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Old 07-07-2008, 11:45 AM   #1
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House Battery Charging System

I have often lamented about how an alternator is not well suited for dealing with the rigors of properly charging a house battery. I have tried little tricks to make it better but never was satisfied. What I really wanted is a sophisticated 3-stage charger tending to the needs of my house battery when parked AND when traveling down the road. Here is my latest attempt at being nice to my batteries.

I have used a relay to act as a transfer switch so that my three-stage charger gets power from either shore power (plugged in) or from an Inverter. The inverter gets its power from the Alternator when the engine is running. When I plug into shore power, the relay automatically connects AC power to the charger. When there is no shore power, the charger "looks" for power from the inverter, which turns on when the alternator begins to produce voltage. It is REALLY simple and seems to work well. The two main components are the inverter and the relay. I have had it out several times since installation and it works great.

One additional benefit is that I can use another set of contacts on the relay to also trickle charge the engine starting battery when the van is parked and just plugged in. That way, if the van is going to sit for a while, all batteries are "fresh" when I am ready to use it. When I unplug AC shore power, the batteries separate.

I need to clean up my documentation anyway and will send a copy to anyone who is interested in the details.

One of these days I will install solar and make this even less of an issue.

Mike Wilson
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Old 07-08-2008, 11:42 AM   #2
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Are these modifications to the SMB versions of the electrical, or something you built yourself?
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Old 07-08-2008, 12:10 PM   #3
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I guess it is a little of both. My van came with diode isolator so my modifications consisted of the following:
Remove the charging wire from Isolator to the house battery
Unplugging the charger from the AC Socket and plugging it into my relay box. Plugging my relay box into the AC Socket (that used to have the charger plug.
Installing an Inverter in the engine area to pick up power.
Running 120 volts from inverter to the the relay box in the back and bringing charge voltage back up to the starter battery (attached at the isolator).

So all the original Sportsmobile stuff is still there, but some of it is disconnected.

Does that help? If not, I can send you a diagram which contains more details.
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Old 07-08-2008, 09:44 PM   #4
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Very interesting

Dealing with a dead AGM pushed me to think in exactly the same direction. I would greatly appreciate a diagram when you have time. John
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Old 07-09-2008, 09:07 AM   #5
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Yes. Please post the schematic when you got time.

Joe
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Old 07-09-2008, 04:01 PM   #6
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Mike I had a long discussion with the guys at SMBW about a similar issue. I installed a 200 amp alternator and my monitor shows that the house batteries (2-210 AH AGM’s) are always being hit with about 4 to 5 amps @13.8vDC. Being the solar tops the batteries to 14.2 I don’t have a under charging problem but I have been concerned about the alternator pushing too much at them for long drives. I am looking for a (smart) regulator to control the amount of charge out of the alternator. Is there such a device? I would rather not run the inverter every time I start up and if I install any kind of switch more than likely I would forget to turn it on or off when needed. I have the newer separator but would like to see what you did. BTW SMB said they don’t think the batteries can be harmed by the constant charge put to the batteries while driving. In the past I was told this shortens the life of a battery but those were wet cells not AGM’s.
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Old 07-09-2008, 05:47 PM   #7
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Dave you should call AGM and ask them that. They're very helpful and knowledgeable about their batteries.
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Old 07-09-2008, 05:52 PM   #8
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When I replaced my last AGM battery in September, I was told that the problem was overcharging...the dealer/installer pointed out that the battery sides were bowed out, indicating an overcharging situation...
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Old 07-09-2008, 09:16 PM   #9
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For many years SMB used Lifeline AGM batteries. Bob was the contact person at Lifeline ( http://www.lifelinebatteries.com/contact.php ), and he was always very helpful. While there have been concerns about overcharging for years, Bob indicated that he had not seen their batteries damaged by overcharging, but rather by undercharging. This makes sense because the starting battery(s) are subject to the same voltage from the alternator that the house battery(s) are. This is also why SMB recommends solar panels and/or connecting to shore power to fully charge the house battery(s), as the alternator will only charge the house battery(s) to about 90% capacity.

Lifeline's original case design was replaced several years ago with a stronger one to eliminate the case "bulging" that was visible to a certain degree on a new battery.

SMB started using East Penn Deka AGM batteries last year because of the nationwide warranty service available, and for the fact that they enabled SMB to hold prices on the batteries (lead prices were skyrocketing).

I hope this helps.

John K.
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Old 07-09-2008, 10:16 PM   #10
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Daveb,
I too was looking for a smart charger and I don't think the alternator does that. I feel that the best I could do was what I did. By the way, the Inverter that I am using is way less than $100 and the relay is about $30 with shipping etc. The whole thing was less than $100 bucks.
Although possible, I would not try to use an existing inverter.
Also, there are no switches to be left in the wrong position. I have done that so I made this fully automatic. Well... mostly.

Also regarding over vs undercharging.
My experience was undercharging using the van only for recreation. But daily drivers will complain of over charging. I think this system deals with both of these scenarios well.

I think there are systems that package the concept I have implemented but I don't know any without some research.

Mike
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