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Charging 12v from 24v with Trace C60?


By dave123, Section Homebrewed Electricity
Posted on Mon Feb 14, 2005 at 10:32:19 PM MST
can this be done?

I am looking for a way to charge a camper battery bank (12v) from a truck's 24v system while driving.  Would using a higher amperage charge controller work for this?  The 24v alternator is rated at 60 amps, and I was thinking of using four golf cart batteries in series/parallel for the 12v camper section.

I don't ever plan on running the batteries too low, preferrably no more than 20% discharge (80% remaining).
Charging 12v from 24v with Trace C60? | 13 comments (13 topical)

Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#1)
by TomW on Mon Feb 14, 2005 at 03:57:19 PM MST

Dave;

Just a teaser now but Don and some of us over on IRC are working on a device that can use any voltage from 3 volts to 12 volts and charge any battery bank voltage up to 120 VDC. Just in the testing stages now so watch this space for the announcement on a release date. Kits will be offered and possibly completed units at reasonable cost.

Just one of the many projects we are working on soon to be offered on redevices.com. The website is registered but not up yet so don't go looking just now.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it




Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#5)
by RobC on Mon Feb 14, 2005 at 08:12:21 PM MST

Tom this is something I have been hoping to see for a long time. I think its a great idea.RobC

[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#2)
by BT Humble on Mon Feb 14, 2005 at 04:47:03 PM MST


I am looking for a way to charge a camper battery bank (12v) from a truck's 24v system while driving.  Would using a higher amperage charge controller work for this?  The 24v alternator is rated at 60 amps, and I was thinking of using four golf cart batteries in series/parallel for the 12v camper section.
I don't ever plan on running the batteries too low, preferrably no more than 20% discharge (80% remaining).

I use a couple of light bulbs in series as a current limiting device to charge my various small batteries (power tools, camera, flashlights, 12V 7Ah gel batteries, etc.) from my 24V bank.  I'm usually only putting 300-800mA into a battery, but the same technique would work perfectly well if you're prepared to monitor the state-of-charge of your 12V bank.

Should cost under $5 for the bulbs and wire, too.

BTH



Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#3)
by RobC on Mon Feb 14, 2005 at 06:43:10 PM MST

I used heating elements from a junk electric furnace to limit 45 volts into 12 volt batterys to no more than 25 amps charge. Its waste power but works okay.RobC  

[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#4)
by RobC on Mon Feb 14, 2005 at 06:56:13 PM MST

I forgot to mention you also need to salvage some of the ceramic insulators to hold the wire as it can  easily get red hot and start a fire! I use 5 pieces in long enough lenghts that I get the amps and not concentrated heat. Problem is this high powered resistor doesn't know when the 12volt batterys are fully charged thats up to you.

[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#7)
by BT Humble on Mon Feb 14, 2005 at 10:18:49 PM MST


I forgot to mention you also need to salvage some of the ceramic insulators to hold the wire as it can  easily get red hot and start a fire! I use 5 pieces in long enough lenghts that I get the amps and not concentrated heat. Problem is this high powered resistor doesn't know when the 12volt batterys are fully charged thats up to you.  

That's why I use light bulbs, and limit the current to about 5A (ie. 60W 12V car headlight).  It's slower, but if I forget to switch it off for an extra hour or two there's little chance of doing any harm.  I also try to charge at the C/10 rate.

BTH

[ Parent ]



Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#11)
by ghurd on Tue Feb 15, 2005 at 07:09:03 AM MST

BTH,
Have you looked at the PB137ACV?  
A TO-220 chip and a 35 ohm resistor make a charge controller, and you might not need the resistor.  About a US$.  Automatic 13.7v float.
G-
Ghurd.info
[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#12)
by BT Humble on Tue Feb 15, 2005 at 02:10:09 PM MST


BTH,
Have you looked at the PB137ACV?  
A TO-220 chip and a 35 ohm resistor make a charge controller, and you might not need the resistor.  About a US$.  Automatic 13.7v float.

Sounds pretty nifty, but I have to charge everything from AA nicads to 12V deep cycles.  I have a piece of wood with 6 "festoon" globes arranged in series on it, and a short jumper lead with an alligator clip to select the resistance I need.

I guess it's one of those "It ain't broke, so why fix it?" things for me. ;-)

BTH

[ Parent ]



Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#6)
by dave123 on Mon Feb 14, 2005 at 08:41:00 PM MST

The multi-voltage controller sounds interesting.  Would it have its own current limiting ability?

I guess the main question is, what will the amp flow be when a charge controller initially connects the two battery sources?  More than the 60 amp rating of the controller?  I am not sure.  It seems that when you hook batteries in parallel of the same voltage, there is be an immediate but very short amp spike, and then they level out.  Then again, if I used a resistance to control amperage, the charge controller cannot perform its 3 stage charging, which is what I want to occur, without babysitting it (I will be driving the truck).



Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#8)
by ibedonc on Mon Feb 14, 2005 at 11:12:42 PM MST

yes, it has current limiting / fold back . more to come , Tom has to do some testing


[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#9)
by Kevin L on Tue Feb 15, 2005 at 05:36:22 AM MST

You could try to charge two 12V batteries in series, then pull Load A @12 V off of one battery and Load B @12 V off of the other.  The loads would have to be isolated.  Someone else better confirm that this drawing is acceptable.  


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Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#10)
by Kevin L on Tue Feb 15, 2005 at 05:40:55 AM MST

On second thought use a fuse on 1 and 3 as well.  No since taking any risks.

[ Parent ]


Re: Charging 12v from 24v with Trace C60? (3.00 / 0) (#13)
by alcul8r on Wed Feb 16, 2005 at 08:32:54 AM MST

Not a good idea to charge together but discharge with different loads.  Will overcharge one if it does not get as much use as the other.
alcul8r KansasWind.com
[ Parent ]


Charging 12v from 24v with Trace C60? | 13 comments (13 topical)
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