Engine start battery voltage drop. Where to get fixed in Tucson AZ? (solved)

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Engine start battery voltage drop. Where to get fixed in Tucson AZ? (solved)

March 26, 2016, 12:39:35 pm

Hello,

Our Foretravel is new to us. We just bought it from Motorhomes of Texas and left their facility four days ago.

While driving from Van Horn Texas to Benson Arizona, I noticed the voltage had dropped from the usual 13.7 to 11.8. Over the next fifteen minutes it dropped to 11.4. After reading the manual and some info online I decided it was probably safe to turn on the starting "boost" switch and leave it on. The generator was already running (for roof A/C's). The voltage jumped to 11.8 and slowly climbed to 12.1 while driving the last 40 miles to Benson.

Assuming it's safe to drive with the generator and the "boost" switch on, we plan on moving to Tucson today. Is it safe to drive this way?

Does anyone have a recommendation for a reputable/trustworthy shop in the Tucson area?

Also, if someone thinks it might be something easy to diagnose/fix (voltage regulator?), I'm open to suggestions.

Thanks for any help - Joe

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #1 – March 26, 2016, 12:58:59 pm

Joe,

Welcome to the ForeForum.

Yes, it is OK to use the generator to power the inverter/charger to charge the house battery bank and then the boost switch to connect the house bank to the chassis bank.

But, 12.1 VDC is still quite low. Assuming batteries are OK, you should be 13.2-13.5 once the inverter charger "catches up".

What is the amp reading on the inverter/charger remote panel?

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #2 – March 26, 2016, 01:29:56 pm

Hello Brett,

While parking yesterday, I turned off the "boost" switch, generator, and engine. Then hooked up to 50 amp shore power and turned the "boost" switch back on and left it on over night.

Right now, with 50 amp shore power connected and with the "boost" switch either on or off, the inverter/charger remote panel is showing:
AC loads 2 amps
charger 7 amps
total 9 amps
Battery good 13.6 volts

I just put a volt meter on the engine batteries and with the boost switch on or off they show 12.5. I just turned on the ignition and it showed 12.4

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #3 – March 26, 2016, 01:39:12 pm

Joe,

You really should not be loosing ONE FULL VOLT between the house bank and chassis bank. Check connections at both batteries and at boost solenoid. Should be easy to trace down where that kind of loss is taking place.

With a digital voltmeter, place one lead on the house battery positive post (the battery post that has the cable going to the coach). Place the other lead on the cable end itself. If any reading other than 0, that indicates loss of voltage across the connection.

Do the same for each connection: each side of boost switch and chassis battery positive to cable.

Let us know what you find.

It is also possible that some of your batteries are shot. Once fully charged, go to any battery shop and have them load tested (but only when fully charged).

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #4 – March 26, 2016, 01:42:23 pm

Could be an alternator issue, as everyone said you are fine running with the generator and boost sw on. If you are heading you might wait once you are home it may be easier to find a repair shop

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #5 – March 26, 2016, 02:16:57 pm

From what I understand, the boost is only used in cold temps, though we've never needed it even in 20 degree temps. My only question would be, could leaving the boost switch on damage anything else?

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #6 – March 26, 2016, 02:33:45 pm

From the factory, the boost switch connects to a CONSTANT DUTY solenoid.

So, unless someone has replaced it with an intermittent duty solenoid, you are OK using it for more than just starting.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #7 – March 26, 2016, 02:57:32 pm

Quote from: joe g – March 26, 2016, 12:39:35 pm

Hello,

Our Foretravel is new to us. We just bought it from Motorhomes of Texas and left their facility four days ago.

While driving from Van Horn Texas to Benson Arizona, I noticed the voltage had dropped from the usual 13.7 to 11.8. Over the next fifteen minutes it dropped to 11.4. After reading the manual and some info online I decided it was probably safe to turn on the starting "boost" switch and leave it on. The generator was already running (for roof A/C's). The voltage jumped to 11.8 and slowly climbed to 12.1

Assuming it's safe to drive with the generator and the "boost" switch on, we plan on moving to Tucson today. Is it safe to drive this way?

If this is the dash chassis voltage readout, it sounds like the prime suspect would be the alternator. Running with generator and "boost" will keep your engine voltage up so you don't get a check engine light or have other issues with transmission shift pad or engine ECU.

Foretravels use a style of alternator some truck stops aren't familiar with. There should be enough info on the forum to provide a shop with the details of what needs to be done.

Now if instead you're referring to the house batteries dropping from 13.7 to 11.8 with the generator running, this would indicate that the inverter/charger wasn't charging the batteries. You would want to look at the manual for your inverter to see what might be going on.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #8 – March 26, 2016, 03:54:14 pm

Similar symptoms. Alternator belt loose

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #9 – March 26, 2016, 04:54:49 pm

I think I would start by cleaning all battery post connections. Then see if your batteries will charge.
Then check the condition of your batteries.
A bad battery or connection can make all kinds of charging problems pop up.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #10 – March 26, 2016, 05:39:47 pm

Simple test to check alternator: With generator and engine and boost off, turn ignition key on, don't start, note voltmeter reading. Start engine, after running 15 seconds, note voltmeter reading. If alternator is charging you should see a noticeably higher voltage, say 1.5 volts or so. If no increase in voltage, check alternator belt. If alternator belt is ok, alternator is suspect.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #11 – March 26, 2016, 06:23:07 pm

Agree with Peter, it could be an alternator. But a number of other common failure points: Battery isolator, sense wire from isolator to alternator, loose or corroded connection anywhere between alternator, isolator and batteries...

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #12 – March 26, 2016, 06:40:25 pm

Brett, Yes, will be interesting to learn what the outcome is...

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #13 – March 26, 2016, 06:45:56 pm

+1 regarding Brett's suggestion to test for voltage drop from battery post to CABLE.

My starter would not even turn the engine over. I had cleaned posts and clamps. Batteries showed good voltage and tested good on load tests. All connections were physically secure and APPEARED to be good. With a moderate load on the house batteries (ignition switch and a few lights on) there was a significant voltage drop between the clamp and the copper lug a the end of the cable. A bit of scrubbing with a piece of sandpaper on mating surfaces of the lead clamp and the copper lug made a BIG improvement.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #14 – March 26, 2016, 07:22:34 pm

Hello,

Brett, I'll check the house batteries with a volt meter. Thanks for pointing out the voltage difference isn't right.

Michelle, thanks for pointing out that I wasn't clear. It is the chassis batteries that are low voltage and appear to not be getting charged by the alternator/charging system.

I just checked the alternator belt, it's tight. The engine batteries are Optima Yellow Top and appear to all be the same age, but I could only find a date sticker on two of them. Both stickers say 08/13.

Is the battery isolator the component that is in front of the engine and to the right, three terminals on it, blue in color with lots of cooling fins? How to test it?

We drove to Tucson today. After charging the chassis batteries all night via the inverter and boost switch on, the engine started with just it's own batteries, but the voltage after starting didn't go up, but stayed at 12.5. I then started the generator and turned on the boost switch for the drive to Tucson. When we arrived in Tucson, the chassis battery voltage was up to 12.9.

By the way, the rig has about 42,000 miles on it.

Thanks everyone for all the pointers. You've given me plenty of homework

Joe

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #15 – March 26, 2016, 09:44:44 pm

Joe, welcome to the forum. You've bought a great coach supported by fantastic people here. On Monday, I think you will find Motorhomes of Texas to be very helpful as well.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #16 – March 26, 2016, 11:49:33 pm

Joe,

Start as suggested-- checking connections on alternator, isolator (yes it is the "finned thing") and batteries. Pay particular attention to the small "sense wire" to the alternator-- can be from chassis battery or chassis battery terminal of isolator.

And, to test the isolator CAREFULLY, with engine at fast idle (1000- 1100 RPM) check voltage at the center lug of the isolator or at the alternator B+ terminal. Should be around 14.7 VDC. Then check voltage at the outer lugs-- one goes to each battery bank-- they should be around 14 VDC.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #17 – March 27, 2016, 11:36:56 am

I had good experiences at Biguns Truck Service on Valencia Rd. in Tucson.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #18 – March 27, 2016, 07:43:15 pm

I have cleaned all the chassis battery connections and the two terminals that are less than a foot away from the chassis batteries (several other cables are attached to these terminals) and all four connections on the alternator. They were pretty clean already, but the battery terminals were barely snug, not what I would call tight. The alternator connections and isolator connections were all tight. I then started the engine. Before starting, the dash voltmeter showed 12.5 and after starting and idling for about a minute it showed 12.2 and was stable.

With the engine idling at about 1000 rpm, I then checked the isolator. The chassis battery terminal showed a little over 12 volts (not a digital meter. I'd guess it was close to the 12.2 the dash meter was showing). The center terminal showed no voltage. The house battery terminal showed 12.5 (the inverter remote gauge showed 12.7).

Brett, you said the center terminal should show about 14.7, does the no voltage point to the isolator or the alternator?

Thanks - Joe

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #19 – March 27, 2016, 07:54:36 pm

Joe, no voltage on the isolator center post would indicate no alternator output, let's see if Brett agrees...

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #20 – March 27, 2016, 08:30:02 pm

Confirm it by checking at the output lugs on the back of the alternator.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #21 – March 27, 2016, 08:45:29 pm

If you have an alternator problem and are in the Phoenix - Tuscon area, you might want to check with copper state alternator in Phoenix. They told me they also have a shop in Tuscon but I don't know the name. They worked on mine while we were in Quartzsite and apparently did a good repair. They are also familiar with the Duvac system which is a plus. My wife said she sent you a pm earlier, this is just a follow up. Good luck.

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #22 – March 27, 2016, 08:46:08 pm

Broke down while in the Tuscon area last year and I was directed to Premier Motor Coach Services by Carol and Jeff Savournin. I recommend their work as I received excellent service there, call service tech Eric Olstrom 520-624-2024.

Website New & Used RVs for Sale in Tucson Arizona | Motorhomes, Campers, Travel...

Tony

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #23 – March 27, 2016, 09:16:49 pm

Yes, assuming the "sense wire" is connected (it is a small wire and can break) is OK, then indeed, the alternator is the likely culprit if not voltage at B+ of alternator/center lug of isolator (as they are connected by a single large gauge wire).

Re: Engine start battery voltage drop. Where to get fixed in Tucson AZ?

Reply #24 – March 27, 2016, 09:43:01 pm

Joe, just fyi, when you get your failed alternator removed, look it up and verify against your OEM installed alternator amperage spec. Whatever the current alternator is, the shop may just try to match it and replace it without verifying capacity for your coach.

When I bought mine, the OEM alternator capacity was 160 amps, but it had a remanufactured 130 amp alternator installed, which I have since upgraded.

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