Alternator Output is .76 Volts

Topic: Alternator Output is .76 Volts (Read 1986 times) previous topic - next topic

Re: Alternator Output is .76 Volts

Reply #25 – October 24, 2016, 09:17:05 pm

Boost up to 1000 RPM. Read at the chassis battery and also at the house battery. Should be in the low 14's.

Re: Alternator Output is .76 Volts

Reply #26 – October 25, 2016, 12:51:40 am

Brett,

When I use the cruise control to move mine to fast idle, I think it goes to about 1200 rpm. Is that too fast? Is there a simple setting to change it to 1000? What would that do to my slow idle, which I *think* is in the 600-700 rpm range?

Thanks,

Trent

Re: Alternator Output is .76 Volts

Reply #27 – October 25, 2016, 01:18:43 am

I am not Brett, but your VIP Smartwheel cruise controls should work like this in regards to setting the fast idle; Turn the cruise on, tap the "Resume" button, RPM's go directly to 1200RPM. Hold the button instead of tapping it, RPM's rise gradually until you release it and then stay there. If you tap the "Set" button instead of the "Resume" button, RPM's go immediately to 800RPM and stay there until canceled or subsequently raised using the "Resume" button. If the RPM's are higher than that, say from initially tapping the "Resume" button, holding the "Set" button down the causes the RPM's to gradually decline until you release the "Set" button and then the RPM's stay there until you cancel, release the parking brake, apply service brakes, or put it in gear... which of course also applies to any fast idle state that was invoked using the cruise control. Tapping the "Set" button while idling faster than 800 RPM's while drop the RPM's immediately down to 800RPM. Our coach's normal idle is a very stable 700RPM (plus or minus 2 or 3 RPM on the VMSPC)
Don

Quote from: TulsaTrent – October 25, 2016, 12:51:40 am

Brett,

When I use the cruise control to move mine to fast idle, I think it goes to about 1200 rpm. Is that too fast? Is there a simple setting to change it to 1000? What would that do to my slow idle, which I *think* is in the 600-700 rpm range?

Thanks,

Trent

Re: Alternator Output is .76 Volts

Reply #28 – October 25, 2016, 09:13:23 am

Trent,

1200 is fine. My point is that when checking the alternator output, you want the engine RPM above base idle.

Re: Alternator Output is .76 Volts

Reply #29 – October 26, 2016, 02:54:17 pm

I checked voltage at Alternator and at engine batteries. 15 volts at bothe locations. The volt meter on the dash was going back and forth between 14 and 15 volts. It has never done that before.

Re: Alternator Output is .76 Volts

Reply #30 – October 26, 2016, 04:33:50 pm

If you have the OE, diode-based battery isolator, it is not possible to have the same voltage on alternator side of the isolator as on the battery side, as you loose approx. .7 VDC in the isolator itself (turns into heat-- hence all the aluminum fins to dissipate the heat).

If you don't have a diode-based isolator, let us know how yours is wired.

Re: Alternator Output is .76 Volts

Reply #31 – October 26, 2016, 06:09:02 pm

Brett, thanks for your help. I believe the isolator is original. Would I be able to tell by looking at it. With my Primus system its very cluttered and very dirty. I will look at it and try and take a picture.

Re: Alternator Output is .76 Volts

Reply #32 – October 28, 2016, 05:21:56 pm

Brett, here is some info that hopefully helps you, help me. First per Foretravel it is a diode isolator. Here are some readings I took today. First engine battery 13.17 volts engine off. Alternator Pos. 1.02 volts. Neg. 0. exciter 0. Sense wire 13.04. Isolator left conn.11volts. center. 4.9 volts. Above all with engine off. Engine running at 1200rpm battery 14.2-15.3. Alternator pos 13.99-15.4. neg.0 Exciter 3.5 volts Sense conn 14.1-15.3. Isolator center 13.2-15.7. left 14.49-15.11. right 14.89-15.11. Volt meter fluctuates between 14 and 15 volts at idle. At 1500rpm stays at 14 volts. Engine at idle lumbers along with voltage change and so do 12 volt interior lights.

Re: Alternator Output is .76 Volts

Reply #33 – October 28, 2016, 05:58:35 pm

First, that is quite a range of voltage with engine at steady 1200 RPM. Since your "Sense conn 14.1-15.3" reading at the alternator sense terminal is not only wide-ranged, but 15.3 is dangerously high, you could have an alternator/regulator problem. That reading, which is/should be the same as at the chassis battery bank should be in the 14.0- 14.2 VDC range-- yes, a tenth of a volt plus or minus is fine.

And, this will give a reading at the B+ terminal of the alternator and the center lug of the isolator (the large-gauge wire connects them (read same number on each end) of about .7 VDC higher as you loose that amount to heat in the isolator.

But, first, I would verify that connections at alternator, isolator and batteries are clean and tight and than the batteries are in good and not deeply depleted condition, as these can affect readings.

Further, if the isolator is failing, you can bypass it to further identify the problem.

With engine off and chassis battery disconnected for safety, remove at the isolator three wires:
Wire from alternator B+
Wire to the chassis battery
Sense wire

Being very careful to not allow any to touch any metal (ground), use a bolt to connect all three. Now reading at B+, at your jerry-rigged connection and at chassis battery should all be in the 14.0-14.4 range.

Re: Alternator Output is .76 Volts

Reply #34 – October 28, 2016, 06:55:46 pm

Thanks Brett, I will disconnect the engine batterys and clean before reattaching as they are dirty. While disconnected I will disconnect and clean connections at the isolator. Those connections are very dirty and rusty. As stated earlier The connections are hard to get to. And I will very careful not to short across any ground. Maybe the connections are adding resistance to cause voltage to be high. I cant thank you enough for your help.

Re: Alternator Output is .76 Volts

Reply #35 – October 28, 2016, 06:58:29 pm

I forgot to mention I will try the bolt method to see if voltage will come down.

Re: Alternator Output is .76 Volts

Reply #36 – October 29, 2016, 02:23:05 am

Quote from: joeszeidel – October 28, 2016, 06:55:46 pm

And I will very careful not to short across any ground.

The only safe way is to make sure you are not connected to a shore line AND disconnect BOTH battery banks from the RV.

Trent

Re: Alternator Output is .76 Volts

Reply #37 – November 03, 2016, 05:59:26 pm

Well here is an update on my progress. First I disconnected both the house and engine batteries. I then crawled under the coach to access the isolator. I removed wires one lug at a time cleaned them with electric parts cleaner and steel wool. Then applied dielectric grease and reattached and tightened. I found several to be somewhat loose. I then restarted and found the voltage still fluctuating. I have three optima red top batteries that would charge but I didn't know how old there where . I removed all three batteries and called optima to fine two batteries eight years old and one was nine years old. I took them to the local car quest and had them load tested. I have two failed batteries. I will pick up three new batteries Saturday and install . I am hoping this solves my problem. Brett and those on this thread thanks for your suggestions. I may be slow but I don't give up.

Re: Alternator Output is .76 Volts

Reply #38 – November 05, 2016, 11:45:32 am

Well my problem still exists, I installed three optima red tops this morning. I measured 12.3 with engine off. When I started the engine my voltage is still high at the battery 14.8 at 1200 rpm. Also inside the coach a clicking sound was comming from the dash behind the dash air box. When I turned on the fan the clicking stopped. Dash lights appear bright and flicker. My next step is to remove the alternator and take it back to where I had it rebuilt. I believe the problem maybe the votage regulator. Any thoughts?

Re: Alternator Output is .76 Volts

Reply #39 – November 05, 2016, 12:06:01 pm

Before doing anything else, fully charge those new batteries. 12.3 is close to 50% discharged.

If on shore power, hit boost switch so that the inverter/charger will charge the house bank and the boost solenoid (yes, assuming it is working) will charge the chassis battery bank. VERIFY with voltmeter.

You should also see the amp rate of charge go way up when the boost switch is turned on.

Only after everything is back to "the way it should be" would I do any more!

Re: Alternator Output is .76 Volts

Reply #40 – November 05, 2016, 01:18:30 pm

Ok I have left the coach with a battery tender on. It should charge at a slow rate. I will check tomorrow afternoon.

Re: Alternator Output is .76 Volts

Reply #41 – November 05, 2016, 02:01:27 pm

How many amps does the battery tender put out?

How many amp-hrs in the chassis battery bank?

I.E. "can you get there from here".

The advantage of the inverter/charger with boost switch is that it will start in bulk mode and as as voltage rises/amps decrease will automatically drop voltage.

Most battery tenders do not have the needed to bring up large battery banks discharged to 50% capacity. They are great (and designed to) MAINTAIN only.

Re: Alternator Output is .76 Volts

Reply #42 – November 05, 2016, 02:17:12 pm

Its a 2 amp. I do have a larger charger I can put on with auto shutoff.

Re: Alternator Output is .76 Volts

Reply #43 – November 05, 2016, 02:36:30 pm

Good, because a 2 amp charger and several hundred amp-hr battery bank 50% discharged won't get you there!

Re: Alternator Output is .76 Volts

Reply #44 – November 05, 2016, 02:51:28 pm

Brett, I took my 10 amp charger and replaced the battery tender. This charger will reduce amps as batterys charge and then go to a trickle mode. Thanks again.

Re: Alternator Output is .76 Volts

Reply #45 – November 06, 2016, 10:47:52 am

Well Brett, here the latest reading take this morning after the new batteries got a full charge. Engine off, engine batteries 12.69 volts. House batteries 13.70 volts. Engine running at 1300 rpm, engine batteries 14.52-15.02, house batteries 15.22-15.27. Alternator 7.90-15.23. Very strange.

Re: Alternator Output is .76 Volts

Reply #46 – November 06, 2016, 12:03:31 pm

Yes, sounds like an issue with the voltage regulator and/or alternator.

Re: Alternator Output is .76 Volts

Reply #47 – November 06, 2016, 12:10:54 pm

Thanks Brett, next step is remove and return to rebuild shop.

Re: Alternator Output is .76 Volts

Reply #48 – November 07, 2016, 06:39:18 pm

Well first let me say Thank you Brett for staying with me on this issue. Now I took the alternator back to the rebuild shop and bench tested it. An of course its perfect. Upon reinstalling I discovered in my earlier haste to install, I installed the excite and sense wires in reverse. Pretty dumb huh. Now that its installed correctly, the voltages are as follows at 1200rpm Engine batteries 14.04v. House batteries 14.24v and Alternator 14.98v. No fluctuation . All is well I have clean terminals at the isolator, new engine batteries and a rebuilt alternator. I can only that shop rates around me are $145/hr. I don't mind spending money on items but labor money can saved by listening to the help offered on this forum. Many thanks again.

Re: Alternator Output is .76 Volts

Reply #49 – November 07, 2016, 07:11:58 pm

Glad you got the wiring sorted out.

Affiliate Notice