Skip to main content ↑ ↓
Topic: Charging issues (Read 2771 times) previous topic - next topic

Charging issues

Not really a new subject and I have read most everything in here on the subject. I just doing homework before I start digging into it.
Our 98 u270 (had it home 3 weeks) is having a charging issue and has a history of eating alternators. By the records I count 4 and she only has 45,000 miles. PO said that he put one on it 4 or 5 years ago. Yeah but he put like 500 miles a year on the coach. They last longer than that.
She stopped charging on me on the way home and I put an alternator on and it got us home. Even with a new 160 amp Bosch replacement the volt meter only showed 11.5 volts (no I haven't double checked with a meter yet). The posts on the new alternator were in a different position but I'm pretty sure I hooked it up right. There is battery, ignition and the other one! But I was in a gas station parking lot mid Atlanta. Stressed with a coach that wouldn't move. No electricity no gears! Ask me how I learned this lesson.

When we got home I purposely didn't plug it in. All the batteries are 4 years old so I wanted to see how they did. After sitting 3 weeks, she cranked right up. After running a while I noticed it was only charging 10 volts. Gauges were running amuck, auto level wouldn't work right tach pegged itself on 3000.Turned it off and sure enough she would not crank back without the boost button. So I know she was sucking from the batteries and lacking voltage.
A quick look through all the cables and everything appears dry, clean and tight. This coach is really clean underneath. Zero rust on anything, even the battery trays with wet batteries still have most of their paint.
I know I need to up my automotive electrical testing game a bit.  I can wire houses all day but they don't have diodes and batteries and olms don't mean much there, its hot or its not. I understand that the isolator may be a good place to start. I'm not in a rush and I'm a pretty fair mechanic so I feel I should be able chase this down myself. I have a lot of things that need attention so don't be surprised if you see me start multiple posts.
Any help guidance or just moral support is well appreciated.
I am also new to this forum and if I do a no-no, just correct me and lead me. My wife says I'm trainable, with patience!
Thanks so much,

Re: Charging issues

Reply #1 –
Not going to be much of a help, but figure anytime an alternator fails so often, the problem is likely outside of the alternator. But it is true there are some poor rebuilt alternators sold out there, as they only replace broken parts, so most of us like to find a local small rebuilder and keep our original, but that is too late for you.

Motorhomes have isolators that allow alternator to charge house & start battery banks, while keeping the two banks "isolated" from each other. In this case the alternator requires a separate small-wire that directly reads house battery voltage as the isolator keeps the alternator from seeing either battery voltage on its output cable. Foretravel uses another small-wire to 'excite' the alternator with ignition voltage. Normally our coaches require a not real popular. style of alternator called "Duvac" that has both of these two small wire connections on the back of the alternator's voltage regulator.

Sometimes, usually out of ignorance, non-Duvac alternators are installed with work arounds for the voltage sense and excite wires. And other times the two small wires are reversed or any combination of messing up.

Most alternators also have three styles of built-in voltage regulators: variable, 3-step, fixed. If using a diode-based isolator (most common), with the isolator's diodes reducing alternator voltage, the alternator usually outputs a higher-than-normal voltage, which after the isolator is lowered to a more friendly voltage for charging batteries.

I am writing because we all face a broken alternator at inopportune times and a readily available temp fix can keep us rolling for weeks if we want:

Run generator while driving, turn boost switch on, and let the inverter/charger power the start battery bank via the boost solenoid. Many of us have used this simple bypass for weeks until we get back to an opportune time to fix our alternator.

Hope you get to the bottom of alternator musical chairs.

Re: Charging issues

Reply #2 –
If replacing the OEM alternator with another brand, make sure the pulleys are the same diameter. Alternators don't care for overspeeding. Most alternators from cars have small pulleys so they charge in stop and go traffic.  Make sure the belts are not too tight. You should be able to rotate the belt 90 degrees with your fingers mid-span.

Pierce

Re: Charging issues

Reply #3 –
Find the Isolator and try bypassing it .  It has 3 post.  Connect the alt  wire to the engine battery post .  And go from there.  IMHO

Re: Charging issues

Reply #4 –
Barry, we bought a direct replacement alternator i gave them the leese neville# number out of the  FT manual!  They crossed to brand new bosch 160 amp $500 one and i still have my old one, but it wasnt an original!. Had three wires, a big one(battery) and 2 small ones. The post marked I on the new one(marked ign on the old one) and as i said before, the other one! Not sure what it is or where it goes.
Our coach is going to need some love before we get her too far from home so she is sitting beside the shop plugged in for me to service everything and figure this out.
Im lost at the exciter wire! If i read correctly the alternator should be charging 14 .5 ish volts which is higher than the average car right? (12.5 ish volts)
Im gonna need to freshen up my meters and testing skill sets.

Re: Charging issues

Reply #5 –
Do you think a Leece-Neville alternator would help is issue?

Re: Charging issues

Reply #6 –
I saw a isolator for a fair price,.should i just buy the darn thing? Im gonna have the old alternator rebuilt and have a spare.
Belts fine and it has an idler pulley no i cant really adjust it. i used the old alternators pulley so it should be spinning correctly.

Re: Charging issues

Reply #7 –
Jim, napa said that was a direct replacement for the leece neville. IDK,.has a 2 year warranty if its not right!

Re: Charging issues

Reply #8 –
Replacement alternators have caused many problems for Forum members.  If the person buying, or replacing, the alternator does not understand the Foretravel diode isolator charging system then they often end up either installing the wrong alternator or screwing up the wiring...or both.

Look at the diagram below.  This is a screen shot taken from the top right corner of the B-2179 12 Volt Wiring Diagram, found in our Forum library.  It shows a (U320) DUVAC alternator wiring setup, which is similar to the one installed in your U270 coach when it left the factory.

https://www.foreforums.com/index.php?action=media;sa=media;in=3300

Look at the DUVAC alternator in the diagram.  It has 4 terminals on the back.  The two large terminals are the B+ output, and the negative (-) ground.  The B+ cable connects to the center post on the battery isolator.  The negative ground cable connects to a large grounding bolt on the engine block.

The other two terminals are smaller.  One terminal, usually marked SENSE (S) connects to a circuit breaker and then to the engine START battery post on the isolator.  The other small terminal, called the "exciter", is usually marked IGN and goes into the wire loom where it eventually connects to a 12 volt power source that is only hot when the ignition switch is in the ON position.

These two small alternator terminals must be present and properly connected in order for your original OEM charging system to operate.  If the alternator on your coach does not have these terminals, then it is not a DUVAC alternator.  It is possible to make a non-DUVAC alternator work on your coach, but it requires modification of the stock wiring and/or a different type of battery isolating device.

If you post a photo of the back side of your alternator, it'll help us figure out how to get your charging system working.  Don't start buying parts until you understand what you have now and if it can be made to work.



Re: Charging issues

Reply #9 –
The link below takes you to a post (Reply #17) with photos of a OEM Leece Neville DUVAC alternator, just like the one that originally came on your coach.

Alternator, Isolator or both?

Re: Charging issues

Reply #10 –
Thanks so much im gonna print and check through all this and see where im at. Unfortunately Saturday night i was.lucky to find anything much less an exact replacement. It may be that i need to go back to that very thing. Im not trying to upgrade. Just want it working and fixed!

Re: Charging issues

Reply #11 –
If you can post the model number off the ID plate on your Bosch alternator that would help us help you.

Re: Charging issues

Reply #12 –
I dont have access to the back of the alternator tonight.
I do have the bosch part number and the paperwork that was enclosed if i can figure out how to attach on here from my phone. Which does not appear to be possible! Is this not possible?
Its a bosch AL9960LH

Re: Charging issues

Reply #13 –
Here's a picture of the back and a description of it.

AL9960LH - STS Diesel

Re: Charging issues

Reply #14 –
The Bosch AL9960LH alternator is a self-excited "1-wire" model.  It does not have a SENSE terminal.

The "I" terminal is a INDICATOR connection.  It is NOT a (hot with ignition switch ON) "EXCITE" terminal.  Connecting the "I" terminal to a 12 volt source may damage the alternator or the internal regulator.

This alternator is NOT suitable for use with a diode based battery isolator.  As noted earlier, it is possible to make this alternator work, but it will require modification of the OEM charging system.

Re: Charging issues

Reply #15 –
Quote from: Wpduffey –
Im not trying to upgrade. Just want it working and fixed!
If you still feel this way after "sleeping on it" then I can suggest a couple different options.  It is up to you to decide if either one is of any interest.

Option 1:  Keep the Bosch alternator and make it work.  A "1-wire" alternator is designed to be very simple to install.  All it requires is one output wire (hence the name) which is connected directly to the engine start battery.  The alternator grounds through the mounting bracket.  You could replicate this "1-wire" alternator connection on your coach by following Mike's (Protech Racing) earlier suggestion to "Find the Isolator and try bypassing it.  It has 3 posts.  Connect the alt wire to the engine battery post."  You would remove any other wires that are now attached to the alternator.  By doing this you will have the Bosch alternator correctly wired, and (assuming it is not damaged from prior incorrect wiring) it should function properly.  However, it will only charge the engine start batteries.  Depending on how you plan to use your coach, this might work fine.  If you plan to normally stay in RV parks with shore power hookup, then your house (coach) batteries become much less important.  They will be charged by your inverter/charger when you are connected to shore power (or running your generator), and they should have plenty of power to run the coach appliances when driving down the road.  As a backup, you can always use the BOOST switch to connect both battery banks when the engine is running.  With the BOOST switch on, both start and house batteries will be charged by the alternator.

Option 1 with a upgrade:  You can keep the Bosch alternator and replace the OEM diode based battery isolator with a different type of device, commonly called a "Smart Combiner".  There are several to choose from.  They can vary in price and complexity.  Going this route will allow your charging system to operate automatically just like the original design, but with improved efficiency and some additional benefits.  Forum members have a lot of experience with this kind of modification, and can help you with the choice of product and installation.

Option 2:  Replace the Bosch alternator with a proper DUVAC model.  Going this route will return your coach to the factory original automatic charging design.  In all likelihood your battery isolator is just fine - we can tell you how to check it for proper operation.  You will also need to verify that both the SENSE wire and the EXCITE wire are still present on your coach, and still connected correctly.  This is also easy - we can tell you how.

You need to decide how you want to operate your coach, and how you want to correct the problem with your charging system.

Re: Charging issues

Reply #16 –
And, a third option that is NOT automatic is to go KISS theory and install a simple marine ON-OFF switch.

Alternator B+ and chassis battery cable to one lug and house battery cable to the other lug.

ON, both battery banks are charged (by either alternator or inverter/charger). Also, high-amp "boost" function.

OFF and only chassis battery is charged from the alternator.

I installed mine at the foot of the bed so easy to select from inside.

Diode-based isolator in the trash.

Re: Charging issues

Reply #17 –
Wow thanks so much guys, so much great information.
I am a KISS kind of guy but in this case I am going to make a few calls and see if I can get my money back from NAPA since what they sold me is not truly correct. then go from there.
Thanks again,

Re: Charging issues

Reply #18 –
Yup, with a diode-based battery isolator, you MUST use an alternator with external SENSE WIRE.

Since the sense wire is on the chassis battery side of the isolator, it insures that the batteries receive the correct voltage.

Re: Charging issues

Reply #19 –
Quote from: Wpduffey –

She stopped charging on me on the way home and I put an alternator on and it got us home. Even with a new 160 amp Bosch replacement the volt meter only showed 11.5 volts (no I haven't double checked with a meter yet).

When we got home  . . .
After running a while I noticed it was only charging 10 volts. Gauges were running amuck, auto level wouldn't work right tach pegged itself on 3000.Turned it off and sure enough she would not crank back without the boost button. So I know she was sucking from the batteries and lacking voltage.


You need to find out where all of those electrons are going.

One way to to disconnect all electric loads, then add them back one by one.

Quick question out of no where:  Are you running something big on your inverter?

Remember: When the alternator reaches it's current limit, the voltage regulator rolls back the voltage to keep the current flow in check.

"Something" is using a lot of power.