Charge house batteries with Alternator

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Charge house batteries with Alternator

May 01, 2011, 12:48:42 pm

Paul:
This is a reponse to your reply to the RV GPS topic, this is a new topic:

Why run your generator in the morning when your alternator will charge your house batteries while you drive if you turn on the boost (which connects start/house batteries together).

One caution: if house batteries are very low then high current can flow from start batteries to house batteries and overload boost relay as well as deep cycle your start batteries. You can get a fairly accurate idea of what this load will be if you check the house batteries voltage and the current being drawn - private email if you want more info.

I know that many folks on the site believe that it will wear out or overheat your alternator if you make heavy use of it. I do not share this philosophy. I have successfully run my refrigerator with the inverter when driving for years. I dismantled and cleaned the alternator in my 96 U320 because the sensing wire connector was rusted and not connecting. I believe this alternator is original with 95,000 miles. The wear on the brushes was minimum, and bearings were silent. Three days ago I left California and arrive in Canada yesterday while running the refrigerator with the inverter. Checked alternator temperature, it was hot, but not to hot to hold.
Wyatt

Re: Charge house batteries with Alternator

Reply #1 – May 01, 2011, 01:01:45 pm

The previous owner of our very U320 proved this theory by burning up two alternators.

And warned me against going for three.

Even before this U320 I used the generator in the morning on our U295.

Haven't burned up an alternator yet. Not willing to experiment.

best, paul

Quote

I know that many folks on the site believe that it will wear out or overheat your alternator if you make heavy use of it.

Re: Charge house batteries with Alternator

Reply #2 – May 01, 2011, 02:15:20 pm

Quote from: P. Wyatt Sabourin – May 01, 2011, 12:48:42 pm

Paul:
...
Why run your generator in the morning when your alternator will charge your house batteries while you drive if you turn on the boost (which connects start/house batteries together)....

If your battery isolator is working properly, the alternator will charge house batteries without turning on the boost switch. The purpose of the isolator is to allow the alternator to charge ALL batteries, but keep the batteries separated when they are supplying power. The boost switch activates a solenoid that "jumps" the two output terminals on the isolator.

When you are on shore power, the converter normally charges only the house batteries. If the boost switch is on, the chassis batteries will receive charge also.

Re: Charge house batteries with Alternator

Reply #3 – May 02, 2011, 02:21:36 am

Most RVers are are hooked up to the grid in RV parks. When they travel from park to park, many of them will dry camp overnight at places like Walmart.
Not being used to relying on their batteries for power (due to being plugged in most of the time) they will run their batteries down to below 12 volts and some times much lower to 10.5 or less. The next morning they start their engine and leave Walmart.
The alternator is most likely a 130 amp unit or on those with three batteries, maybe a 160 amp unit at best.
The engine battery needs to be recharged due to starting the engine and the engine alternator was designed to do that with NO problem as it will only take a short time to restore the battery back to full charge.
However, now you are asking the alternator to do much more. In addition to charging the engine battery at 80-120 amps, you also, AT THE SAME TIME, want to charge the depleted coach batteries and they could draw in excess of 200-300 amps (if they can get it) to try to get back to a full charge. Getting them to a full charge (depends on # of batteries) could take several hours of driving. The alternator will do the best that it can but, you are asking it to do a WHOLE LOT more than it was ever designed to do. Depending on how many times or how long you exceed its capabilities, the alternator WILL finally fail. It will happen when you least expect it and at the most inconvenient time. Additionally, abuse costs money and I know that some of you have spent in excess of $1000 to get back on the road after an alternator failure. And, it is not fun to find yourself with a failed alternator and dead batteries at the side of the road when it could have been prevented.
To me it seems prudent to know as much as you can about the systems you use and the consequences of poor operating procedures.
Regards,

Re: Charge house batteries with Alternator

Reply #4 – May 02, 2011, 12:34:48 pm

Thanks Paul, for this reply (and warning).

It is hard for me to believe that a properly functioning alternator would burn up with normal use, even if heavy use. I wonder if the Leece Neville alternator are rated for less than 100% duty cycle.
I also wonder if more cooling is required because, in my motohome, the turbo charger is close to the alternator.
I also wonder if there were mitigating circumstances when these alternators burnt, for example, dirty output contacts either plus or ground which would concentrate heat at that contact point, or dirty sense voltage contact causing erratic output. I will monitor the output of, and check the temperature of, my alternator on future trips to determine a possible cause and effect.

Maybe I have been successful with running the refrigerator from the alternator because my house batteries are charged via solar and seldom less than 90% charged.

Wyatt

Quote

The previous owner of our very U320 proved this theory by burning up two alternators.

And warned me against going for three.

Even before this U320 I used the generator in the morning on our U295.

Haven't burned up an alternator yet. Not willing to experiment.

best, paul

Quote

I know that many folks on the site believe that it will wear out or overheat your alternator if you make heavy use of it.

Re: Charge house batteries with Alternator

Reply #5 – May 02, 2011, 12:53:53 pm

Right. You can run the generator until the amps requested by both banks drops to some level you are comfortable with and let the alternator take over.

Best, paul
On May 2, 2011 11:34 AM, "P. Wyatt Sabourin" <> wrote:

Quote

Thanks Paul, for this reply (and warning).

Quote

Maybe I have been successful with running the refrigerator from the alternator because my house batteries are charged via solar and seldom less than 90% charged.

Wyatt
Quote

The previous owner of our very U320 proved this theory by burning up two alternators.

And warned me against going for three.

Even before this U320 I used the generator in the morning on our U295.

Haven't burned up an alternator yet. Not willing to experiment.

best, paul

Quote

I know that many folks on the site believe that it will wear out or overheat your alternator if you make heavy use of it.

Wyatt
96 U320 40 WTFE
98 Suzuki X90 towd
Victoria, BC, Canada

Posting Information: P. Wyatt Sabourin replied to the topic 'Charge house batteries with Alternator' on the 'Foretravel Tech Talk' Board.

Re: Charge house batteries with Alternator

Reply #6 – May 02, 2011, 03:02:44 pm

Reply to JD Stevens who said:
"If your battery isolator is working properly, the alternator will charge house batteries without turning on the boost switch."

True, however, the output of the alternator will be controlled by the "Start Battery Voltage" and the start batteries will normally be fully charged in just a few minutes which results in no more than a trickle charge to the house batteries.

Turning the boost switch "ON" when driving will connect both start and house batteries together. If the house batteries are discharged and have low voltage, they will receive a high charge current from the start batteries and the control voltage to the alternator will be lower. The net result here is a much higher charge rate to the house batteries than with the boost switch "OFF".

If I want to charge my house batteries with the alternator, I start engine with boost "OFF", then turn boost "ON" and immediately check current going to house batteries. If current to house batteries is more than 200 amps, I will turn boost "OFF" for an hour of driving, then try turning boost "ON" again.
The reason I do this is that start batteries are damaged by deep discharge.

I boondock for weeks at a time and depend almost exclusively on solar with the house batteries fully charged by 2:00pm every day. I seldom require a heavy charge current to the house batteries.

If you ever boondock with me, you will be surprised at how little I use the generator, 58 hours for the last year.

Wyatt

Re: Charge house batteries with Alternator

Reply #7 – May 03, 2011, 10:42:43 am

Very interesting, Wyatt. Thanks!

But starting with the boost off is contrary to James T's recommendation.

He recommends starting with boost ON to extend the life of the starter motor.

So on one hand we extend the life of the alternator and on the other hand extend the life of the starter motor. Can we do both?

best, paul

Quote

Reply to JD Stevens who said: "If your battery isolator is working properly, the alternator will charge house batteries without turning on the boost switch."

True, however, the output of the alternator will be controlled by the "Start Battery Voltage" and the start batteries will normally be fully charged in just a few minutes which results in no more than a trickle charge to the house batteries.

Turning the boost switch "ON" when driving will connect both start and house batteries together. If the house batteries are discharged and have low voltage, they will receive a high charge current from the start batteries and the control voltage to the alternator will be lower. The net result here is a much higher charge rate to the house batteries than with the boost switch "OFF".

If I want to charge my house batteries with the alternator, I start engine with boost "OFF", then turn boost "ON" and immediately check current going to house batteries. If current to house batteries is more than 200 amps, I will turn boost "OFF" for an hour of driving, then try turning boost "ON" again. The reason I do this is that start batteries are damaged by deep discharge.

I boondock for weeks at a time and depend almost exclusively on solar with the house batteries fully charged by 2:00pm every day. I seldom require a heavy charge current to the house batteries.

If you ever boondock with me, you will be surprised at how little I use the generator, 58 hours for the last year.

Re: Charge house batteries with Alternator

Reply #8 – May 03, 2011, 01:06:48 pm

Paul,
FWIW, I have started my motorhome / coach with the boost switch on every single time I have started the engine since 1978 and I have never replaced an alternator or a starter motor. Having said that, now I'll probably have to replace them both this year.

Re: Charge house batteries with Alternator

Reply #9 – May 03, 2011, 01:09:24 pm

I agree with James T if and only if, the house batteries have sufficient charge to provide amps to the starter. This is the situation for me because my house batteries are seldom discharged more than 40 amphours and I believe that is the situation for most folks. For those few folks who have almost dead house batteries in the morning, boost "ON" will reduce the amps available to the starter.

Extending the life of the alternator is not a concern of mine because it is not particularly expensive. I am looking to purchase a spare alternator which I will carry with me.

Wyatt

Quote

Very interesting, Wyatt. Thanks!
But starting with the boost off is contrary to James T's recommendation.

He recommends starting with boost ON to extend the life of the starter motor.

So on one hand we extend the life of the alternator and on the other hand extend the life of the starter motor. Can we do both?

Re: Charge house batteries with Alternator

Reply #10 – May 03, 2011, 02:18:47 pm

Paul;
Likewise; I asked James T. about using boost on every start as that was the practice of the previous owner, and has been my practice for over 6-years. The starter loves the amperage, no harm that either of us can visualize. We also agreed it's wise to turn boost "off" as soon as the engine fires.

Re: Charge house batteries with Alternator

Reply #11 – May 03, 2011, 02:45:55 pm

Different strokes for different folks, it's your coach, do as you like. I start my engine using the chassis batteries as I would like to know that they can do that, and if I have been dry camping, I do not want to discharge the house batteries any more than they already are. My mechanical engine starts like a charm, usually on the first revolution. I have even tried not waiting for the start light to go out and it still fired right away. If I have not started the engine for a week or more, I usually disconnect the wires to the fuel shutoff and crank the engine for 15 seconds to oil the engine. This may be a waste of time as the engine will probably outlast me. I think it would take real cold weather and a weak battery to make this engine hard to start. The few electronic engines I have any experience with do not start as easily. So far no starter or alternator problems.

Re: Charge house batteries with Alternator

Reply #12 – May 03, 2011, 03:51:56 pm

Chad,
And what I do if the house batteries are in a discharged state I start the generator and let it run for 10-30 minutes. Then when I am ready to start the engine I flip the boost switch, leave the generator running and start. The hundred amps that goes into the house batteries warms those batteries (on a cold morning that can make a big difference) and is available for starting. My ISM450 fires right up, much quicker and easier than with the engine batteries alone.
Paul

Re: Charge house batteries with Alternator

Reply #13 – May 03, 2011, 04:08:19 pm

Quote from: Jerry Whiteaker – May 03, 2011, 02:45:55 pm

Different strokes for different folks, it's your coach, do as you like. I start my engine using the chassis batteries as I would like to know that they can do that, and if I have been dry camping, I do not want to discharge the house batteries any more than they already are. My mechanical engine starts like a charm, usually on the first revolution. I have even tried not waiting for the start light to go out and it still fired right away. If I have not started the engine for a week or more, I usually disconnect the wires to the fuel shutoff and crank the engine for 15 seconds to oil the engine. This may be a waste of time as the engine will probably outlast me. I think it would take real cold weather and a weak battery to make this engine hard to start. The few electronic engines I have any experience with do not start as easily. So far no starter or alternator problems.

Your ISC is much easier to start than the ISM. I had both and the difference is incredible in the start time. The ISM has a min number of revolutions that it must turn and build up heat before it will even release the fuel. It is a different process and cold weather makes it worse. I will say that I have three new start batteries and I had the ECM updated and the hard start on the ISM went away. In cold weather I too will use my boost switch too and start it with the unit plugged in or with the genset on too. Just like Paul does. It starts right up that way. I will run my generator when it is hot out for AC and when it is really cold too for power to keep the batteries up. It is simple and if you are not using much power it does nto use much fuel.

Re: Charge house batteries with Alternator

Reply #14 – May 03, 2011, 04:25:53 pm

Guess it is a good time to toss my 2 cents in. The reason the computerized engines take a little longer to start is simply due to the need for the ECM to see the oil pressure before the fuel is turned on. So it requires a few revs before the fuel get going.

One more 2 center, I always start the generator (if dry camped) in the AM to microwave my chow, make coffee and charge the battery bank. That way I feel better about not cooking the alternator, a pint of fuel for the generator seems like a bargin.
Just my view.

Re: Charge house batteries with Alternator

Reply #15 – May 03, 2011, 04:31:53 pm

John,
I think the vintage 96/97 U270 has the mechanical C8.3 320/325 engines respectively. Indeed they start on the first couple of revolutions. In addition, if the outside temps are below 60F and the engine is cold I also turn on the engine block heater to help with the oil viscocity.

Re: Charge house batteries with Alternator

Reply #16 – May 04, 2011, 12:17:14 pm

I just received some very good information in connection with the way the alternator works. According to FOT Technical, the alternator senses the voltage of the start batteries only. So, no matter how discharged the house battereis are, the alternator does not work any harder, but still charges both at the same amperage as the start batteries demand.

Great stuff...thanks James.

ps If you've tinckered with your OEM setup, or anyone else for that matter, your results may vary.

Re: Charge house batteries with Alternator

Reply #17 – May 04, 2011, 02:29:40 pm

Peter, A good point. Now if you close the boost solenoid, they should all be at the same voltage

Re: Charge house batteries with Alternator

Reply #18 – May 04, 2011, 03:22:23 pm

Quote from: Dave M – May 04, 2011, 02:29:40 pm

Peter, A good point. Now if you close the boost solenoid, they should all be at the same voltage

Eventually that seems correct. If the coach and start batteries differ in states of charge, the alternator would charge the coach batteries (via battery isolator) at the amperage rate that it senses from the start batteries. In time, the voltage would be equalized at 13.8 volts (charging) if that's the output voltage set for the alternator. I've noticed that my coach batteries will charge at 14.1 volts when the batteries are low, get to 13.8 volts for a while then drop off to 13.2 volts at times, then return to 13.8 volts [all the above readings from the Javelina and & genset running. The VDO analog dash display volt meter is not accurate/readable enough to get a good voltage reading for the start batteries while driving.]

I really need to verify the above readings with a meter (preferably with the coach not moving...

)

Re: Charge house batteries with Alternator

Reply #19 – May 04, 2011, 09:10:22 pm

Peter ,
My 1999 U295 (For Sale) has two "cigarette lighters" on the dash .The top one is attached to the house system the bottom one to the start set. I have a Walmart gaget that plugs in and shows the voltage. Much better than the gauge on the dash. Cost less than $20.

Re: Charge house batteries with Alternator

Reply #20 – May 05, 2011, 06:54:01 am

All of the above is true for a given situation.
let's talk about "burning out/up" the alternator.
Does this mean an inoperative Regulator?
Does it mean melting the stator/rotator winding?
Does it mean popping the diode's?
Does it mean bearing failure?
I installed a 10 amp circuit breaker ( non-self resetting ) in the field wire from the start batteries to the 190 amp alternator.
This done after an alternator failure where the diodes were inoperative, at the same time replacing the 17 year old "red top" Optima's.

Re: Charge house batteries with Alternator

Reply #21 – May 05, 2011, 10:43:59 am

This won't work for may of us, only owners of real vintage stuff but.....
I was dissatisfied with the diode based isolator on my old FTX as it never fully charged either battery, being about a volt short on either side. I took a Delco Remy one-wire alternator and mounted it, hooking up to the house battery and tossed the isolator. Now I have a separate alternator for each system. Vast improvement.

Re: Charge house batteries with Alternator

Reply #22 – May 05, 2011, 10:58:06 am

Quote from: Dave M – May 03, 2011, 04:25:53 pm

The reason the computerized engines take a little longer to start is simply due to the need for the ECM to see the oil pressure before the fuel is turned on.

Didn't know that but it makes sense, engine won't start without oil pressure. Makes me feel a little better about cranking the engine to get oil pressure when it hasn't run for awhile. Thinking of installing a switch in the shutoff wiring to make it easier to do. Thanks.

Re: Charge house batteries with Alternator

Reply #23 – May 05, 2011, 11:19:18 am

Leece Neville alternators are installed in millions of emergency vehicles around the world. They are designed to operate at high loads for extended periods, sometimes for days at a time. Mine is installed up high and close to the turbo where it is subjected to a lot of heat but the ECU is mounted directly on the engine and handles the heat without complaint. With a cold startup, the alternator should be asleep at full output.

In automotive use, alternator belts that are too tight are the #1 cause of failure (bearings). Most cars have alternators that exceed their designed max. rpm by a large margin. This is to insure low rpm charging in heavy stop and go traffic with the air conditioner on at full fan speed. In our vehicles, the alternator rpm should be designed to operate at it's max rpm when the engine is also at it's max. Voltage regulator (diode) failure can also be caused by a bad ground or intermittent ground. Check voltage when the alternator is at maximum output. This should be somewhere around 13.8 volts. If the alternator voltage is too high, the output will be much greater than the factory specifications and may generate more heat than the unit can tolerate.

A faulty battery could cause the alternator to charge at a higher output than designed for. Spike voltages from various sources like arc welding to the chassis could damage the alternator diodes and cause failure. Important to follow the factory disconnect list before welding. Never a bad idea to make sure the engine is well grounded.

A once a year check of the belts is always a good idea. Once you have removed the belts, spin the alternator by hand. Any kind of noise, rough spot or lateral movement indicates a bearing problem. A good motor electric shop can replace the bearings, brushes and give it a output/voltage check for less than $100. Cheap insurance. When tightening the belts, you should be able to rotate them 90 degrees without too much of a strain.

Finding a spare to carry with you is not a bad idea. A truck dismantler or Craigslist might be a good source without breaking the bank.

Pierce & Gaylie
93' U300/36

Re: Charge house batteries with Alternator

Reply #24 – May 06, 2011, 09:50:36 am

Remember that with a modern multi-rib belt you must use a belt tension gauge. Don't tighten it by feel or deflection. You'll take out the bearings.

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