Another problem with these old ferroresonant chargers is they keep charging
your batteries until they are cooked as they don't cut back enough.
I would suggest checking marine stores before spending hard earned dollars
to buy outdated ferroresonant converters.
The boating industry threw them overboard awhile back and went to greatly
improved chargers which have a three modes of charging. They quickly charge
your battery until about 90% charged, then switch to a conventional charger
until 100 percent charged, then enter a float mode to supply no more than is
needed to keep them charged. This greatly extends battery life.
Some of the larger 120v inverters include this type of microprocessor
controlled charger when on shore power. One of them has a nice feature that
monitors total shore power current and automatically reduces the battery
charging current to keep from overloading shore power circuits while you use
other appliances.
Don
- -----Original Message-----
From: Dick Kennedy
Date: Tuesday, August 04, 1998 14:02
Subject: Re: GMC: Converter recommendations?
>Ralph,
>
>Those old power supplies use what is called ferroresonant technology. I've
had to repair mine twice in the past year. Most recently when the starter
>bracket broke off the generator while the generator was running it burned
>the terminals off the coach battery and also blew the comvertor. I don't
>know if it was the short itself or the transient that caused the problem.
>
>Inside the convertor there's a huge transformer, a rectifier, and some big
>AC capacitors. These capacitors resonate with the transformer winding and
>are the basis for the voltage regulation. Mine is a Triad unit and it had a
>pair of 4 uf 650vac caps connected in parallel inside. Last fall one of
>these caps was shorted and last week I replaced the other one. I had
>difficulty locating the 4u caps and when I finally did they were very
>expensive so I repaced each of them with a pair of 7.5 u @ 370vac caps in
>series. It now works just fine and is now back inside humming away. So
yours
>is probably repairable if you can find someone to do it at a reasonable
price.
>
>The problem with these old beasts besides the amount of iron in them is
that
>they draw a lot of standby power. If my memory is correct mine drew about
70
>or 80 watts standby with no load. This is enough to make the transformer
run
>hot and is more power than I want to leave plugged in full time when the
>unit is parked at home. I then retrieved a similar unit from an RV that I
>had sold to a friend. It's stand by power was pretty much the same. My GMC
>is a '75 and the other RV was a '79 and the two supplies were very similar
>but not exactly identical.
>
>As the next step in this saga I obtained a more modern supply from an rv
>surplus place.
>The modern units are wired differently. On the GMC the coach battery is on
>line all the time and the supply keeps it charged. On the newer stuff when
>on AC the battery is switched off line and is trickle charged while raw
>rectified AC is fed to the coach itself. The problem with this system is
>that many solid state items won't work from unfiltered DC. I assume that
>newer RV's must route both raw power for lights and battery for the critcal
>things. This is probably technically a better system since there would be
>less cycling of the batteries. I didn't want to get into making changes so
>I returned that supply to the dealer.
>
>In this same time frame I was getting back into ham radio after being out
>for 30 years. I purchased an Astron RS-35 (
http://www.astroncorp.com)
supply
>for use with the ham gear. This supply is regulated and filtered at 13.8v.
>It would be a candidate for a replacement unit but since it's not designed
>for use as a battery charger I would assume that it would drain the battery
>when unplugged. Astron also sells a line of switching supplies that are
much
>smaller and presumably more effecient. Last fall I sent an email to Astron
>asking some specifics for our application but they never responded.
>
>This is as far as I took my search. I solved the standby problem by leaving
>it unplugged when I'm at home. These newer designs are smaller and more
>effecient than the old ferroresonant guys but I didn't really find anything
>that fit exactly what I needed so I stayed with the original. It would also
>be nice to have a quick charge mode built in.
>
>These Astron supplies are available used for under a $100 so if my supply
>failed today I would probably put the Astron in the RV and use a high
blower
>relay for isolation if necessary. From the postings there are other
>alternatives also but I don't know the relative costs.
>
>Hope these ramblings help someone.
>
>Dick
>
>
>>Noticed that my converter -- looks to be original -- doesn't always want
to
>>work even though it hums up a storm. Any recommendations about which
models I
>>should check out? What are some of the differences that more experienced
folks
>>have found and what sources do you recommend?
>>
>>Thanks for the advice.
>>
>>Ralph Edelbach, '74 Glacier (still being gone through!)
>>
>>
>>
>
