Boost switch, not boosting...

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Boost switch, not boosting...

June 22, 2012, 08:59:13 am

I've been out working on the coach for the last few weeks on and off. Since my last post about not starting after turning the engone off I've let it set for a while as I'm still challanged with shoulder surgery recovery.
Yesterday I conpleted the last of all new air brake lines and started her up. There were no squeeks from belts since tightening them about a month ago, so that was nice.
I decided to take her for a drive down the road and see how the brakes and air pressure worked. Everything seemed fine with that and I was happy.

While looking at one of the owners manuals a couple weeks ago I noticed that it said something to the effect of starting the engine and slightly raising the RPM's to a specific for a couple seconds and that would activate the "charging" of the alt causing an increase on the volt guage. Well, I noticed that when I started the engine.....there was no RPM's reading on the tach. ?? I checked where I thought fuses to be and made sure connections were good, so I don't know what's up with that

As I watched the air pressure build I noticed the volt guage was showing about 12-ish. I hit the boost switch and it didn't do anything. I have the unit plugged in, Trik L Start installed and not to long back I topped off the batteries with distilled water and tested their output. The batteries were all fine.
As I drove down the road I hit the boost switch and it did nothing at all again. I then started the gen and waited for it to kick in. Once it did the volts REALLY went up!! THEN, when I hit the boost switch it shot WAY HIGHER. I thought to myself, that's the way this thing should be working!!
So, what should I be checking and how should I do it?
We are heading to the U.P. In Michigan in a couple weeks and the last thing I need is to be stranded there...OR, anyplace else for that matter

It seems that we may have had this problem for some time and I never wanted to address it because I can and have ran the gen on most of our trips so we have appliances and A/C, TV etc.
It just seems like there should be an easy and simple fix for this, yes?
After I shut off the gen I watched the volts drop back down to what I've always known to be "normal". I hit the boost switch again with no gen running just to see what would happen and the guage went up just a "blip"....nothing really , but it did move. ( again, this was RIGHT AFTER turning off the gen )
I turned the boost off and on a couple more times right away and then it just stopped moving at all and stayed right where it had been before turning on the boost.
Just thought I'd give as much info about what I experienced so someone could have an exact idea of where to start repairing.

Shouldn't the boost switch BOOST without the gen running....like it does WITH it running?

Thanks in advance ya'll

Carl Sandel

Re: Boost switch, not boosting...

Reply #1 – June 22, 2012, 09:17:28 am

Carl,

Remember, the boost solenoid contacts are pulled in by 12 VDC. If battery voltage to it are very low, it is possible for a good solenoid to not operate properly. That is the only thing that comes to mind with the solenoid inoperable at lower voltage and operable at higher voltage. Certainly could also be a solenoid that is hanging up (contact area pitted) and the extra voltage was enough to overcome the contact.

I am more concerned with your lack of around 14 VDC with the engine operating when above idle RPM. Same for no tach reading. Were you still plugged in to shore power or generator on with converter still on? If so, it could "fool" the alternator's regulator into not working. I KNOW this happens on the charging system on our boat-- if 120 VAC charger is on, no tach reading and no change in voltage with engine running. Turning off the breaker to the charger brings everything back to "normal".

Brett

Re: Boost switch, not boosting...

Reply #2 – June 22, 2012, 11:43:55 am

I suspect the alternator or an open diode in the isolator and your boost switch is working properly. Here's why:

1. With the engine running you should see an increase in both the house battery voltage (as indicated on the video screen on the dash - at least it is on my coach) to above 13vdc AND an increase in the engine start voltage as indicated by the dial on the dashboard. This is because the alternator is wired to charge both batteries while it's running.

2. The generator, on the other hand, is wired to only charge the house batteries NOT the engine start battery UNLESS the boost switch is ON.

When you started your engine you were probably reading the dash voltmeter which only reads the engine start batteries. If you were also monitoring your house batteries on the video monitor you'd see no change in either; even with the boost switch ON.

As you drove down the road you started the generator. This would have begun charging the house batteries and the voltage on them would have increased (had you been watching). Then you hit the boost switch and the voltage on the engine start batteries increased because now the generator is charging BOTH sets of batteries. This indicates that the boost switch is doing what it's supposed to do: connect both sets of batteries.

With a 4-wire alternator the two larger connectors are the chassis ground and the alternator output. These have thick cables connected to them that may be black and red; or not. If you measure between these two large connectors while the engine is running (best use alligator clips applied before starting in order to be safe) you will see a voltage that is higher than 13vdc. You will see no voltage when the engine is not running (as you would on a car or truck system) because the isolator separates the alternator from the battery.

The other two wires on the alternator are smaller. One is the "sense" voltage that tells the regulator (integral with the alternator) what the battery voltage is so the regulator can adjust the output voltage appropriately. This is often labeled "field".

The other is the "ignition" which only has voltage when the ignition switch is on (key turned).

The alternator will not work if there is not approximately 12vdc on BOTH of these smaller terminals (but only one of them will have that voltage if the ignition is not ON).

Turn the ignition on (but don't start the engine) and measure the voltage on these smaller terminals; if you do not have about 12vdc on both of them then the problem is between the alternator and the batteries. If you have voltage on them but NOT between the two terminals with the large cables attached (the alternator + and - output) then the alternator is not working.

If you DO have voltage between the + and - terminals of the alternator when the engine is running then the alternator is working and putting out current and you have a problem with either the isolator or something else between the batteries and the alternator.

It's worth noting that on some coaches the two smaller connectors have been jumpered together so that the ignition switch applies voltage to both of them. This was the case with our system. The problem with this is that the ignition voltage comes through an isolator diode which drops the voltage by 0.6vdc so that the alternator "sense" is always lower than the real battery voltage. This can cause the alternator to work harder to bring the battery voltage up and since this creates more heat - and the alternator is already in a high heat area - it can cause failure. I re-wired the battery sense to the positive tab on the remote ignition switch.

Hopefully this covers all the bases. I've just gone through this and it was the alternator ($400 rebuild - next time I'll just buy one off eBay).

Craig

Re: Boost switch, not boosting...

Reply #3 – June 22, 2012, 01:07:33 pm

Quote

1. With the engine running you should see an increase in both the house battery voltage (as indicated on the video screen on the dash - at least it is on my coach) to above 13vdc AND an increase in the engine start voltage as indicated by the dial on the dashboard. This is because the alternator is wired to charge both batteries while it's running.

A posting here some time ago opined the alternator senses only the starter battery voltage. Not the house batteries.

Do you agree?

If so, then after a night of boondocking the generator is not needed to recharge the house batteries. And the alternator will not be taxed any more than if it charged the starter batteries only.

best, paul

Re: Boost switch, not boosting...

Reply #4 – June 22, 2012, 02:10:00 pm

Craig has it. When the main engine is running, both sets of of batteries are charged. Generator running, only house is charged. That's why I installed digital voltmeters where the CRT for the Audit was. Easy to see health of electrical system and turning on the boost switch equalizes the voltage or should if the boost switch is working. Voltmeters are less than $10/each out of China.

Pierce

Re: Boost switch, not boosting...

Reply #5 – June 22, 2012, 03:03:05 pm

Craig
Great explanation of charging, boost, alternator wiring.

Paul
Alternator senses just start battery voltage, but charges both start and house batteries (through isolator), so with discharged house batteries, alternator will work harder than if just charging start batteries. The amps going to the house batteries will cause the voltage of the start batteries to be slightly lower than it would be without the house batteries. If your house batteries are only slightly discharged at startup, they will be charged during driving about the same as the start batteries. However, if your house batteries were heavily discharged at startup, they will charge quit slowly while driving because the alternator charge rate is being set by the start batteries. This slow charging of house batteries while driving will also occur if amps are being drawn from the house batteries while driving (ie running refer from inverter). The best thing to do in this case is to set the boost switch after startup so that the voltage of all batteries are involved in setting the charge rate of the alternator.

I run my refer with the inverter when driving so that I can travel with the propane shut off, which is the law in some provinces in Canada. Some folks on this forum would say that I am abusing my alternator, however, I have been doing this for ten years and have had to rebuild the alternator about every 6 to 8 years. If it is a sunny day, the solar panels will keep the coach batteries charged, if cloudy, I set the boost switch. I check battery voltages at every stop and adjust as required.

I am not in El Centro now either, I am back in Canada. I will return to Slab City near El Centro just before Halloween. So, just when you least expect it, I will be knocking on your door.

Re: Boost switch, not boosting...

Reply #6 – June 22, 2012, 04:10:39 pm

Quote

Craig

Great explanation of charging, boost, alternator wiring.

Paul

Alternator senses just start battery voltage, but charges both start and house batteries (through isolator), so with discharged house batteries, alternator will work harder than if just charging start batteries. The amps going to the house batteries will cause the voltage of the start batteries to be slightly lower than it would be without the house batteries. If your house batteries are only slightly discharged at startup, they will be charged during driving about the same as the start batteries. However, if your house batteries were heavily discharged at startup, they will charge quit slowly while driving because the alternator charge rate is being set by the start batteries. This slow charging of house batteries while driving will also occur if amps are being drawn from the house batteries while driving (ie running refer from inverter). The best thing to do in this case is to set the boost switch after startup so that the voltage of all batteries are involved in setting the charge rate of the alternator.

I run my refer with the inverter when driving so that I can travel with the propane shut off, which is the law in some provinces in Canada. Some folks on this forum would say that I am abusing my alternator, however, I have been doing this for ten years and have had to rebuild the alternator about every 6 to 8 years. If it is a sunny day, the solar panels will keep the coach batteries charged, if cloudy, I set the boost switch. I check battery voltages at every stop and adjust as required.

Thanks, Wyatt. It took a few readings but I think I got it. But in my case I would not need to set the boost switch after starting. Based on James T's recommendation, I always use the boost when starting.

Quote

I am not in El Centro now either, I am back in Canada. I will return to Slab City near El Centro just before Halloween. So, just when you least expect it, I will be knocking on your door.

Good. We look forward to seeing you again. But don't delay. We expect to be on an airplane Nov 1 on our way to Can Cun / Paa Mul for our eldest daughter's second Iron Man (Iron Woman?) on the Isle of Cozumel (on Nov 25 I think)

best, paul

Re: Boost switch, not boosting...

Reply #7 – June 22, 2012, 04:14:28 pm

Quote from: Paul Smith – June 22, 2012, 01:07:33 pm

A posting here some time ago opined the alternator senses only the starter battery voltage. Not the house batteries.

Do you agree?

If so, then after a night of boondocking the generator is not needed to recharge the house batteries. And the alternator will not be taxed any more than if it charged the starter batteries only.

I agree that the alternator senses only the voltage at the end of the wire leading from the start batteries. This is likely to be some significant fraction of the actual battery voltage but never the actual voltage of the start batteries due to the resistance losses in that wire.

Because of this voltage drop the alternator will always be trying to charge the batteries (including the house batteries) but probably not working very hard to do so. This will probably be good for the house batteries if driving for a long period the day after boondocking but if you are just going short distances every day with significant loads on the house batteries it might be wise to consider driving with the boost on until the house batteries are fully charged.

The best way to check is to take digital voltage readings right at the batteries. But since this is a PITA I think Pierce's method of installing a separate digital voltmeter for each system is a good idea. The closer to the batteries the better (although so little current flows it's probably not much of a problem either way).

Craig

Re: Boost switch, not boosting...

Reply #8 – June 24, 2012, 11:27:07 am

I realized that there was more info needed to be supplied from my end after reading some of the posts so I went out and went through different steps and processes with the monitor on, key on, engine running and not, etc, etc. I wrote down all of the numbers and info.....and I think it went through the w3ash machine and dryer last night

I DO hovever have the tach working now. It was a loose connection in the dash I believe. I wiggled a couple wires and WHALA! Wish it was that way with other stuff

I will find the info out in the barn if it didn't in fact go through the laundry and report back. If it did....I will go back through the process again and supply the info later today if possible.

Carl Sandel

Re: Boost switch, not boosting...

Reply #9 – June 24, 2012, 09:02:35 pm

Can you put a volt meter on the house batteries when the coach is plugged in to see if they are being charged while plugged in? Alos did you have the disconnect switch turned off while the coach was in the barn? I sounds like your boost switch is working, but also need to know what the engine battery shows for voltage when the engine is running. There seems to be something missing.

Re: Boost switch, not boosting...

Reply #10 – June 24, 2012, 11:22:10 pm

Basic 12VDC system check:

1. With shore power and generator OFF, check voltage at CHASSIS and HOUSE batteries. 12.7 is fully charged, 12.2 is 50% discharged. Anything over 12.7 is surface charge.
2. With shore power ON, check voltage at CHASSIS and HOUSE batteries. House bank should jump to 13.2-14.2 depending on charger. OE, Foretravel was not wired to charge the chassis battery from converter, so it's voltage should not change.
3. Should have exactly the same results as in #2 on generator power.
4. With shore power and generator OFF, start engine and raise RPM to 1,11- 1,200. Both house and chassis should be 13.5-14.2.

Let us know your readings.

Brett

Re: Boost switch, not boosting...

Reply #11 – June 24, 2012, 11:41:24 pm

Nice!! Will do, thanks Brett

Re: Boost switch, not boosting...

Reply #12 – July 01, 2012, 02:30:11 am

Ok, finally now that some other repairs are complete that would not allow me to start the engine, I have tested and logged all information having to do with the charging and electrical system. It would be great if someone can look at the numbers and method for testing and let me know that everything is not only working fine, but from the looks of it, everything is GREAT!!
I currently have a Greenlee Digital DM-20 tester and here's what I've found,

6/30/12
Shore & Gen OFF
Both house batteries 13.28
Chassis 13.09

Shore ON
Both house batteries 13.35
Chassis13.12

Shore ON, BOOST ON, Floor switch OFF
Both house batteries 13.35
House 13.04-.06

Shore ON, BOOST ON Floor switch ON
Both house batteries 13.34
Chassis 13.27

Gen ON, BOOST ON, Floor switch ON
Both house batteries 14.57
Chassis 14.54

Gen ON, BOOST OFF, Floor switch On
Both house batteries 14.74
Chassis 14.41

Gen ON, BOOST OFF, Floor switch OFF
Both house batteries 14.72
Chassis 14.39

Fresh Shut Down, Nothing On, No Shore, No Gen, Floor switch OFF
Both house batteries 13.59
Chassis 13.37

Engine Running, BOOST OFF, Floor switch on
Both house batteries 12.65
Chassis 12.37

Engine Running, BOOST ON, Floor switch ON (dash gauge showed nothing when hit boost switch)
Both house batteries 12.64
Chassis 12.45

I know this is more infor than Brett posted to test last week, but I figured since I was there I would log every possible option I could think of so if something didn't seem right, it could be addressed.

Please let me know what ya'll think.

Re: Boost switch, not boosting...

Reply #13 – July 01, 2012, 10:06:07 am

Quote from: Carl Sandel – July 01, 2012, 02:30:11 am

Ok, finally now that some other repairs are complete that would not allow me to start the engine, I have tested and logged all information having to do with the charging and electrical system. It would be great if someone can look at the numbers and method for testing and let me know that everything is not only working fine, but from the looks of it, everything is GREAT!!
I currently have a Greenlee Digital DM-20 tester and here's what I've found,

6/30/12
Shore & Gen OFF
Both house batteries 13.28
Chassis 13.09

THIS WOULD SUGGEST THAT YOU RECENTLY HAD BOTH BATTERIES CHARGED BY SOME MEANS, AS BOTH HAVE A SURFACE CHARGE IN ADDITION TO FULL CHARGE.

Quote

Shore ON
Both house batteries 13.35
Chassis13.12

THIS WOULD SUGGEST THE CONVERTER OR CHARGER IS CHARGING THE HOUSE BANK ONLY--HOW THE SYSTEM WAS SET UP. AGAIN, IF YOU HAD TURNED ON SOME 12 VDC LOADS TO LOWER INITIAL BATTERY VOLTAGE, THE DIFFERENCE IN READINGS WOULD HAVE BEEN MORE DRAMATIC.

Quote

Shore ON, BOOST ON, Floor switch OFF
Both house batteries 13.35
House 13.04-.06

ASSUME THE BOTTOM "HOUSE" IS ACTUALLY THE CHASSIS BATTERIES. THIS WOULD SUGGEST THAT THE BOOST SWITCH/SOLENOID IS NOT WORKING. NEED TO TROUBLESHOOT THE SOLENOID.

Quote

Shore ON, BOOST ON Floor switch ON
Both house batteries 13.34
Chassis 13.27

THIS WOULD SUGGEST SOME STRANGE WIRING IMO. UNUSUAL FOR THE BOOST FUNCTION TO GO THROUGH THE HOUSE BATTERY DISCONNECT SWITCH (AT LEAST I ASSUME THAT IS WHAT FLOOR SWITCH REFERS TO).

Quote

Gen ON, BOOST ON, Floor switch ON
Both house batteries 14.57
Chassis 14.54

ALL NORMAL-- ALTERNATOR IS CHARGING BOTH BANKS. CONTRADICTS READINGS BELOW.

Quote

Gen ON, BOOST OFF, Floor switch On
Both house batteries 14.74
Chassis 14.41

NOT SURE THE DROP IN CHASSIS BATTERY VOLTAGE IS INDICATIVE OF A PROBLEM-- COULD BE IF THE DROP BECOMES MORE SIGNIFICANT LET US KNOW.

Quote

Gen ON, BOOST OFF, Floor switch OFF
Both house batteries 14.72
Chassis 14.39

COULD STILL BE SURFACE CHARGE FROM RUNNING ENGINE/CHARGING WITH ALTERNATOR.

Quote

Fresh Shut Down, Nothing On, No Shore, No Gen, Floor switch OFF
Both house batteries 13.59
Chassis 13.37

Engine Running, BOOST OFF, Floor switch on
Both house batteries 12.65
Chassis 12.37

CONTRARY TO EARLIER READING WITH ALTERNATOR CHARGING. ASSUMING THIS WAS AT RPM ABOVE IDLE, THE ALTERNATOR IS NOT CHARGING. READ VOLTAGE AT ALTERNATOR-- AGAIN WITH ENGINE AT 1100 RPM OR SO.

Quote

Engine Running, BOOST ON, Floor switch ON (dash gauge showed nothing when hit boost switch)
Both house batteries 12.64
Chassis 12.45

ALTERNATOR NOT CHARGING

Re: Boost switch, not boosting...

Reply #14 – July 01, 2012, 10:16:04 am

Okay... only a couple of these tells the tale.

This one:

Quote from: Carl Sandel – July 01, 2012, 02:30:11 am

Gen ON, BOOST ON, Floor switch ON
Both house batteries 14.57
Chassis 14.54

And these two:

Quote

Engine Running, BOOST OFF, Floor switch on
Both house batteries 12.65
Chassis 12.37

Engine Running, BOOST ON, Floor switch ON (dash gauge showed nothing when hit boost switch)
Both house batteries 12.64
Chassis 12.45

Please let me know what ya'll think.

They tell me that your alternator is not charging anything. Your next step would be to remove it and have a local shop put it on a test bed and see if it's working. If not, have it rebuilt. If the alternator is working on the test bed we'll go from there.

Craig

Re: Boost switch, not boosting...

Reply #15 – July 01, 2012, 10:35:17 am

These all the results of a coach that sits for long periods of time without exercise. Please take care of the coach by exercising it once a month on the road for approximately 30 miles. Run every feature that is in the coach including propane systems.

The alternator is heavily taxed when the engine is started with low batteries, both coach and start.
Peter

Re: Boost switch, not boosting...

Reply #16 – July 01, 2012, 11:27:43 am

Ugh! ..... I forgot to turn on my monitor / camera and check VDC readings along the way.
Brett, you are right about my post that had "house" listed twice....it was supposed to be Chassis.
Yes, when I listed Floor switch that is "HOUSE BATTERY DISCONNECT SWITCH" .. I didn't know what it was called

I NEVER raised the RPM....DOG GONE IT!

I will print this info off and go back out today and gather more info.
Just curious, on which test should I actually raise the RPM for a specific test? The engine was at idle the whole time the engine was in running mode for the above. Please advise.
Where is the solenoid you mentioned when you said I need to "NEED TO TROUBLESHOOT THE SOLENOID"? Would it be back in the engine compartment where my Trik L Start is mounted?
Please advise for that as well so I can test this and replace if needed. It sounds like once I can find it, it shouldn't be a hard thing to do.

I'll report back in a while. Thanks SO MUCH

Re: Boost switch, not boosting...

Reply #17 – July 01, 2012, 11:31:43 am

Although the coach sits for long periods of time it is always plugged into shore in a barn with Trik L Start.
Is this bad?
Should I unplug the system for a certain number of days during the month?
I don't want to waste electricity and really don't want to fry something.
Peter, I will get better at getting her out and driving as you say for a minimum of 30 minutes while running appliances and such.

Re: Boost switch, not boosting...

Reply #18 – July 01, 2012, 11:40:32 am

Carl,

RPM should be raised to high idle on all test of the alternator.

I don't know where the boost solenoid is located on your coach. In mine, it is next to the batteries.

To troubleshoot a boost solenoid:

It will have two LARGE lugs-- one to each battery bank (chassis and house).

It will have either one or two small terminals. If one, it is the positive/signal wire. If two, one is ground, the other is the positive/signal wire. On the one terminal solenoids, the body of the solenoid serves as the ground.

With the switch off, voltage at each of the large lugs should be DIFFERENT, reflecting the difference in voltage of their batteries. And the positive signal wire should have no voltage.

With the boost switch ON, the signal terminal should have 12+ VDC and the two large lugs should have the same voltage.

If voltage is still different on the two large lugs, and you do have 12+ VDC on the signal terminal, the solenoid is bad. If no voltage on the positive signal terminal, you have a problem with a fuse, the switch or wiring. To verify that both this AND the solenoid are not bad, remove the wire from the signal terminal and take a small jumper wire from either large lug to the signal terminal. A small wire is all you need as you are only talking about 1-2 amps. The solenoid should not "CLICK" and the two large lugs should have the same voltage.

Brett

Re: Boost switch, not boosting...

Reply #19 – July 01, 2012, 11:50:38 am

Quote from: Carl Sandel – July 01, 2012, 11:27:43 am

Just curious, on which test should I actually raise the RPM for a specific test? The engine was at idle the whole time the engine was in running mode for the above. Please advise.

Strictly speaking, the engine RPM should be raised in order to be sure that the alternator is working properly. So any time you have the engine running you should do the test with the RPM raised. Having said that, on my U225 the alternator starts charging both sets of batteries as soon as it's started. But sometimes they need the RPMs raised in order to kick in.

In this case I strongly suspect no difference but the i's and the t's have to be taken care of.

Regarding your question about unplugging the coach... as long as you are using 3-stage chargers (including the Trikle-Start (sp?)) I don't think that unplugging anything will do any good. It wouldn't do any harm... but probably no good.

Aren't motor homes FUN???

Craig

Re: Boost switch, not boosting...

Reply #20 – July 01, 2012, 12:13:40 pm

Brett
I acknowledge you for your infinite patience, your practical wisdom, and your willingness to help eager newbies who are having difficulty understanding the very complicated electrical assemblies in our Foretravel motorhomes.

I value highly, your tireless contributions to Foreforums.

Re: Boost switch, not boosting...

Reply #21 – July 01, 2012, 12:36:25 pm

Quote from: P. Wyatt Sabourin – July 01, 2012, 12:13:40 pm

Brett
I acknowledge you for your infinite patience, your practical wisdom, and your willingness to help eager newbies who are having difficulty understanding the very complicated electrical assemblies in our Foretravel motorhomes.

I value highly, your tireless contributions to Foreforums.

+1 to that. And not just this forum either. All I needed to do was read some of the total nonsense posted on another forum to realize how valuable Brett is.

And having said that, let me add that the level of expertise and the general tone of this forum puts it on a much higher level than most.

Not to mention that technically the forum is ideal.

Craig

Re: Boost switch, not boosting...

Reply #22 – July 01, 2012, 12:47:00 pm

Brett, I would like to add my thanks to you as well. Your posts have been very helpful. I sure hope you will be able to continue while at sea. Dick

Re: Boost switch, not boosting...

Reply #23 – July 01, 2012, 02:10:58 pm

Wow, thanks guys.

Brett

Re: Boost switch, not boosting...

Reply #24 – July 01, 2012, 02:14:23 pm

Modest, too!

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