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Battery being charged or not charged?

January 03, 2012, 02:27:58 pm

I noticed that the voltage gauge on the dash was reading 10 Volts and , having the monitor on, I was getting a steadily dropping reading on the engine voltage reading. After having the alternator checked and getting a reading of around 14V but nothing coming to the battery I thought something was fried in the system. This morning, as an experiment I put the toggle switch on the dash over to the charge position, then started the engine. The dash gage now reads over 12V when idling. Normal?? To the right of the switch is the word "CHARGE" (vertically). to the right of that is the word "BOOST" (vertically).
The toggle switch is a three position switch, with-to the right (boost) is momentarily on. The center position is OFF? Pushing the left side of the switch it then stays in the charge position.

How am I supposed to use the capabilities of this selector switch?? Always left when the engine is running? Only boost position when engine battery needs "help" starting the engine?
Other than that, after having the clutch fail in our toad, and having the air horns not work because a bayonet connector came off under the "hood" we are having a great time.

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Re: Battery being charged or not charged?

Reply #1 – January 03, 2012, 02:37:41 pm

Nitehawk, I have never seen a toggle type switch for the boost switch as you describe.  This sounds like an add on by a former owner.  Sounds like you fixed the problem.  Only thing I would check now is to see that you are not constantly charging the chassis ( engine ) batteries with the boost switch.  NORMALLY chassis batteries are charged with the alternator only, if needed boost switch can be engaged to make starting easier or to charge a depleted or low chassis battery.
Gary B

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Re: Battery being charged or not charged?

Reply #2 – January 03, 2012, 02:59:24 pm

If someone has put a "position 1, off, position 2 switch in the line from the alternator to the batteries, you will blow the diodes in the alternator if it ever feeds "OFF". So I hope this is not what it means.

I would trace the wires from alternator to batteries and just see what someone has done.  It is normal for there to be a battery isolator between the alternator and batteries, though there are several acceptable ways to achieve this (isolation of the two battery banks during discharge, yet both battery banks connected to alternator output while engine running) with the diode-based isolator that Foretravel uses being my least favorite.

Brett

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Re: Battery being charged or not charged?

Reply #3 – January 03, 2012, 03:38:05 pm

let's see if I can describe what we have. In the engine compartment--driver's side, on the frame rail, is an aluminum device with cooling fins. The engine battery cable connects to the first "post" from the front of the coach. The second "post/terminal has the alternator cable. Then, a small gauge wire, Maybe two--I'm not at coach. Then another terminal with heavy electrical cable. I haven't checked where this cable goes. The wiring schematic from Oshkosh Truck does not show this device. There are wires coming from it (I believe) that go into the compartment behind the Driver's side rear wheels. there are two fuses and two black blocks that must have some function but I have no idea what. I tried pulling the two flat fuses and nothing happened.
When I open the engine access door on the driver's side and then look down alongside the engine, outside the frame rail I see a cooling radiator--about 12" square, with a large electrical fan on the top. Function? I don't know but surmise it is a transmission cooler as the tranny gauge very seldom gets up to operating temp range as spelled out in manual.
Guess I need someone that is more versed in electronics than me. If I can't taste it, feel it, see it, or smell it I tend to leave it alone.

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Re: Battery being charged or not charged?

Reply #4 – January 03, 2012, 03:44:23 pm

What Nitehawk is describing is a DIODE-BASED battery isolator.

If that is what you have, let us know and we can tell you how to test it-- very easy with a digital voltmeter.

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Re: Battery being charged or not charged?

Reply #5 – January 03, 2012, 09:52:43 pm

It sounds like the isolator is defective. If the altenator is putting power to the post for the wire from the altenator then the other two large posts should have voltage which will probably be slightly less than the altenator voltage but should be approximatly the same voltage on the two of them. If one has a significant variation the isolator would be bad

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Re: Battery being charged or not charged?

Reply #6 – January 04, 2012, 03:13:54 pm

I had a switch like that on my 1988 Winnebago.  It was built on a John Deere (later to become Oskosh) chassis.  The three positions let you stop charging the house batteries with the engine running (to prevent over-charging), or charge the batteries with the engine running, or (momentary) "boost", connecting the house batteries to the engine charging system and battery to aid in starting.  It used a solenoid type (relay) isolator that was simply engaged or disengaged as needed. 

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Re: Battery being charged or not charged?

Reply #7 – January 04, 2012, 04:28:51 pm

Yes, as Tom said, a solenoid is another way to combine/isolate the batteries.  You likely have EITHER a diode-based isolator (approx 3" X 12" with large metal fins to dissipate heat or a solenoid/relay. IMO better than a diode-based isolator.

Determining what you have is the first step in troubleshooting.

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Re: Battery being charged or not charged?

Reply #8 – January 04, 2012, 09:41:48 pm

your coach has both the diode based isolator and the boost solenoid that had a roicker switch with 3 positions with the center off and one way was boost and the other way allowed the chassis batteries to be charged from the house battery circuit while plugged in

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