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 > Charging both batteries in a Class C from one charger?

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HiTech

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Posted: 12/23/05 07:19am Link  |  Print  |  Notify Moderator

In a Class C motorhome, there is a battery isolator that disconnects the chassis battery from the house battery when parked, but allows them both to charge from the engine alternator when the engine is running. Would one be able to energize this isolator by connecting a battery charger to the chassis battery, thereby charging both the house and chassis batteries?

Jim

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Posted: 12/23/05 07:29am Link  |  Print  |  Notify Moderator

It is possible but not practical. You most likely have a solenoid that couples the batteries. It must be supplied with power. You might consider a very inexpensive small charger to wire in permanently to the chassis battery system. They are less than $50, charge slowly, but who cares . At one amp they will keep it up.
In my boat there is a dual charger for the trolling motor but there was nothing for the engine battery. I put a small multi plug adaptor inside and added a small charger for it. Now when I plug the chargers in they all get refilled.


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HiTech

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Posted: 12/23/05 08:00am Link  |  Print  |  Notify Moderator

Exactly what I do - a charger for each battery. But some in the Class C forum report that when they charge their engine battery, both get topped off. So this is a general question about how isolators in Class C's work. I may even point an item in our FAQ to it.

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itsasecret

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Posted: 12/23/05 08:04am Link  |  Print  |  Notify Moderator

You would need to connect the positive terminal of the charger to the "alt" terminal of the isolater. If you have an isolater, then forget the solenoid, there won't be any, it's one or the other. Your isolater has three terminals, one "in" and two "outs". The "in" is connected to both, but neither "out" is connected to the other. Think two diodes, that's what it really is.


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YoDude9999

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Posted: 12/23/05 08:14am Link  |  Print  |  Notify Moderator

All you really need to do is take a jumper wire and attach it to the two terminals on the isolator that goes to each battery(ies). This connects all batteries together and the coach charger will then charge the chassis battery as well. Do keep in mind, by doing this, if you run your coach batteries dead, your chassis battery will be dead also. The jumper can be made of a 20ga wire 6 inches long with an alligator clip at each end.

If you're not connected to shore power, then you can add a good battery charger somewhere and using the above method, still maintain all the batteries at once.

At the current moment, I have a maintainer type charger keeping up all my batteries, two coach batts and the chassis batt. I am using the jumper as my other charger is doing something else at the moment. Normally I have two chargers running and don't use the jumper wire, but needed a charger for somethng else, so now I'm only running one charger. The jumper wire trick is working well. I see no problems.

As an after thought, I should have mentioned that I only use this method to keep the batteries topped off with a maintainer charger (1.5 amp), not for an actual charging cycle from a discharged state with a high current charger.

* This post was last edited 12/23/05 07:43pm by YoDude9999 *   View edit history


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tcsmith

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Posted: 12/23/05 08:37am Link  |  Print  |  Notify Moderator

One thing to remember also is that a good battery charger "talks" to the battery in a sense. The newer models can even go through desulfur modes, and they run down to a trickle charge when the battery is fully charged so as to not damage it by overcharging.

In a "in series" or "in line" setup, (2 6 volts in series), the batteries look like one 12v to the charger and house, providing 6 full cells (12 volts) of power. But with a house battery + motor battery, they are in Parallel, not series, and they do not appear as one battery. A battery charger could cook one battery while under-charging the other. The cost of one cooked battery will exceed the cost of adding another small 'smart charger' as others have suggested.

* This post was edited 12/23/05 06:23pm by tcsmith *

HiTech

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Posted: 12/23/05 10:53am Link  |  Print  |  Notify Moderator

Great info. So for the Class C owner who believes that when he hooks his charger to just his house battery his engine battery charges, how would this be possible? Here is the thread with the specific example.

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* This post was edited 12/23/05 11:02am by HiTech *

Big Redneck

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Posted: 12/23/05 11:48am Link  |  Print  |  Notify Moderator

My Dodge with the cummins engine has two battery's up front and one battery In the rear now there Is a solenoid going to the rear that Is activated by current produce by the alternator. That the way my Scotty works. The battery minder does not produce enough current to do that.


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Posted: 12/23/05 12:49pm Link  |  Print  |  Notify Moderator

The device that does this is known as a B.I.R.D. Some motorhomes have them, some don't. The bird will energize the isolation relay and parallel both battery banks whenever it sees 13.1 volts or higher and disconnect when the voltage drops below 12.6. Here is the link to the pdf file. http://www.intellitec.com/pdfs/BATTERY_web/5300362.000.pdf

Sam


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HiTech

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Posted: 12/23/05 01:05pm Link  |  Print  |  Notify Moderator

Wow - this looks like a great upgrade to a simple solenoid or isolator relay!

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