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Old 07-25-2015, 02:34 PM   #1
Join Date: Apr 2015
Posts: 18
Year: 1993
Chassis: Vista
Engine: Dt360
Alternator questions!

Hey yall I've got a couple questions I could use help with. I've got a Thomas international Vista 93

Soo I've noticed lately that my dash volt meter has been reading low at 12v with no load and drops way low to 10 when I run my lights. I'm under the idea that that means my alternator is weak and that is a reading of my batteries depleting voltage. Soooo I took my multimeter and did some prodding to find that ,engine off, my batteries are at 12.7 which is low. And engine running, my front battery is around 13.4 while the other one stays low at 12.5. When I kill the engine they reach an equilibrium of 12.7. What I've learned is that my alternator is not churning out enough voltage to charge them back from starting, is that the right track? The batteries are less than a year old, I got new cables and terminals already. I haven't checked the alternator at is posts because I can't really get to it.

I killed a starter in the past and I'm thinking this is the root cause. I've replaced the starter, the solenoid, gotten new batteries and changed the terminals only to now notice my new batteries being drained.

Does this seem like an alternator issue? Any other way I can troubleshoot the problem? Whats a proper voltage range to both batteries that my alternator should be throwing out while running my engine?

Thanks guys any information helps! I'm always trying to learn more about what I need to know.

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Old 07-25-2015, 05:06 PM   #2
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Join Date: May 2010
Location: Montana
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Year: 1995
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I would check and double check your grounds before anything else. If that checks out, I say alternator. eBay or Amazon is a good place to find one.
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Old 07-25-2015, 05:16 PM   #3
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Location: Andrews,Indiana
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Year: 1991
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Engine: 3116 Cat 250hp
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Disconnect the batteries and check individually, sounds like you may have a bad one.
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Old 07-26-2015, 03:37 PM   #4
Join Date: Apr 2015
Posts: 18
Year: 1993
Chassis: Vista
Engine: Dt360
So today I started it up, before I did I checked both batteries and they were at 12.8/7

After starting the front one was at 13.3 with the bus idleing and the other was still at 12.8/7.

I disconnected them from each other and charged them both up off the alternator, which was putting out about 13.4.

If I turned the headlights on it would go down to 13 and if I put the fan on too it would drop to 12.8.

After charging them both up individually I connected them together again and they both read 13.3 while running the engine.

After killing the engine and checking after a little time passed they both read 12.9

Sooo what conclusions can I come too?

What's an acceptable voltage range from my alternator on both batteries while it's running?

Is 13.3 too low of a number, maybe a weak alternator? It seems even running just headlights it can't cover the voltage.

Thanks yall!!!
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Old 07-26-2015, 05:29 PM   #5
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Join Date: May 2010
Location: Farmington Hills, Mi (Detroit area)
Posts: 1,340
Year: 2000
Coachwork: Eldorado Aerotech 24'
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12.7 volts is a fully charged battery. With the engine running you should see 13.5 to 14.5 volts at the battery terminals. After the engine has been shut off the batteries should read 13 to 13.5 volts - this is called a surface charge and will bleed off over a few hours down to 12.7 or so. Over a few weeks a normal battery will slowly drain down to 12.5 volts or so.

The true test of battery charge is done with a hydrometer. if one cell reads low that battery needs to be replaced.

Most auto parts stores will test your batteries and alternator for free.

How your batteries are cabled makes a difference too. Proper cabling for a two battery bank looks like this:

Having the positive cable on one battery and the negative (ground) on the other gives both batteries the same current flow so they charge equally. Having both the positive and negative cables on one battery will under charge the second battery.

From here it looks like your system is working though possibly the alternator is a bit weak.
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Old 07-26-2015, 05:51 PM   #6
Join Date: Apr 2015
Posts: 18
Year: 1993
Chassis: Vista
Engine: Dt360
Thank you my batteries are run just like the picture and your info helps me feel like its all good.

My starter will stick randomly and I noticed the low battery voltage and thought it might be the alternator but it seems okay. Ive replaced the terminals, starter, batteries and solenoid and thought maybe it was the alternator that killed my last batteries and starter and is now making the new batteries low thats making my starter stick.

Now im just gonna check everything for a short or weird ground and replace the toggle switch I dunno.

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Old 07-26-2015, 07:06 PM   #7
Bus Nut
Join Date: Dec 2014
Location: Florida
Posts: 584
Year: 1988
Coachwork: Blue Bird
Chassis: I.H.
Engine: DT360
Toggle switch? Is that a battery cut off switch?
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Old 07-26-2015, 08:51 PM   #8
Join Date: Apr 2015
Posts: 18
Year: 1993
Chassis: Vista
Engine: Dt360
No its a toggle for the starter. I turn my key and the engine wait lightcomea on when it goes off I push down the toggle switch that throws the starter. It was added by the prior owner, I was told there used to be a different switch. It connects between the solenoid and the batteries I think and it could be set up funky.
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Old 07-26-2015, 10:57 PM   #9
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Posts: 4,075
Remember that you have a mechanical engine. Once you start your bus, the only juice you'll need is for lights and radio. You don't have a half dozen computers needing power.
I'm hungry!

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Old 11-12-2015, 11:21 AM   #10
Join Date: Apr 2015
Posts: 18
Year: 1993
Chassis: Vista
Engine: Dt360
Sooo it's been some time and in that time I've replaced my alternator, because it finally went caput. It throws out a good voltage.

Now I'm having issues with my starter. The same issues I was having a year ago. Last year I'd throw my starter switch after the wait light goes off and it would not spin and would blow the fuse from the solenoid. Since then I've replaced my batteries, terminals and starter, which mostly solved the problem, thou sometimes It would still have a delay from when I engage the switch to when the starter would spin. I then replaced the solenoid and didn't have to much of an issue for a bit.

Now I'm having the same issue again. I'll turn the key, wait for the light to go off and throw the starter switch and ,just sometimes, nothing will happen until the fuse blows. Usually when I replace the fuse it will work fine after. At this point I've replaced the starter, solenoid, batteries, terminals and my alternator, nd while the issue did mello out it now has the same problem it once had.

Could it be a short in the wires? Maybe this new solenoid is funky already? I'd be a bit annoyed if this new starter got damaged already. I'm gonna poke around and check it all out but any advice would really help.

Thanks yall!!
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