wet cell deep cycle batteries.

I've tested my batteries after the drive home, and they take no further charge with a CTEK charger, so my alternator is doing fine with the 2 cranking and 1 AGM batteries I use.
Like you, I keep it simple.
AnswerID: 343705

Follow Up By: Member - Ian F (WA) - Sunday, Jan 11, 2009 at 13:56

Sunday, Jan 11, 2009 at 13:56
Phil,
What type of cranking batteries do you use?
Ian
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Follow Up By: RV Powerstream P/L - Sunday, Jan 11, 2009 at 17:57

Sunday, Jan 11, 2009 at 17:57
Phil
You are spot on .
Unless a smart charger can utilise the available spare capacity of an alternator it is an unwanted cost.
20Amps normally does not use whats available unless the alternator continuos duty is only 20A then the smart charger will be worth while due to the boosted voltage.
If you have a 100A alternator it could have 50A spare why strangle it back to 20A and have to pay for the pleasure of choking it.
Ian
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Follow Up By: Member - Phil G (SA) - Sunday, Jan 11, 2009 at 19:21

Sunday, Jan 11, 2009 at 19:21
Ian F,
I currently have a pair of Exide Extreme N70. Previously I have used Yuasa/Century Overlander. Both are conventional wet cell batteries. I don't like "sealed" and I don't like "Calcium"!

Ian RV,
Yep. Interestingly, Redarc have come out with a product that upsizes the voltage (just like the Arrid), but only gives you 5 amps. What good is that?
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Follow Up By: RV Powerstream P/L - Monday, Jan 12, 2009 at 08:16

Monday, Jan 12, 2009 at 08:16
All units that produces less than what the alternator can spare will choke the system.

The average alternator of around 80A is cold rated and has a continuous duty of 60% is just under 50A less what the car need s to run so why waste it with a so called undersized smart charger.

Ian


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Follow Up By: Robin Miller - Monday, Jan 12, 2009 at 08:46

Monday, Jan 12, 2009 at 08:46
An interesting aside to the step up voltage type chargers would be to look at a battery that charges better at a lower voltage.

I currently run an orbital battery which surprisingly to me, spends a lot of time below 12v and hence really sucks the current out of an alternator.

Haven't investigated it properly just yet but as I am looking at getting a new main battery (I only use 1 permanent battery)
I would look carefully at specs on terminal voltage at full charge and internal resistance.

I.E. if the average potential of battery type A is 1/4 volt lower than battery type B , then battery type B should charge better and have quicker recovery.

Robin Miller

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Follow Up By: Member - Matt M (ACT) - Monday, Jan 12, 2009 at 09:12

Monday, Jan 12, 2009 at 09:12
Ian,

Not sure I agree with your assertion that, "All units that produces less than what the alternator can spare will choke the system." This assumes that the batteries are able to accept the spare capacity from the alternator without boosting the charging voltage to overcome internal battery resistance and hence increase the charge that the battery actually accepts.

Correct me if I am wrong, but a 'spare' 50 amp charge from the alternator does not mean that the battery is accepting a 50 amp charge. Surely this is governed by the battery type and the voltage differential?

Cheers,

Matt.
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Follow Up By: RV Powerstream P/L - Monday, Jan 12, 2009 at 11:55

Monday, Jan 12, 2009 at 11:55
Matt
Go back up to Robins first post andcheck my answer as believe I reflect the same considerations.
Battery Acceptance .Correct Cabling
Temerature Compensation.

Maineys point is also a good one as the cabling from any charge source to the Caravan regardless of smart or not is critical to what voltage gets to it.

Locating a small smart charger at the front of a vehicle with the battery being charged at 6M away unless the smart charger has the capacity to compensate for voltage drop from undersized cable then no way will 14.4V get to it.

Some smart chargers are designedto compensate up to 1.5V drop but I find it better not to mention that as it is agreen light to reduce cable size and still stuffthe system.

That has already happened with the zero volt drop splitter where onechap said you beaut I can use smaller cables .

For the littlle bit extra copper and cost oversize do not undersize as prematurely failed batteries far outweight the cost of correct cabling to start with.
Ian
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Reply By: Maîneÿ (wa) - Monday, Jan 12, 2009 at 08:39

Monday, Jan 12, 2009 at 08:39
Ray,
of course you would "never had a problem starting my engine in the mornings after running off the caravan batteries all night" simply because the Cranking battery is isolated from the caravan battery by your 'simple relay' so it does remain fully charged :-)

I would be more interested in your Voltage @ the Caravan battery, not the Cranking battery, does it get charged above 14.4 Volts with the 16mm cable ?

Mainey . . .

AnswerID: 343817

Follow Up By: RV Powerstream P/L - Monday, Jan 12, 2009 at 12:15

Monday, Jan 12, 2009 at 12:15
Assuming a 6M run to the van at 20A and the cable is 16MM2.

16mm2 or 4GGE B&S voltdrop 0.204
6GGE " " 0.325
8GGE " " 0.517
10 " " " 0.822

Deduct that from the capacity of the charger be it smart or just plain alternator.

Ian

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