Alternator doesn't charge house batt until press emerg start

wa8yxm wrote:
Your isolator is not working.. This consists of two parts on MOST RV's one on a very few. I will describe both.

Most common.. A Solenoid (Also called a Relay or Contactor but in this use Solenoid is the most common name) and a controller for it.

Depending on the controller, it may be a one-way (Engine charges house) or it may be a bi-directional like min (Both charge).

The simple ones may or may not have a delay and sense the ingnition lead.

The more complex ones measure voltage and when the see 13+ they engage

To test you need to find the isolator relay and measure the voltage on the SMALL screws. (the big ones are battery leads) you should see voltage within one minute of starting the coach.. And that voltage may appear and dissappear depending on teh system.. But I suspect it will be constant.

My system does not have a built in delay. The solenoid has a single small screw with two wires attached. One of those wires goes to the emergency start switch (which works) and the other goes - probably - to the ignition. That wire has a bad connection somewhere and isn't getting power to activate the solenoid while the engine is running.

The solution that I am considering is running a wire from a fuse tap (from a fuse that's only energized when the engine is on) to the wire going out from the emergency start switch. The fuse box is right next to the emergency start switch, so the wiring would be short and simple. Is there any problem with that setup? Would there be a problem using the emergency start switch in that case?

Your isolator is not working.. This consists of two parts on MOST RV's one on a very few. I will describe both.

Most common.. A Solenoid (Also called a Relay or Contactor but in this use Solenoid is the most common name) and a controller for it.

Depending on the controller, it may be a one-way (Engine charges house) or it may be a bi-directional like min (Both charge).

The simple ones may or may not have a delay and sense the ingnition lead.

The more complex ones measure voltage and when the see 13+ they engage

To test you need to find the isolator relay and measure the voltage on the SMALL screws. (the big ones are battery leads) you should see voltage within one minute of starting the coach.. And that voltage may appear and dissappear depending on teh system.. But I suspect it will be constant.

I didn't splice that particular circuit as I was concerned that it would not operate unless the emergency start switch was toggled .. the run from the Ford fuse box to the solenoid was only a few feet in my rig so minimizing wire was never a factor.

ksg5000 wrote:

jayhorowitz wrote:

ksg5000 wrote:
In my Fleetwood Jamboree the isolator solenoid should engage when you turn the ignition key - you may have wiring or fuse issue. When I had similar problem I just ran a wire from an empty slot in fuse box through fire wall grommet to the solenoid - the fuse slot of use energized with key turning so it was a quick/inexpensive fix.

Clever fix. Did that mean running a wire all the way from the engine power distribution center to the house battery compartment? ...

As I recall I purchased a "piggyback" fuse and used the radio fuse slot - mine was located near the drivers left knee - ran a wire through a nearby grommet. My rig had an old fashion battery isolator solenoid with 3 lugs - the middle one was used to power up the solenoid and that's where I attached the wire.

After a lot of time tracing wires, looking at diagrams and trying things this is the solution that I think I'm going to run with, seeing as the solenoid is operational (with the emergency start switch) and it looks as though the ignition-activated wire to the solenoid simply isn't giving the solenoid juice. (And I can't seem to trace it into the engine compartment.)

To minimize the length of wire that I need to run I was thinking about tapping one of the fuses by the driver's left knee and splicing that wire into the one coming out of the emergency start switch, which is already wired to the solenoid and is right near the driver's-left-knee fuse box. Does that sound reasonable?

A common 11880 steel can Ford type "solenoid" with silver contacts and a 36 ohm coil will instantly fail if a 200+ ampere load is applied across the load contacts.

A five dollar phenolic case Ford starter solenoid is rated for 800 amperes make or break for thousands of cycles. But with a 2.0+ ohm coil is will overheat after a few minutes and fail.

The tower-type Trombetta solenoid is generically referred to as an "Essex Type" solenoid. They are a definite design improvement over the Ford style solenoid.

To avoid make and break flashover deterioration of the contacts, serious solenoids are mercury filled.

Some posters are missing the point. A solenoid has a definite design limit on capacity. Make and break flashover is the major cause of solenoid contact failure.

NUMBER OF CYCLES, make and break at load is a crucial value.

Gear reduction (planetary gears) is becoming more common and it is needed. When did Chevrolet and Ford 454 and V10 engines switch to planetary gear reduction starter motors?

The Trombetta solenoid should solve your problem - probably "for good", as it did in my case. Note that this continuous duty solenoid is also rated for up to 600 amps of inrush current.

It's a bit larger than the stock one, so I had to do some fancy finger contortions and creative wire routing to fit it into the same space in the steel enclosed distribution box where Winnebago intents for it to be. So far it has just sat there doing it's thing year after year - it doesn't even make as loud a "thump" as the original one did when I turn the ignition key.

For what it's worth, I have a permanent four-place resolution voltmeter mounted on the dash in the cab that constantly shows the voltage on the coach's 12 volt system (monitors system voltage AFTER the coach battery disconnect switch). That's how I discovered that the alternator was not always getting hooked up to the coach batteries after starting the engine.

This voltmeter also tells me whether or not I remembered to turn the coach battery disconnect switch back ON, after gassing up, so our food in the refrig isn't warming up when going down the road.

pnichols wrote:
I changed to this solenoid years ago with silver alloy contacts to stop this corrosion and pitting. The coach batteries now arrive at our camp sites nicely and quickly refreshed:

http://shopping.murcal.com/Catalog/Bear-DC-Contactor-Family/114-1211-020;jsessionid=0a010c471f43e3c1a11ecc744d4b88c1f3921dcee21e.e3eSch4MaN4Re34Pa38Ta38Naxf0

pnichols - Thank you for posting the link!

I have replaced the "Battery Mode Solenoid" in our 2003 Minnie 324F twice as the batteries do not reliably get charged by the alternator. The new one always works for a year or so then it sometimes it works, sometimes not. I hear the "clunk" when turning on the ignition, but often don't get charging voltage from the alternator at the house batteries.

I'm hoping that this new solenoid solves the problem.

MEXICOWANDERER wrote:
BTW a hot non gear reduction starter motor starting say a 454 Chevrolet engine at 20 degrees can draw in excess of 400 amperes inrush and break.

For What It's Worth: I believe that all over the world engine starter motors are geared down. They connect to a large diameter ring gear that has a diameter much larger than the diameter of a little tiny gear on the starter motor's shaft - hence a healthy "reduction ratio" is, in fact, being used to couple the starter motor to the engine's driveshaft.

The garden-variety interconnect solenoid on our Class C motorhome begun to only intermittently charge the coach batteries a couple of years after we had owned the rig. Sometimes the coach battery terminals had over 14.XX volts on them (from the alternator) right after starting the chassis engine ... and sometimes they showed only the normal 12.XX volts from their own at-rest voltage right after the chassis engine was started.

However, this solenoid always "clicked/clunked" whenever I turned the ignition switch. I figured that the solenoid contacts were closing, but making only intermittent good high-current electrical contact due to the contacts being corroded and/or pitted.

I changed to this solenoid years ago with silver alloy contacts to stop this corrosion and pitting. The coach batteries now arrive at our camp sites nicely and quickly refreshed:

http://shopping.murcal.com/Catalog/Bear-DC-Contactor-Family/114-1211-020;jsessionid=0a010c471f43e3c1a11ecc744d4b88c1f3921dcee21e.e3eSch4MaN4Re34Pa38Ta38Naxf0

Sure, this relay costs around $35 more than the stock one Winnebago installed ... but having properly cared for coach batteries that you can rely on for years is priceless ... and having this relay not failing to do it's thing time after time is a step in that direction, IMHO.

MEXICOWANDERER wrote:
I get passed on highways by cars running on emergency spare tires at 80 mph. Just because I don't see them do somersaults off into the canyon does not mean the practice is the most intelligent. Hell my uncle in Montana controlled a pedestal grinder with a foot dimmer switch, and down here an English National Geographic magazine stands a good chance of being dismembered in an outhouse. A friend loaded his '50 Chevy pickup with three and a quarter tons of asphalt and limped six miles to his house to pave his driveway. IT WORKED! Is this abuse "recommended"?

Relays have ratings. The ratings including duty cycle should be obeyed. The only constant duty 12-volt relay I know of rated for 400 amperes break costs around two hundred dollars. "It Works!" is probably the biggest screw-up in the English language. It leads to "It Doesn't Work!" and that is guaranteed to happen at the worst freakin' possible time.

Do it right por favor. Find the ratings and obey them. BTW a hot non gear reduction starter motor starting say a 454 Chevrolet engine at 20 degrees can draw in excess of 400 amperes inrush and break. Guesswork leads to disappointment.

Motorhomes last 35 years
1. use a BIG BOY solenoid, rated at 200 amps continuous duty and is found on almost ALL RV Diesel motorhomes
2. The simple Ford(starter solenoid) looking Silver solenoid (NOT FORD but looks like it), can have either 4 posts or 3 posts, rated at 100 amps. COMMON on almost all Gasoline Motorhomes and some older Diesels. THIS solenoid is rated at continuous duty and the LARGE amp draw to start a chassis engine for a few seconds.
3. IF you look at a Auto parts catalogue, you will see hundreds of silver solenoids that all look the same, the problem is, they ALL have different specs and ratings and operation. Just buying a solenoid that "looks" like the one you have without knowing what its rating is will be a cause for failure. THIS IS A COMMON PROBLEM I SEE.
4. Except for very few large Diesels, all the Battery disconnect relay's are rated at no more than 100 amps continuous duty. That is why you never connect an Inverter or the emergency start circuit thru one.
4. Mexwanderer, I don't know if you are posting stating that ALL motorhomes are not designed right or you are just shooting your knowledge out there. Doug

I think these have been wired in several different manners (or have been re-wired by other owners). I have a 23' Tioga that has a similar setup. However mine has a solenoid that apparently is a constant-duty model. It was wired so that pressing the button (engine off) will close the relay and releasing it will open the relay.

What I thought was odd though is that it was wired to the ignition switch so that when you start the engine the relay closes when the keyswitch gets to "on" and stays closed until you turn the engine off. So the both house and chassis batteries are always charging off the alternator when the engine is running.

I ended up replacing the button with a lighted toggle switch so I can control the process. I can manually engage it to charge the house battery off the alternator and also engage it to charge the chassis battery from the converter.

But now I don't have to load the alternator with a low house battery when starting and warming up the engine.