Volts issue

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Volts issue

October 13, 2017, 10:56:36 am

Yesterday I was going to MOT to have a couple of things checked out, it is a 2.5 hr drive from my house. About 2 miles from MOT a check engine light came on, I had them check it and they said it was low voltage probably alt going out. Aubrey also checked the boost solenoid it was bad too. they changed both and checked the new alt and showing 14.2 volts so I was on my way home at 5:15. 5 miles down the road the check engine light came back on and I looked at the gauge and it was showing less than 13 volts. MOT was closed so I switched on the boost and the volts came up and the light cleared and I drove it home.. MOT had told me that this was a was to get home if your alt failed, i'm glad Aubrey checked and changed the solenoid. and I made it home. now the question it why are the volts low with the new alt??? is there something I can check or replace

Re: Volts issue

Reply #1 – October 13, 2017, 11:08:03 am

Could easily be a failure of the battery isolator. Easy to verify. With engine running and at about 1000 RPM check at the following locations on the diode-based isloator:

Center lug of isolator/B+ terminal of alternator= high 14's.
Each outer lug (one to each battery)= approx .7 VDC less than center lug and around 14 VDC

Could also be a poor connection at either battery bank or at isolator.

Let us know the readings and we can direct from there.

Re: Volts issue

Reply #2 – October 13, 2017, 11:42:20 am

Quote from: hdff – October 13, 2017, 10:56:36 am

MOT was closed so I switched on the boost and the volts came up and the light cleared and I drove it home...

You did good activating the boost switch - that was the correct response to your situation. You didn't say if you also cranked up your generator. If not, remember, any time you are in the situation you described, you should also have your generator running. This will provide good stable voltage to the engine and transmission ECU, and it will simultaneously recharge your depleted engine start batteries. We have had some members drive thousands of miles in this configuration, when they suffered alternator or isolator failure on the road.

Re: Volts issue

Reply #3 – October 13, 2017, 12:55:58 pm

Quote from: wolfe10 – October 13, 2017, 11:08:03 am

Could easily be a failure of the battery isolator. Easy to verify. With engine running and at about 1000 RPM check at the following locations on the diode-based isloator:

Center lug of isolator/B+ terminal of alternator= high 14's.
Each outer lug (one to each battery)= approx .7 VDC less than center lug and around 14 VDC

Could also be a poor connection at either battery bank or at isolator.

Let us know the readings and we can direct from there.

wow sorry to say I am not familiar with any of that so I will have to do a little research to find what you are talking about..... I did check the red box by the boost solenoid in the front of the motor compartment that Aubrey at mot checked yesterday. at normal idle it was reading 12.3 at both of the large posts......... with out the boost. could somebody direct me as to where the Center lug of isolator/B+ terminal of alternator and each outer lug are located? Wolfe lunch is on me if you are in the Pasadena area (or I can come to league city) and want to get some hands on teaching.......
also in checking today I noticed that all 3 of my engine batteries , optima red tops, are dated from 2010, could a battery going bad contribute to this issue???

Quote from: Chuck & Jeannie – October 13, 2017, 11:42:20 am

You did good activating the boost switch - that was the correct response to your situation. You didn't say if you also cranked up your generator. If not, remember, any time you are in the situation you described, you should also have your generator running. This will provide good stable voltage to the engine and transmission ECU, and it will simultaneously recharge your depleted engine start batteries. We have had some members drive thousands of miles in this configuration, when they suffered alternator or isolator failure on the road.

woops, sorry forgot to mention that the ginny was running because here in Texas we are still running the a/c, heat index here today is mid 90's!!!

Re: Volts issue

Reply #4 – October 13, 2017, 03:43:03 pm

Quote from: hdff – October 13, 2017, 12:55:58 pm

...could somebody direct me as to where the Center lug of isolator/B+ terminal of alternator and each outer lug are located?

No need to apologize - we ALL had to learn this RV terminology one way or another.

What you are looking for is the battery isolator. It may be the "red box by the boost solenoid" that you mentioned, or that might be something else. The isolator will have some big heavy (probably red) battery cables attached to several posts along with other smaller wires, and may have some "cooling fins". See the photo below as a example of what to look for. Your isolator may have only 3 big posts, or it may have more than three. The ones you are interested in are the large posts marked in the photo.

The "Center Lug of Isolator" is where the alternator output cable connects. When the engine is running, the voltage on the isolator center post should read the same as the voltage on the large POS (B+) output terminal on the alternator.

The large "Outer Lug" on the left is connected to one of your two battery banks.

The large "Outer Lug" on the right is connected to the other battery bank.

If you have additional smaller connection posts on your isolator, disregard them for the purpose of this discussion.

NOTE: SHOCK HAZARD Use caution when working around the alternator or the isolator! There is high DC voltage present!

What Brett would like you to do is (with engine running at about 1000 rpm) first: check the voltage on the center lug.

Then, check the voltage on both the left and the right "outer lugs" (battery post #1 and #2 in the photo).

When you report back here with those numbers, then we can tell you if your isolator is functioning properly, and go from there.

Re: Volts issue

Reply #5 – October 13, 2017, 09:06:36 pm

Thanks I'll check it in the morning and report back.....
could the battery age play a factor also?

Re: Volts issue

Reply #6 – October 13, 2017, 09:09:30 pm

Sure. A battery with dead cell or even really poor connection will not give "normal" readings. This shows up more in rapid discharge than in poor charge voltage, but that can happen as well.

If in doubt about the batteries, FULLY CHARGE and drive to any parts house that can load test them (usually free).

Re: Volts issue

Reply #7 – October 13, 2017, 09:40:26 pm

Stupid question #2 of this thread.... if I have to take the batteries out is there a proper way to disconnect/reconnect the 3 batteries? I've never had anything with more than 1 battery. Also I have optima red tops now, is that a good choice for this application? They all have date stickers of 2010..

Re: Volts issue

Reply #8 – October 13, 2017, 09:42:09 pm

Disconnect negative/ground FIRST. Connect negative/ground LAST.

Optimas are fine for chassis/start batteries. Would not consider them for coach batteries.

Re: Volts issue

Reply #9 – October 13, 2017, 09:57:22 pm

Thanks Brett

Re: Volts issue

Reply #10 – October 14, 2017, 02:30:33 pm

Ok I went out and checked
The lug on the passenger side 14.3
Center lug. 15.4
The lug on the drivers side. 14.2

This was at 1000 rpm,s

Here are some pics of what I have, looks like it's been there a while

Re: Volts issue

Reply #11 – October 14, 2017, 02:38:30 pm

All those readings are just fine.

So, next time you get low voltage readings while driving, stop and check at these same places.

Also, make sure all connections are clean and tight, particularly at the battery end.

Re: Volts issue

Reply #12 – October 14, 2017, 03:42:22 pm

Ok thanks, it did it again today when I was taking it back to the storage, so apparently it is not going to be hard to duplicate. I will go over some time this week and let it idle and see if it will come on at storage and take the connections loose and clean them somehow .. today the volt meter was low before I put the boost on to silence the alarm

Re: Volts issue

Reply #13 – October 14, 2017, 03:53:04 pm

If connections at alternator, isolator and batteries are clean and tight, pay particular attention to readings at isolator. A failing diode or one that is loose that is "making and breaking) can cause this.

Re: Volts issue

Reply #14 – October 14, 2017, 06:36:42 pm

Quote from: wolfe10 – October 14, 2017, 03:53:04 pm

If connections at alternator, isolator and batteries are clean and tight, pay particular attention to readings at isolator. A failing diode or one that is loose that is "making and breaking) can cause this.

so if it ends up being a failing diode that would be the isolator going bad?

I started working nites tonite so it might be Tuesday or Wednesday before i'll be able to update

Re: Volts issue

Reply #15 – October 14, 2017, 07:23:47 pm

Yes,

If, for example you get the same high 14's reading on the isolator center lug, but more than 1 volt less at one of the outer lugs, the isolator is bad.

Replace it with one with at least the same amp rating OR one of the other alternatives (marine ON-OFF switch) or solenoid-based isolator.

Re: Volts issue

Reply #16 – October 14, 2017, 07:45:24 pm

Quote from: wolfe10 – October 14, 2017, 07:23:47 pm

Yes,

If, for example you get the same high 14's reading on the isolator center lug, but more than 1 volt less at one of the outer lugs, the isolator is bad.

Replace it with one with at least the same amp rating OR one of the other alternatives (marine ON-OFF switch) or solenoid-based isolator.

since I don't know much about them I would probably go back with what I have.. may tap you for your suggestion if I get to that point.
thanks

Re: Volts issue

Reply #17 – October 16, 2017, 08:16:37 pm

I am in the same boat...

Now that all 3 8D batteries are replaced.. I've got an alternator putting out 14+ and an isolator with rusted posts showing nothing.

From what I've been told, I could replace the isolator with a switch... that I would have to remember to flip. But it would keep the house and start battery up. (Doug has explained it to me, but I still haven't understood the whole swap.) Like hdff my inclination it just to replace the part.. but i realize with 1992 technology, there's gotta be room for improvement in some places.

My hot water is working again! Sweet. I had a $400 shower before the thermostat went bad. Now 4 parts to get the hot h2o.

Re: Volts issue

Reply #18 – October 16, 2017, 10:26:38 pm

Quote from: Paully – October 16, 2017, 08:16:37 pm

I am in the same boat...

Now that all 3 8D batteries are replaced.. I've got an alternator putting out 14+ and an isolator with rusted posts showing nothing.

From what I've been told, I could replace the isolator with a switch... that I would have to remember to flip. But it would keep the house and start battery up. (Doug has explained it to me, but I still haven't understood the whole swap.) Like hdff my inclination it just to replace the part.. but i realize with 1992 technology, there's gotta be room for improvement in some places.

My hot water is working again! Sweet. I had a $400 shower before the thermostat went bad. Now 4 parts to get the hot h2o.

from what I understand an isolator is pretty basic and probably pretty much the same, they still make one like mine... there is a pic of a new one similar to mine in post #4 that is cheaper

Re: Volts issue

Reply #19 – October 22, 2017, 09:53:10 pm

Ok I have had a chance to go to the coach twice and check the volts. Both times the dash guage was showing 14 volts, that is normal.....also an update, now that I'm lookin at the guage with my cheaters on, previously the guage was going below 12 not 13 when the alarm was going off... so I'll just have to keep trying it and see if it will duplicate.....

Re: Volts issue

Reply #20 – October 23, 2017, 08:21:38 am

14 volts at chassis and house batteries is fine with engine running and/or with inverter/charger IN BULK MODE.

That is too high for FLOAT voltage on inverter/charger unless ambient temperatures are at or below freezing. You need to check your inverter/charger programming in that case.

Re: Volts issue

Reply #21 – October 23, 2017, 10:25:24 am

The ~14v was on the Gauge on the dash with the engine running, boost button off and ginny off plugged in to shore power. The dash gauge was the one at ~12 when the check engine light/buzzer were going off

Re: Volts issue

Reply #22 – January 02, 2018, 02:38:09 pm

Finally a follow up. The regulator on the new alternator was bad and erratic. Had the alternator changed out under warranty and a new isolator installed. All seems to be ok now.. thanks for all of the advice here..

keith

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