Low voltage from alternator?

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Low voltage from alternator?

July 01, 2021, 11:06:31 am

Hello all. Went to fill up the fuel tank last night and noticed the volt meter was reading low. I spent many hours last night and this morning researching and searching this forum for answers. I found a lot of really good info. Here is where I am at.

I have the Powerline 25-15 190A alt
4 post battery isolator (2 of the outputs are wired together (coach bat bank) for redundancy on the diodes as I understand)

I have 13.6v out of the Alt to the isolator.
I have 12.6v out of the isolator to chassis and coach battery bank, voltages match

I don't appear to have a sense wire. Is one of the posts on the back of my alt a sense terminal that I could add a sense wire? I just have an exciter wire hooked up and that matches the wiring diagram for my coach.

That voltage seems low to me. The dash gauge is showing battery voltage or alt output voltage? If it is supposed to show alt output the gauge is not accurate. If it is showing the chassis battery voltage it appears to be correct.

It seems my isolator is working properly. Could I have a bad regulator on the alt? Needs adjusting? Or is it possible that I need to add a sense wire?

ps. I see the cut wires on the isolator that appeared to be a Trik L charger thingy was removed. It matches the color of wires I have seen on other pics. It also looks like it was wired wrong anyways.

See pics and let me know what you think. Thanks!

Re: Low voltage from alternator?

Reply #1 – July 01, 2021, 11:12:16 am

Okay one more question I forgot to ask. In these pics is this yellow wire the sense terminal perhaps? It looks like it is wired to another terminal on the alt, perhaps to the voltage regulator and it is self sensing somehow?

Re: Low voltage from alternator?

Reply #2 – July 01, 2021, 12:27:11 pm

Quote from: nbluesky – July 01, 2021, 11:06:31 am

1. I have the Powerline 25-15 190A alt.

2. I don't appear to have a sense wire. I just have an exciter wire hooked up and that matches the wiring diagram for my coach.

3. That voltage seems low to me. The dash gauge is showing battery voltage or alt output voltage?

4. It seems my isolator is working properly. Could I have a bad regulator on the alt? Needs adjusting? Or is it possible that I need to add a sense wire?

5. I see the cut wires on the isolator that appeared to be a Trik L charger thingy was removed. It matches the color of wires I have seen on other pics. It also looks like it was wired wrong anyways.

6. The yellow wire?

Here is what I think FWIW:

1. That Powerline 25-15 is a strange model number. I can't find it listed anywhere. I would like to see the original Hehr wiring diagram, but no luck so far?

2. I believe you do have a sense wire. I think your factory wiring diagram is mislabeled. The wire B59 RD goes from the alternator to a 15 amp circuit breaker on your isolator panel. That circuit breaker (assuming it is not tripped) is connected to a post on the AUX start solenoid. That post is connected to the START battery post on the isolator. Therefore, wire B59 RD is HOT all the time and should be reading START battery voltage. It is a SENSE wire - not a EXCITE wire. An EXCITE wire is only hot when ignition switch is ON. The diagram for my coach was also mislabled in exactly the same way.

3. I agree - the charging voltage is low. Should be more like 14.5 volts at the isolator alternator post, and about 13.8 at the (three) isolator battery posts. Your dash gauge should read START battery voltage (minus line loss in the wire from the batteries to the gauge).

4. If I am correct in my answer to #2, then you do not need a SENSE wire. It is possible the voltage regulator is not functioning properly, Or it is possible it is not reading the start battery voltage correctly. I think you would be better off having the SENSE wire connected directly to the start battery post on the isolator or even MORE better directly to the POS post on a start battery.

5. You are correct - if those wires were for a Trik-L-Start then they were hooked up incorrectly. Should have been on the START battery post and (one of the) COACH battery posts.

6. I can't see the yellow wire good enough to comment. I need to see the official wiring diagram for your exact model alternator to know what wires should be connected where.

Re: Low voltage from alternator?

Reply #3 – July 01, 2021, 12:43:44 pm

Seeing you have decent output from alternator, I'd think I would go straight to this;

Amazon.com: Victron Energy Argo FET Battery Isolators 200-2AC (2 Batteries...

jk

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Re: Low voltage from alternator?

Reply #4 – July 01, 2021, 12:50:40 pm

Quote from: kimosabe99 – July 01, 2021, 12:43:44 pm

Seeing you have decent output from alternator, I'd think I would go straight to this;

Amazon.com: Victron Energy Argo FET Battery Isolators 200-2AC (2 Batteries...

jk

Not a bad choice if he does need to replace the diode-based isolator and wants to stay with an isolator rather than a going to a combiner.

But, his "fix" may be as simple as having a correctly wired sense terminal (from any location on the chassis battery side of the battery isolator). Lots less $$.

No question, if the sense terminal is tied to the alternator B+, it will NOT work correctly as the voltage drop across the diode-based battery isolator reduces charge voltage too far.

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Re: Low voltage from alternator?

Reply #5 – July 01, 2021, 02:00:26 pm

I believe you need more than 14v at the alternator to get enough volts to give you comfort to the batteries because, as described above, there will be some loss at the isolator and wiring runs.

Some of the regulators have an adjustment and some have been replaced by regulators without that option. As I recall a very small adjustment goes a long way.

Having a proper sensor wire is obviously important.

Re: Low voltage from alternator?

Reply #6 – July 01, 2021, 02:06:57 pm

Yup, alternator needs to "what voltage you want at the chassis battery (will be the same at house, but sense wire is always chassis battery) PLUS loss across the diode-based isolator.

So, if you want, say 13.8 VDC at the chassis battery PLUS .7 VDC loss across the diode-based isolator, alternator output must be around 14.5 VDC.

Go to some other form of battery isolation that doesn't have the voltage loss, and sense wire becomes unnecessary (can be tied to B+, for example) or use an alternator that does not have an external sense terminal.

Re: Low voltage from alternator?

Reply #7 – July 01, 2021, 02:54:36 pm

Quote from: wolfe10 – July 01, 2021, 02:06:57 pm

Go to some other form of battery isolation that doesn't have the voltage loss, and sense wire becomes unnecessary (can be tied to B+, for example) or use an alternator that does not have an external sense terminal.

I respectively disagree. Even without isolator loss you have voltage loss in the wiring from alternator to the batteries. Under high current conditions (charging batteries or running headlights, heater fans, etc.) a sense wire allows the alternator to maintain voltage at the batteries under various loads and will reduce time to charge the batteries. Sense wire can be connected to the alternator B+, but this defeats the original purpose of having a sense wire.

Re: Low voltage from alternator?

Reply #8 – July 01, 2021, 03:16:40 pm

Peter,

Yes, in a coach with undersized wire from B+ to battery I AGREE.

But in the Foretravel you have a very short run from alternator to the "connections at the front of the engine room. With either a manual switch or non-voltage dropping battery isolator and the short run of large gauge wire, I would be very surprised if there is a .2 VDC drop even at high amp charge rates and virtually nothing at lower charge rates.

Absolutely no question, with either long wire runs of smaller gauge wire OR a "voltage dropping" battery isolator, the sense wire and terminal are CRITICAL.

Pretty easy to test though-- if no voltage drop in isolator, remove sense wire from sense terminal and temporarily connect to the B+ terminal. Measure voltage from B+ to ground and voltage at the chassis battery.

But, if you have an alternator with sense terminal (OE) if is either an advantage or at worse a neutral even if going to a low voltage drop battery isolator option and absolutely critical if staying with a diode-based battery isolator.

In our sailboat with high amp alternator and smart regulator and factory wire undersized for the high amp alternator, and almost always charging batteries discharged to 50% (on anchor), I did choose to run a sense wire RATHER than upgrading at considerably more $$$ and hassle to run wire sized to carry the higher amp load. Gave up a little efficiency for lower cost and less hassle of pulling 15' of large-gauge wire.

Re: Low voltage from alternator?

Reply #9 – July 01, 2021, 03:26:13 pm

Lots to read and digest. Stopped for lunch on the road and gauge is reading a steady 13v. Using generator and boost just to make sure I keep everything charged. Running ac too so might as well

Re: Low voltage from alternator?

Reply #10 – July 01, 2021, 03:37:15 pm

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.

Re: Low voltage from alternator?

Reply #11 – July 01, 2021, 03:42:31 pm

1Volt drop from alt to battery could easily be dirty ground connections or a single weak battery cell. IMHO. The wires dont rewire them selves in the dark ( Lucas only) . So, if it has been working as it is , then look for the things that deteriorate over time. Grounds, battery, etc.
I have found many instances of adding a ground cable directly to increase the operating voltage. Just like the Ford headlight switch loss that leads to dim headlights. Adding a relay and shortening the headlight cable while reducing the switch loss does wonders for the headlights' lumens.

Re: Low voltage from alternator?

Reply #12 – July 01, 2021, 06:08:41 pm

Quote from: Protech Racing – July 01, 2021, 03:42:31 pm

1 Volt drop from alt to battery could easily be dirty ground connections or a single weak battery cell.

The thing is, Noah reports he is only seeing "13.6v out of the Alt to the isolator". Even if he wasn't losing ANY voltage between the alternator and the start battery bank, he would still have a problem.

13.6 volts will never fully charge his depleted start batteries. It might be enough to maintain fully charged batteries, however.

Noah reported (above) while on the road with generator running and boost switch engaged that dash volt meter only shows 13 volts. That is another suspicious data point IMO. If the generator is running, and the battery charger is turned on, and the boost switch on turned on, then I would expect to see above 14 volts on the dash volt meter. Something ain't right.

Re: Low voltage from alternator?

Reply #13 – July 01, 2021, 06:32:37 pm

Quote from: Chuck & Jeannie – July 01, 2021, 06:08:41 pm

Noah reported (above) while on the road with generator running and boost switch engaged that dash volt meter only shows 13 volts. That is another suspicious data point IMO. If the generator is running, and the battery charger is turned on, and the boost switch on turned on, then I would expect to see above 14 volts on the dash volt meter. Something ain't right.

Absolutely true as long as inverter/charger is in BULK or ABSORPTION mode. Float mode will (and should be) lower.

Re: Low voltage from alternator?

Reply #14 – July 01, 2021, 06:53:38 pm

Quote from: wolfe10 – July 01, 2021, 06:32:37 pm

Absolutely true as long as inverter/charger is in BULK or ABSORPTION mode. Float mode will (and should be) lower.

Agreed. I believe my Magnum MS2812 holds the batteries at 13.1 VDC (float) in the AGM profile setting.

Edit: No, I was wrong. Looked it up. Float voltage for (East Penn) AGM2 profile is 13.5 VDC. See chart below:

Re: Low voltage from alternator?

Reply #15 – July 01, 2021, 07:20:04 pm

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.

Re: Low voltage from alternator?

Reply #16 – July 02, 2021, 09:03:54 am

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.

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.

Re: Low voltage from alternator?

Reply #17 – July 02, 2021, 09:31:35 am

Start by cleaning all terminals on alternator, solonoids, isolator, batteries. Some look like they need it.

Re: Low voltage from alternator?

Reply #18 – July 02, 2021, 09:34:08 am

I know this subject is sometimes difficult for those not familiar with RV electrical systems to understand, but let me see if I can clarify:

It is desirable to have totally separate batteries for HOUSE and CHASSIS. That way, if you run down the house batteries, you can still start the engine.

So, you have to have some system to separate the battery banks, yet allow both banks to charge from the alternator. Yes, desirable to also have both banks charged from a 120 VAC source (shore power or generator) but that is NOT standard on many coaches/coach brands.

Foretravel chose, as did many other manufactures to use a DIODE-BASED battery isolator. Inherent in its design is around a 7/10 volt loss (turned into heat, hence the fins to dissipate the heat). Because of this drop in voltage DUVAC alternators are used. They have sense terminal/wire that tells the alternator what voltage is on the battery side of the isolator. So, the alternator then puts out 7/10 of a volt higher so that the correct voltage is achieved at the battery.

There are several other choices that achieve the battery separation while discharging but allow both banks to be charged. In the case of this different "device" with no voltage loss, a DUVAC with sense wire is no longer critical.

So, what are these other "devices"?

Simplest is a manual ON-OFF switch, Alternator B+ and chassis battery to one terminal, house battery to the other. Switch off, alternator charges the chassis battery. ON, both banks are charged. And, when ON both banks are charged by alternator OR 120 VAC. Also, when ON, makes a heck of a battery boost option. VERY KISS, but does require owner input. Being a big KISS theory guy this is how our Foretravel was wired for the 150,000+ miles we had it.

There are more expensive zero volt drop isolators.

There are battery combiners-- probably the best modern "automatic" alternative.

Because there are several good ways to address the root issue, there are a number of good solutions. Kind of like Chevy vs Ford discussions, most have their favorite, but as long as the basic "separate to discharge/combined to charge" requirements are met, you are good to go.

Re: Low voltage from alternator?

Reply #19 – July 02, 2021, 10:56:37 am

I'm sorry I have been busy but I will make a proper response soon. We made it to camp with no issues, voltage does seem low to me even with the boost switch on. I will be doing more research today. I did clean all the alt and ground terminals after these pics. Still need to do the iso terms.

Thanks for everyone's input, I'll post more later today.

Re: Low voltage from alternator?

Reply #20 – July 02, 2021, 11:38:59 am

Quote from: wolfe10 – July 02, 2021, 09:34:08 am

Also, when ON, makes a heck of a battery boost option.

Be sure to choose a quality switch that can handle the engine starter current. Blue Sea makes some good ones.

Manual Battery Switches - Blue Sea Systems

Re: Low voltage from alternator?

Reply #21 – July 02, 2021, 11:43:21 am

Quote from: Chuck & Jeannie – July 02, 2021, 11:38:59 am

Be sure to choose a quality switch that can handle the engine starter current. Blue Sea makes some good ones.

Manual Battery Switches - Blue Sea Systems

Agree, like and use a lot of BlueSea products.

The battery switch I used was Perko-- also a good brand. Rated 250 amps continuous, much higher intermittent.

Re: Low voltage from alternator?

Reply #22 – July 02, 2021, 07:57:28 pm

Quote from: Chuck & Jeannie – July 01, 2021, 12:27:11 pm

Here is what I think FWIW:

1. That Powerline 25-15 is a strange model number. I can't find it listed anywhere. I would like to see the original Hehr wiring diagram, but no luck so far?

I had the same issue. It also lists as a 25-26. I found this diagram just now. I honestly have not even studied it yet. I just want to try and respond to everyone's replies. See attached pdf digrams.

2. I believe you do have a sense wire. I think your factory wiring diagram is mislabeled. The wire B59 RD goes from the alternator to a 15 amp circuit breaker on your isolator panel. That circuit breaker (assuming it is not tripped) is connected to a post on the AUX start solenoid. That post is connected to the START battery post on the isolator. Therefore, wire B59 RD is HOT all the time and should be reading START battery voltage. It is a SENSE wire - not a EXCITE wire. An EXCITE wire is only hot when ignition switch is ON. The diagram for my coach was also mislabled in exactly the same way.

I will try to check this as soon as I can. The way I am parked right now I am not able to get under there and do any diagnostics.

3. I agree - the charging voltage is low. Should be more like 14.5 volts at the isolator alternator post, and about 13.8 at the (three) isolator battery posts. Your dash gauge should read START battery voltage (minus line loss in the wire from the batteries to the gauge).

Yeah I think it is low. It's hard to tell with the analog gauge on the dash but it looks closer to 12.5 than 13. That is too low!

4. If I am correct in my answer to #2, then you do not need a SENSE wire. It is possible the voltage regulator is not functioning properly, Or it is possible it is not reading the start battery voltage correctly. I think you would be better off having the SENSE wire connected directly to the start battery post on the isolator or even MORE better directly to the POS post on a start battery.

Will determine more after I can get back under the coach

5. You are correct - if those wires were for a Trik-L-Start then they were hooked up incorrectly. Should have been on the START battery post and (one of the) COACH battery posts.

Yeah that is what I was thinking.

6. I can't see the yellow wire good enough to comment. I need to see the official wiring diagram for your exact model alternator to know what wires should be connected where.

See the pdf I attached. What do you think?

Re: Low voltage from alternator?

Reply #23 – July 02, 2021, 08:01:04 pm

Quote from: wolfe10 – July 01, 2021, 12:50:40 pm

Not a bad choice if he does need to replace the diode-based isolator and wants to stay with an isolator rather than a going to a combiner.

This is the 3 bank version I would want to install to mimic the current one where the house bank runs off 2 banks. 3 bank Victron

But, his "fix" may be as simple as having a correctly wired sense terminal (from any location on the chassis battery side of the battery isolator). Lots less $$.

I am curious if this would "fix" my problem.

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Re: Low voltage from alternator?

Reply #24 – July 02, 2021, 08:02:48 pm

Quote from: Chuck & Jeannie – July 01, 2021, 06:08:41 pm

The thing is, Noah reports he is only seeing "13.6v out of the Alt to the isolator". Even if he wasn't losing ANY voltage between the alternator and the start battery bank, he would still have a problem.

13.6 volts will never fully charge his depleted start batteries. It might be enough to maintain fully charged batteries, however.

Noah reported (above) while on the road with generator running and boost switch engaged that dash volt meter only shows 13 volts. That is another suspicious data point IMO. If the generator is running, and the battery charger is turned on, and the boost switch on turned on, then I would expect to see above 14 volts on the dash volt meter. Something ain't right.

I agree this is low. I think I should be seeing higher voltage. I find it hard to believe I never see anything over 14v.

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