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Topic: Low voltage from alternator? (Read 1029 times) previous topic - next topic

Re: Low voltage from alternator?

Reply #25 –
Quote from: red tractor –
There is a small wire hooked to the output terminal. Maybe that is the sense wire. With the engine not running there should be no voltage on the output stud on the alternator. If there is remove the small wire and see if it has voltage on it.

That is the ground side. That is another wire using the ground connection at the alt.

Re: Low voltage from alternator?

Reply #26 –
Quote from: prfleming –
When I got my '91 U300 home and checked it over, with engine running I had low voltage at the battery (~12.5V) and really low voltage at the dash (~11.5V) - similar problem - traced it to 2 issues:

The PO had replaced the alternator with a reman LN 130 amp without a sense terminal, just enough so the coach was drivable to sell it.

This is for sure the original alt. There is a date on it somewhere I saw. 1994.

I installed a new alternator with higher amperage and sense capability. This fixed the battery voltage.

Still getting a 1 volt drop at the dash.

Turns out that voltage drop was across the 25 year old ignition solenoid under the dash board. Replaced that and fixed the 1 volt drop at the dash.

I might have to look into this. I am not seeing a voltage drop from batteries to dash gauge though I think. It's hard to say exactly what the voltage is when it is analog but I really think it's closer to 12.5 at the dash not 13 like I stated earlier.

Re: Low voltage from alternator?

Reply #27 –
Quote from: AC7880 –
Start by cleaning all terminals on alternator, solonoids, isolator, batteries.  Some look like they need it.

After the pics I poste did clean all the connections at the ALT and ground lugs. I still need to do the isolator but I am seeing the same voltage at the alt as the input lug of the isolator. In addition I am seeing equal voltage at all the output bank lugs.

Re: Low voltage from alternator?

Reply #28 –
Quote from: wolfe10 –
Indeed, generator powering inverter/charger will charge the house bank.  Through boost switch, that charges the chassis battery.

A "work around" for alternator-based charging that can take you cross country.

This is exactly what we did to make it 4 hours away from home. It worked but even with the boost on I never saw over 13v at the dash gauge. I really need some additional digital gauges installed asap!

Re: Low voltage from alternator?

Reply #29 –
Well a quick update after our trip home. I drove with the genset running, boost switch on, and never saw more than 12.? volts. Somewhere between 12 and 13 on the analog gauge. I will have to dig into it further in the next week or so.

Re: Low voltage from alternator?

Reply #30 –
It just occurred to me- with no voltage improvement with genset and boost, you may have a bad boost relay. First, make sure it "clicks" when you flip the boost switch on and off. Next test with a digital volt meter at the battery posts - or read both sides of the boost relay directly.

With engine off, genset off and no shore power, put some load on the chassis battery, headlights on, heater fan on high. What you want is to make the chassis battery read different (lower) than the house batteries. Now flip the boost switch, if the relay is working the 2 voltages should now be exactly the same, if the voltages remain different you have a bad boost relay (in addition to other possible problems).
 
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B
 

Re: Low voltage from alternator?

Reply #31 –
I was reading some of my old posts and realized I committed the worst forum sin! I never posted the follow up to solving the Alt issue!! Arg, I would be so mad at myself if I had read through all this only to see no solution.

In the end I installed a 28Si delco remy style alt. I also installed a Victron isolator and wired it for sense and excite. All voltages good, charging works great. No more issues.