Charging a 48 volt bank

[Helmar]

Hi.

I have searched but didn't find anything on the possibilities of how to charge up a 48 volt battery bank.

Right now I have a 7.5 Kolher propane powered generator that has to run 2.5 hours every 24 to 28 hours, without the sun. We have some solar but not enough.

We have a Xantrex 5.5kw and the generator is only putting in 20 amps to charge the 8 six volt trojan batteries.

I also have a bad generator head on a generator with a good running low hour engine.

It was left out in the rain....

Any ideas how to create a inexpensive gas powered battery charger?

[bob g]

in my opinion, there is no such thing as an inexpensive 48volt engine driven

battery charger, at least not a well controlled/regulated one.

it sounds like you need one that you can depend on, which precludes tossing together a bunch of junk that you have to baby sit all the time, dink with and work on continously.

then again the term "inexpensive" is somewhat subjective isn't it?

for something you can count on and not have to fuss with forever, i would expect you will be out about a grand give or take depending on how handy you are, minimum.

i am in the R&D stages of exactly what you are looking for, and so far it has cost me over 500 bucks in fried electronics.  24 volt nominal i can do as efficiently as anyone on the planet, but 48 volt nominal has so far proven to be more than twice the money and effort by a long stretch.

a thousand dollars is all the kings gold for some folks, and pocket change to others

got a ballpark number on what you expect to spend?

for kicks let run a quick tally

a good engine of say 10hp minimum, make it electric start chinese copy of a honda

400 dollars

a heavy duty alternator that can be overdriven to make 57.6 volts charging

200 dollars

a dual groove or multigroove pulley to fit the engine and alternator, w/belt(s)

125 bucks (forget the cheap aluminum pulleys, diecast, use only steel or cast iron)

a good three step controller such as a balmar, xantrex, amplepower, hehr, or something made in england or australia (depending on where you live)

300-400 bucks

misc steel to build a frame, control box for the electronics, hd rectifiers, misc electronics to make the 3 step controllers work at 48volts nominal (most are 12 or 24 volts)

100 bucks

so we are up to about 1250 bucks?  that is pretty much all new stuff

which you can trim down depending on how much you already have, how well you can scrounge and source parts and how sharp you are at making it work, or

you can custom build an alternator and drive it, and use a reostat to control charging, and have to babysit the damn thing and still probably have well over half that amount of money in it and not account for your time in custom building an alternator.

anyway that is my reality, perhaps yours and others will differ?

good luck

bob g

[zeusmorg]

 First off, you didn't tell us how big a battery bank you have.

 I suppose you want a charging option for battery maintenence?

 You could isolate and charge the batteries up in stages at 12 v. easily, that would likely be your cheapest option.

 You could also build an axial and pop it on the engine, once again, not enough details... there are plans about on how to build a 48 v, axial.

 If your batteries are constantly in a state of discharge, you have a mis-matched system. You either need more input, or a smaller bank, and use less out of it!

[Airstream]

Kohler 7.5?  Are you saying you have a 48VDC generator, or are you using a AC line unit to feed the Xantrex?

Trace/Xantrex says a true peak generator voltage equivalent to line AC is essential to proper function of chargers & many lower quality generators will not make the grade.

In order for most inverter/chargers to make their ratings they need at least 164V peak AC input; At 150V peak AC my trace 120A charger will output only 60A at 14V where a 170V peak input will allow the full 120A of charging current to flow.

[ghurd]

There is a guy working on something that is quite impressive to me.

A old 5HP B&S and car alternator with permanent magnet rotor.

It can be pull started under load, and makes a couple hundred watts at idle according to an automotive ammeter.

I guess he is not quite ready to put up a diary, but must be getting close.  It would be something to watch for.

G-

[scoraigwind]

You don't tell us the battery voltage when on charge.  How high is it getting at 20 amps?  

I am guessing the Xantrex can put out more than 20 amps (?) so what is the bottleneck?  is it the batteries can't soak up more than 20 amps (battery volts are high) or is it the engine driven genny can't kick out more than 1.5 kW or so (engine driven AC volts low)?

If the battery volts are high then you maybe need to get more batteries (reduced plate area functioning) or they are already full so you are not in need of charge just yet.  You can tell which it is by checking the individual batteries, and if they vary wildly they are in poor shape, but if they are all equally high then they are probably already charged and not ready to absorb a high charge current.

The best way to use batteries on a generator system is to keep them about half way charged on a daily basis and charge from 50 - 70% range.  Weekly or every two weeks take them up to 100% for health reasons.  (YOu can do this with your solar array instead)

Maybe you need to wait a day or two of cloudy weather before calling in the generator or you will basically be wasting fuel with it underloaded.  The battery is there to supply your house when the sun does not shine.

does this make any sense or am I away off the mark?

[Helmar]

Well, I guess there is nothing simple.

I have a good engine, 13hp if I remember right.

Was thinking of just a 48 volt alternator or something along those lines.

[Helmar]

I have 8 six volt T-105 batteries in a bank hooked up to a 5.5kw Xantrex.

The generator has the AC lines hooked up to it and the Xantrex can be set to charge ad different voltages. Default is 20 amps charge for the battery bank.

Not sure what a axial is but will go look.

Not sure what charging option is for the battery maintenance would be as I check the batteries every week.

Sorry guys, looks as I am way over my head here....

[Helmar]

Sorry, its a 7.5 Kohler 7RMY62 generator and charges the batteries via the AC lines hooked to the Xantrex inverter.

[Helmar]

Sorry, didn't know anything like that was needed.

The battery voltage on the meter shows it is about 62 volts going in at 20 amps.

The generator is doing its AC thing but only puts out 20 amps to the battery charge.

I guess the thing I though was a waste was the generator is doing all the AC stuff but only charging at 20 amps back to the batteries.

The Xantrex does all the thinking for me. It is set to not let the batteries get below 45.8 volts. Once it gets down to that, it starts the generator and charges them back up.

I have the solar panels but not tracking and peak charge back into the batteries is, I think 6.8 amps. Those are also wired up or setup to 48 volts.

When we have sunny days, the generator will only start maybe every three days as just for a run up and exercise of it.

Sorry guys, I am just a old mechanic with a few skills and can follow directions for the most part. Also a ham radio operator.

I think I just need to slink back into the shadows..

[Airstream]

Volts peak = volts RMS times 1.414

Volts RMS = volts peak times 0.7071

[ghurd]

With those batteries, 20A is about the C/10 rate.

The charger is limiting itself due to the battery voltage just as it is supposed to, at least thats my guess.

For a simple supplemental charger, right up a mechanic's alley,

http://www.fieldlines.com/story/2009/6/26/223425/021

G-

[muskeg]

  Hi guys;

 Regarding charging 48 volt battery banks using a PMA .

 My last system was 48 volts, until the inverter died.

 The next suggestions are just easy to do and worked for me.

 I tried a  the older Hornet rotor and the stock delco 12 volt coil.

 Used a chinese 4 hp honda knockoff engine.

 The unit worked actually very well. It needs about 5000 rpm from memory.

 40 amps is to much current as the coil will eventually overheat but 25 amps worked great. Use 2 units for more charging.

 Just buy the magnet rotors  and find a Delco 10si in good shape.

 A dodge  alternator works okay with a welding rheostat and some resitors to cut the field voltage down to 8 volts ., wastes power with the field.

 I tried  2 types of charge controls that worked.

 The basic one was a ASC 16 amp solar control , tapped on 12 volts of the battery bank. I adjusted the low voltage disconnect relays to kill the igniton.

What works better but is more complicated is a morninstar 60 amp charge control and their Relay Driver. A ethernet cable sends data to the relay driver for engine control. You will need a 12volt source for the relays.

 This is what I use now and reconfigured it for 24 volts.

  Please do not leave engines that do not have some sort of safety shutdowns unattended.....

Muskeg