Need ideas on limited voltage controls for antique 300 watt generator output...

[DanG]

An acquaintance has a 50-year old trailer that came with a 15VDC 20 Amp smooth & quiet running propane generator just to bulk charge batteries when remote camping. The generators only control is a mechanical timer with three hour maximum.

He's done with 90% of the trailers restoration and is testing the generator out now - but he's gone to Optima SLA batteries that call for voltage limited charging. As old as this unit is I know FLA batteries then were deemed cheap and expendable but built to withstand abuse while they lasted.

I haven't seen the unit, I don't know if its selenium rectifiers or has any filter on output, he is saying the running output is 18+ volts at the battery terminals with a nearly fully charged battery attached (no clue about ripple or any AC present) -- -- -- it was then I was asked what would a good 'module' charge module to stuff inline with the generator would be.

I can see a nice heatsinked bridge rectifier and some LC output filter applied to keep line noise down but... would a BZ solar or Tristar controller cross over to allow exact voltage settings at this toy generators full 20A output?

Any ideas?

[bob g]

i bet there is a mechanical relay style regulator to control that thing, on there someplace
and it is either stuck, purposely jambed or jumpered into being non effective.

i would look for it, and get it working properly, and adjusted to get the voltage where you want it.

is this an old delco light plant?  if so i would bet my last dollar that it has such a regulator.

batteries might have been cheap by today's standards, but they were not any cheaper relatively speaking
back in the day either.

mechanical voltage regulators came on the scene about an hour after the first generator was built

btw, i bet it is a dc generator, using a commutator and brushes, no need for rectifiers
which took a number of decades to get sorted out into something of useful and reliable size.

i would highly doubt that there are any selenium rectifiers present, and surely no silicon

bob g

[ghurd]

I do not like the idea of a MPPT regulator, if thats what you meant.
Gut feeling MPPT would result in some very expensive smoke.
G-

[DanG]

Aye, agreed - but they make fine PWM prodcts too..  It *may* be fine with new diode bridge and some filtering, the Optima charge schema includes a 15.6V max unlimited current quick-charge if temperatures are below 125°F - but this is an individual who is looking for and can afford the correct in-line 'module' with (LED readout?) precise charger - and maybe be double duty as future solar controller?

[DanG]

It's an Onan that work extremely well - excepting it requiring altitude adjustments for any change over 1000 feet.

Tecumseh LAV-30 engine on a Onan Generator Model TL-212R.

I've never seen one in person.

[ghurd]

This is probably not a great idea, but its an idea.

Power resistor in the battery charger line.  Maybe 0.5 ohm.
DT relay with the NC contacts in parallel with the resistor.
Some kind of voltage controlled switch with a wide hysteresis, like my kit set up for LVD but adjusted for a higher voltage.

Battery reaches 14.4V (whatever), voltage controlled switch energizes the relay coil, contacts open so charging current goes through the resistor, less charging current flows until the battery voltage drops considerably.
When the battery voltage goes down far enough, the relay shuts off, the charging current bypasses the resistor through the NC contacts..
As the battery voltage falls the charging current in the resistor would increase.

G-

[Rover]

This is probably not a great idea, but its an idea.

Power resistor in the battery charger line.  Maybe 0.5 ohm.
DT relay with the NC contacts in parallel with the resistor.
G-

OMG.... Ghurd suggested a relay

If money is no object , then there is potential to find controllers meant for the marine market and aux gensets.

I'm stil questioning if this is truely dc generator, or an ALT going through rectification.  I know we are very distinct about generator vs alt terms , but if you go to homedepot and buy a generator.. you are buying a power generator, the term being used loosely.

If it is a true generator, what are the possibilities of removing the generator and replacing it with an ALT, there would be a lot more choices on battery charge control

[don1]

Hey Dan G, could I throw my two cents worth in .
I think if this where my project I would look at the possibility of going old school on this one if indeed it is a DC generator.  To control the gen output by regulating the field current rather than using a dump regulator.  Bob g has a point here.  And as a replacement reg an automotive one from the early 60's  may work. If the gens  full field amps isn't to hi.  It would however be necessary to first determine if the generator is an A circuit or a B circuit so as to get the right reg.  Probably a good idea to take the gen apart and clean it and check the com and brushes anyway.

  Rover, up here in the sticks I operate an auto electric shop rebuilding alternators, generators and starters.  And where I come from if you go to home depot and buy a power generator you are indeed buying a generator. It is simply a gen that generates AC.  An alternator is a generator. But a DC gen is not an alternator. The word alternator is simply an acronym for an alternating current producing generator.
 Thats the way I done learnt it. 
    Good luck with this project and have fun.  don.

[don1]

Was looking at the close up pic and noticed the gen housing you can see the Philips headed screws that hold the fields in place I would say it is for a DC gen.

[OperaHouse]

My 1955 boat has a compound wound relay, current & voltage.  Above a certain voltage the relay closes and current flows to the battery.  If motor speed drops and current flows to the generator, the current coil of the relay cancels the voltage field magnetism causing the relay to open.  Within the generator, a current coil is wound in opposition to the field coil.  As current increases it decreases the magnetic field.  In this system there is no voltage regulation.    This might be what he has and that 18V is normal for an unloaded generator.  In my boat I replaced this relay with a diode so it would start charging the moment the generator voltage exceeded the battery voltage.

[bob g]

if you can, find an old "motors" manual from the 50's they
have an excellent section on generators and the regulators used to control them

used book stores usually have a copy and i would not expect to pay over 10 bucks for one.

as a matter of fact if money is an object, go ahead and buy one, and after you are done pm me
and i will buy it off you.  i collect old tech books and don't have a 50's motors manual for reason.

those old regulators used with the generators are so cool in that they are electro mechanical in operation
you can tweak them to do exactly what you want out of the genset with little more than a screwdriver
and maybe a pair of needle nose pliers.

there probably is a black box regualator in there somewhere, may even be a delco for all i know.
it ought to be about 3" tall, maybe 2.5" wide and about 5" long give or take a bit.

should be three terminals with screw posts if it is a delco or equivalent.  the generator output goes through
the regulator, so follow the heavy wire off the generator output and see if you can find the regulator.

it may be something as simple as it is stuck!  maybe needs nothing more than taken apart, cleaned, points touched
up with a point file (remember those), and adjusted for proper operation.

i can't imagine that there is any DC generators ever built that did not have an electromechanical regulator somewhere
in the system.  if however it turns out that it does not have one, i would study the schematics in the motors manual
and insert one into the unit. if it is an ancient unit it will need some help with the brittle/cracking/chewed on wiring anyway.

bob g