Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 16, 2025 ...

Auto Gen Start / Diodes / Voltage

September 18, 2013, 09:58:52 pm

Somewhere I remember reading about installing a diode in order to change the voltage at which the Auto Gen Start will start the generator.  I think, it was the AGS used in 1997, which I was reading about.  Now of course I can't find it.

Does anyone know if this is possible?  Could someone explain (in very simple terms) how you might go about doing this?

Any info is greatly appreciated.

I know I could install a stand alone AGS, but I would really like to trick the current one into working better.

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Re: Auto Gen Start / Diodes / Voltage

Reply #1 – September 18, 2013, 10:50:38 pm

Magnum generator autostart add-on

I put in a Magnum AGS, also. When I consulted the help line, the expert highly recommend leaving the diodes out. His reasoning was that with any load on the battery, the 12V setting on the AGS will start the generator before it is discharged too far. IIRC tables for 12V battery show an unloaded battery at 12.2V is at about 50% discharge. Any load will drop the voltage lower that 12.2V.

We have used the AGS very little, so I don't have the experience to recommend for or against using the diodes.

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Re: Auto Gen Start / Diodes / Voltage

Reply #2 – September 19, 2013, 09:36:02 am

THere was a black box in my dash that controlled the genset. I used a multimeter and turned a screw and it adjusted the voltage for auto start.  You have a different year so I do not know if it is the same.

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Re: Auto Gen Start / Diodes / Voltage

Reply #3 – September 19, 2013, 02:01:37 pm

We installed the diode as mentioned in J D's reply. We would rather have our gen auto-start do its thing when battery voltage gets down to about 12.2 and avoid deep discharges. Our auto-start has been helpful, to notify us when we connect to shore power and forget to turn pedestal breaker on, or when on solar and the sun is not keeping up. When dry camping we usually turn auto-start off at night, but we do turn off all unnecessary loads with multiple power strips, allowing our electric refrigerator to have full use of house batteries.

If the existing generator autostart voltage setting does not adjust low enough, find the voltage sense wire, disconnect it and putting a common diode in-line would allow the adjustment to use a higher voltage range. Diodes are a simple way to reduce DC voltages without consuming (amperage) power. With auto start turn-on voltage range of 11 to 12 volts, adding a diode can change the range to be approximately 11.5 to 12.5 by fooling the controller into thinking the battery voltage is about 1/2 volt lower than it really is.

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Reply #4 – September 19, 2013, 02:15:19 pm

Thanks everyone, that was exactly the information I needed!!!!


Now I have some experimenting to do.

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Re: Auto Gen Start / Diodes / Voltage

Reply #5 – September 19, 2013, 09:51:14 pm

Barry's suggestion of adding the diode will indeed shift the adjustment range on the AGS by about 0.5V, and will provide a more conservative starting voltage for the autostart function.

We normally turn "Boost" "On" to start. If AGS autostart is "On," the voltage drop during starting is likely trip the autostart and the generator will fire up. Surprise! Offered FWIW.

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Re: Auto Gen Start / Diodes / Voltage

Reply #6 – September 19, 2013, 10:07:14 pm

Installing a diode sounds like a good idea and I think i'll play around with and see what works.

But as I was driving today, I started thinking....  if the diode drops the voltage, will the generator shut off??? 

Could dropping the the voltage .5 volts be enough that the AGS never see the batteries as full, therefore the generator never shuts off automatically?  Seems like this could be a possibility. 

According to the Foretravel owners manual:  The Power Technologies AutoStart System will start the generator at approximate 12.2 vdc.  Charge the batteries and shut off the system at approximately 14 vdc.  With a diode installed that would change to approximately 12.7 vdc and 14.5 vdc.  Will it ever see 14.5 volts to shut off?

I don't think it would be a problem with the Magnum AGS which shuts down after an amount of time. 

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Re: Auto Gen Start / Diodes / Voltage

Reply #7 – September 19, 2013, 10:16:41 pm

Hi,

What is the best way to test the autostart function?  Our pre purchase inspection said that the autostart function was not working.  I wrote and asked how they tested it but I never heard back.  Generator hours were 161 when we bought it.

Thanks,

Roger

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Re: Auto Gen Start / Diodes / Voltage

Reply #8 – September 19, 2013, 10:22:35 pm

Magnum AGS charges for a set amount of time. Its autostart voltage range is adjustable from 10 to 12 volts. Adding one diode changes the range to about 10.5 to 12.5 volts, which is more conservative and more appropriate for use in a FT.

Your description implies that a diode in the sense line would not be appropriate for the PT Autostart.

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Reply #9 – September 20, 2013, 01:00:57 pm

Roger,

I would test the AutoStart by starting the microwave with the AutoStart switch ON(not connected to shore power of course).  That should drop the coach battery voltage very quickly.

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Re: Auto Gen Start / Diodes / Voltage

Reply #10 – September 20, 2013, 08:18:35 pm

Thanks, Brett,  I'll give that a try.

Roger

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Re: Auto Gen Start / Diodes / Voltage

Reply #11 – September 22, 2013, 12:50:09 pm

Is there concern w/charging voltage? 

I noticed my charger is not rated with the house battery manf. recommendation.  In which case the batteries never fully charge which contributes to new batteries (UGH). 

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Re: Auto Gen Start / Diodes / Voltage

Reply #12 – September 22, 2013, 05:10:57 pm

I think that any charger setting will eventually get batteries fully charged. If voltage setting is too low, it will take longer than if voltage is correctly set. If voltage setting is too high, battery may gas, which will damage a sealed battery. I don't know what contributes to needing new batteries. Maybe turning off charger for a few hours will give batteries a rest and a cause the charger to go back into charging mode from float.

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