alternator to battery charger

Submitted: Friday, May 07, 2010 at 10:28
ThreadID: 78276 Views:3739 Replies:4 FollowUps:6
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has anyone out there heard of a new 30 amp battery charger thats runs off the alternator of the vehicle. Heard a rumour there was new product out. Any info welcome
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Reply By: Member - John and Val - Friday, May 07, 2010 at 11:31

Friday, May 07, 2010 at 11:31
Duane,

Sounds like a 12v to 12v charger, also called a battery to battery charger. There are a few around. Check out this supplier for example. A search on ebay for battery to battery charger will find a lot too.

They take the available voltage (maybe from the alternator) and convert it to the voltage required to charge your battery. Very useful to overcome voltage losses in long cables going from the engine bay to a trailer for example.

Cheers

John
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Follow Up By: Steve and Viv - Friday, May 07, 2010 at 18:40

Friday, May 07, 2010 at 18:40
As longs as said charger is supplied with enough voltage to produce the out put. IE, don't expect much if you put one in your camper then run speaker wire to the back and expect it to do any thing.
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Follow Up By: Member - John and Val - Friday, May 07, 2010 at 19:38

Friday, May 07, 2010 at 19:38
Yes Steve, you are absolutely right. There's been a lot of discussion here recently about the need to use heavy cable. That's a precondition of any successful low voltage system. Thank you for reinforcing that - I shouldn't have overlooked mentioning it.

Cheers

John
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Reply By: Mick O - Friday, May 07, 2010 at 13:23

Friday, May 07, 2010 at 13:23
Duane,

do to the Redarc site and have a look at the BC-DC charger and also the Redarc BMS. Another is the Ranox DC-DC charger.

Ranox DC-DC Charger

Redarc Electricals


Cheers Mick
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Reply By: Member - Scrubby (VIC) - Friday, May 07, 2010 at 17:00

Friday, May 07, 2010 at 17:00
G`day Duane,

I have just recently fitted a 12DC - 12DC 50 amp charger, it is a Starter Battery to Charger model supplying up to 14.8 volts at up to 50 amps.
Other models are available which are Alternator to Charger that do a similar job, however I can use other 12 volt supplies such as solar, constant current old type Battery Charger, 12 volt generator supply, etc. with the Battery to Battery model.
"Stirling" is the make of chargers and are available from " RV POWERSTREAM"

I have no affiliation with this company, just a very satisfied customer.

Regards,

Scrubby.

I don`t know where i`m going but i`m enjoying the journey.

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AnswerID: 415744

Reply By: ChipPunk - Friday, May 07, 2010 at 20:49

Friday, May 07, 2010 at 20:49
The alternator is a battery charger.
It should put out between 13.8V up to 14.4V. (Ideally 14.4V for a discharged battery, dropping to 13.8 once the battery is fully charges - aka its "float voltage".)

If your alternator does not supply the voltage, it is sensing wrong or has a faulty regulator, else is undersized.

If undersized, NO ATTACHMENT will increase its charging capacity.

If otherwise outputting a low voltage, fix the problem or maybe trick it by inserting diodes etc in its Sense line (not possible for single wire D+ alternators).


DC-DC voltage boosters are used to charge one battery from another - ie, it boosts a battery's ~11.5V-12.8V to (say) 14.4V to charge another battery.
It is a fairly inefficient way to charge a battery, but is useful where engine running isn't required or possible...
They are common in cigar-socket battery chargers (used to charge OTHER batteries - not the battery that powers the cig-socket!).

But nothing beats an adequately sized alternator (set to say 14.2-14.4V) for charging batteries.
AnswerID: 415776

Follow Up By: Maîneÿ . . .- Friday, May 07, 2010 at 21:44

Friday, May 07, 2010 at 21:44
ChipPunk has the correct reply because nothing beats an adequately sized alternator for charging batteries.

Because Duane's original question is: "30 amp battery charger that runs off the alternator" and that clearly eliminates all posts about battery to battery devices

Maîneÿ . . .
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Follow Up By: Member - Phil G (SA) - Friday, May 07, 2010 at 23:21

Friday, May 07, 2010 at 23:21
"nothing beats an adequately sized alternator "

Just to clarify your statement, Mainey:
Modern alternators (including those for the 2005 F250) have high capacities - you never find anything less than 80 amps and most are 110 amps or more. A cranking battery will rarely draw more than 30 amps, so size is not the issue.

The issue is voltage regulation. To preserve battery life, most alternators have temperature compensation. This lowers the regulated voltage as the underbonnet temp rises (instead of say 14.2V, the voltage may drop to say 13.5V when hot). This becomes an issue when an auxillary battery (often a wet cell deep cycle) in a cooler environment (say a caravan or trailer) won't get sufficient voltage, even with adequate cables and earth. That is when a DC-DC charger can upsize the voltage to usually 14.4V. But these chargers limit the current to whatever their capacity is.
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Follow Up By: Maîneÿ . . .- Friday, May 07, 2010 at 23:34

Friday, May 07, 2010 at 23:34
Phil,
my statement is: "nothing beats an adequately sized alternator for charging batteries"

The 'voltage regulator' is built into the modern alternator, it's an integral part of the charging system.

Maîneÿ . . .
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Follow Up By: ChipPunk - Friday, May 07, 2010 at 23:54

Friday, May 07, 2010 at 23:54
And we are now talking a different set of requirements.
If temperature compensation is the reason, then surely the converter/charger has a temp sensor. An aux battery in a boot might even be hotter than one in the engine bay....

So, and alternator with temp compensation charges remote batteries UNDER their acceptable charging voltage....
Yep - let's buy a new device. We now see through "current splitting" and smart isolators; multi-electrode splugs and ionic glow-plugs; audio capacitors etc - we need something new.

Or is there data or qualifications to the benefits of this new device.
Let's see - charging at 40A+ at 13.xV versus max 30A at 14.4V... hmmm, I wonder which will charge quickest..?

(I don't mean to mock readers. But lets get to the facts and details quickly.)
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