generators draining batteries

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gamerbus

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Sep 23, 2006
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Virginia Beach, VA
I have an RV that was formerly used as a classroom. It is equip with two 6500w onan generators. The first generator powers two AC units and the second powers the interior walls including a Magnetek series 900 converter/charger.
The problem I'm having is that when I run the generators, the batteries, all three of them, two house and one chassis, go dead fairly quickly. I had them both running today for about three hours and the batteries were drained. There was nothing running on the 12v system during this time.
Anybody know where I should start to look? This can't be normal since the generators are supposed to charge the batteries, not kill them. Is the charger just to small?
Thanks for any ideas.  Greg

 

King

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Jan 30, 2006
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Normally, the magnatek is only connected to the house batteries, and while the vehicle engine should charge the house batteries as well as the chassis battery, nothing in the house system should discharge the chassis battery.  The magnatek does not have the capacity to charge up a partially discharged battery bank in any reasonable amount of time.  The maximum charging current is probably less than 10A, and would take days to charge them.  If you are not connected to shore power, just starting the generators would probably discharge the house batteries more than the magnatek can charge them in a day.  I would recommend when running the generators, plug in a conventional charger to bump up the batteries, or get a new converter with a healthy charging rate.  Others in this forum can direct you to a good alternative converter, but they are expensive.
Art
 

Karl

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A few answers may help point us in the right direction.
Which of the Magnatek 900 series converters is it?
What type and how old are the batteries?
Are all three batteries connected in parallel (assuming they're all 12V), or is it a combination of 12V chassis and 2-6V house batteries? Something else? Describe how they are hooked together as best you can.
How do you charge them now if all three go dead? Shore power? Engine?
If you disconnect the positive battery cable from the batteries, what is the resistance reading between the positive battery cable (not the battery positive post) and ground? Make sure shore power is off and generators are not running when doing this test.

There willl probably be more questions depending on your answers to these.
 

gamerbus

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Sep 23, 2006
Posts
7
Location
Virginia Beach, VA
I'm finding lots of interesting things while poking around with the voltmeter.
First, the Magnetek is a series 900, model 940 and it is only putting out 11.6 v.
It also appears that the coach disconnect relay is not working and is stuck in the disconnected position. I have to say that I'm not sure that the coach batteries have ever had a charge on them since I've had them. They are not charging with the alternator or the Magnetec.
The coach batteries are 12v in series, both deep cycle.

The chassis battery charged  right up with the engine and it does fire the generators right up. I'm guessing the generator ignition is draining the chassis battery and the charger is not working well enough to compensate. Does this sound reasonable?

Do I need coach batteries for anything? I don't have a traditional RV interior and don't run an inverter. I would like to have them available for the 12v lights for when the generators are not running, but that's about all.

Don't be afraid of offending me if I don't make sense. My knowledge of testing electrical stuff mostly involves pushing the power button on.
 

John From Detroit

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Apr 12, 2005
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26,472
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Davison Michigan
Re: the converter's output.. Problem with measuring it is that the batteries, if you have a shorted cell, will drag it down big time.

However I suspect you know how to test that,  also unfiltered DC may read lower than filtered.  If you know what a hardening condenser is (used with high power audio amps right at the amp's input to smooth out power for those super loud bass notes that rattle the windows 3 blocks away) you might try temporarly replaceing the batteries with one of those... Then turn on one 12vdc light and measure voltage.  Should give you an honest reading.

If it's true the Magtech is anemic... Try an Progressive Dynamics Intella Charger WITH charge wizard as a replacement.  If you have flooded wet cells in that rig this is with out a doubt the best converter I've found in my research.
 

King

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Jan 30, 2006
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MA
The first thing to do is fix the disconnect.  It most likely disconnects the magnatek from the house batteries.  The Magnatek needs to be connected to the house batteries to provide a stable regulated output.  The output actually drops down if the load is disconnected.  Also, There should be some method for the engine alternator to charge the house batteries, either a relay, or a diode isolator.  On my unit, the house batteries start the generator; if they can't do it, I can start the engine and the generator will start right up. Also do you have access to shore power?
Art
 

gamerbus

Member
Joined
Sep 23, 2006
Posts
7
Location
Virginia Beach, VA
Thanks for the help guys.
I believe this whole system has been neglected and there are probably several items to address. First I'll replace that disconnect to at least get the house batteries back in the loop. Seems like a good first step.  I do think that charger is week also and now that I read about the newer staged chargers that monitor the system, I want one.

King, yes, i have shore power available.
 

Gary RV_Wizard

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Feb 2, 2005
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West Palm Beach, FL
The Magnetek 940 is a decent (but not wonderful) 40 Amp converter/charger. That means it can put out at max of 40 amps at about 13.5 DC volts. Priority for the converter output goes to any electrical load (e.g. 12V lighting) and the balance is available for battery charging.

I'm skeptical of the 11.6V output measurement, unless it is with the charger line connected to a shorted battery,  which will drag the voltage down big time.  I've never heard of a charger that failed in such a way that it still worked but at low voltage. It's theoretically possible for a charger to fail in that manner, but very unlkely so I suspect either bad batteries or a faulty measurement.

You said "The coach batteries are 12v in series, both deep cycle".but that doesn't make sense.  Or maybe that is reason you are geting a strange voltage reading form the charger.  12V batteries should be wired in parallel, not series. Only 6V batteries are in series.  If the batteries each have 6 cells (count the water caps), they are 12V; if only 3 cells they are 6V.  Series wiring means the positive terminal on one battery connects to the negative terminal on another. In parallel wiring, its positive to positive and negative to negative.
 

gamerbus

Member
Joined
Sep 23, 2006
Posts
7
Location
Virginia Beach, VA
Gary, I wish you were my neighbor.
The two 12v deep cycles are hooked in parallel. The chassis battery tested bad and I replaced it. I replaced the disconnect switch and now get over 13v out of the charger. It's all recharging now. I'll keep an eye on it to make sure it's all good now.
Thanks again to all.
 

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