gas power fast battery charger and inverter

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08-09-2018, 02:29 PM
DCorlando

4 Attachment(s)

gas power fast battery charger and inverter

Hi all, Harbor Freight had a sale on their small gas engines so I just had to buy one and do something cool with one.

Decided to make a heavy duty fast battery charger to charge a pair of group 31 deep cycle lead acid batteries. The batteries are then used to power a pure sine 1500 watt inverter.

The alternator used is a common automotive used on older GM cars and pickups. It puts out near max amps at 2500 RPM so I got a oversize pulley from Summit to give the small engine some leverage. Works great and the small engine has no problem pulling the load.

I get real world 80 amps charge rate at reduced engine rpm of about 2500. Or I can run the engine up to full 3600 rpm for even more.

Takes about an hour to charge the pair of batteries from about 50 percent to 95 or so. Then the engine is shut off and the inverter takes power from the batteries. The testing I have done so far has the inverter running the refrigerator, some lights and a small TV for part of the time and the refrigerator for 12 hours.

It uses a fraction of the gas a full time generator world require and the total silence when the engine is off is very nice.

Attachment 11818

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Attachment 11821
08-09-2018, 06:38 PM
kyratshooter

About 20 years ago I rigged up an old lawn mower with a similar setup.

I made a 20" plywood pulley wheel and mounted the alternator on a bracket off the discharge shoot of the mower body. Using the mower body I could roll it around to where it was needed.

I had jumper cables to hook it to whatever battery I was using, usually a 200 ap/hr deep cycle I was using to power first the RV and then the off grid home.

I had an inverter but seldom used it since I had the 12v system in the RV and liked it so well I installed a 12v system in the house as well as normal AC wiring.

That was back before all the LED bulbs and fittings were available so I am sure a 200 hour battery would last much longer now than it did back then.

I was also known to ferret out any "hot" plug on any light post in the parking lot at work and charge things up all day at school expense. I had a second deep cycle battery in the pickup as auxiliary battery and charged that up either off the engine or off the parking lot poles. I used an RV plug so I could hook up the house to the truck.
08-09-2018, 07:29 PM
crashdive123

Cool project. Nicely done.
08-10-2018, 08:12 AM
Fixit

If you will use a smaller pulley on the alternator you will get a better fuel use . Looks like your 1 to 1 right now . Been doing these for over 20 years.
08-11-2018, 11:47 AM
DCorlando

Quote:

Originally Posted by Fixit

If you will use a smaller pulley on the alternator you will get a better fuel use . Looks like your 1 to 1 right now . Been doing these for over 20 years.

The pulley on the alternator is a little larger then the one on the engine, the ratio is about .80 underdrive. For example if I crank the engine to it's full govern speed of 3600 RPM the alternator will be turning at about 2800 RPM. That puts it at it's max output of 105 amps. Normally I do not run the engine that hard, more like about 2500. At the reduced engine speed I get 80 amps (checked with an amp clamp). There are videos and pages all over the internet of people using a small pulley on the alternator and if they try to pull a heavy load on the alternator the engine bogs down. Not mine, I can hit the switch and pull 80 amps right away. BTW - it uses little fuel as it is setup now. The engine is a modern over head valve configuration and that makes it more efficient then old flat head mower engines.
08-12-2018, 10:36 AM
Fixit

Ok first don't plan on pulling 80 amps long term you will kill your alternator . A 105 amp alternator is happiest and most efficient at 52.5 amps . I normally do a 6" to 2" ratio . and run at 1500 rpm on the motor . Now I use more batteries to handlebar surge. Then the alternator will recharge them between cycles on say a compressor from your fridge . Next if that alternator fan is not the normal one you are running it backwards . Is it pulling air in the back or in the front ?
Don't mean to be critical here . Just trying to help . Spent a lot of year rebuilding dead starters and alternator s for people .
08-12-2018, 12:30 PM
DCorlando

Quote:

Originally Posted by Fixit

Ok first don't plan on pulling 80 amps long term you will kill your alternator . A 105 amp alternator is happiest and most efficient at 52.5 amps . I normally do a 6" to 2" ratio . and run at 1500 rpm on the motor . Now I use more batteries to handlebar surge. Then the alternator will recharge them between cycles on say a compressor from your fridge . Next if that alternator fan is not the normal one you are running it backwards . Is it pulling air in the back or in the front ?
Don't mean to be critical here . Just trying to help . Spent a lot of year rebuilding dead starters and alternator s for people .

The fan is the one that came with the alternator. The alternator was intended to be mounted on a car/pickup with an engine when viewed from behind the flywheel spins to the left (counter clockwise) The small engine on the other hand spins the other way so that is why I mounted it the way it is. Simple way to reverse the rotation. There is also a nut holding the pulley on and if the alternator was spun the wrong way the nut might work loose. It only takes about 5 minuets or so charging at 80 amps with the batteries at about 50 % then the batteries start to taper off. So far the alternator has been working fine but it does get hot to the touch after a run. Will keep an eye on it. Any idea of what a max temp the alternator case should be? I was thinking of getting one of those point and shoot temp meters.
08-12-2018, 04:03 PM
Fixit

The varnish on the rotor and stator is type F . It will handle 155° for an hour . My real concern was the rectifier . That being a 10si frame chances are it has 35 or 45 amp button diodes soldered on the heatsink . Will work fine if you are pulling air from back to front . Not so good if it is getting the air from the front where rotor and stator are preheating it.
The nice thing is your not back my to draw the air from a hot engine compartment to start with.
08-12-2018, 05:58 PM
DCorlando

Quote:

Originally Posted by Fixit

The varnish on the rotor and stator is type F . It will handle 155° for an hour . My real concern was the rectifier . That being a 10si frame chances are it has 35 or 45 amp button diodes soldered on the heatsink . Will work fine if you are pulling air from back to front . Not so good if it is getting the air from the front where rotor and stator are preheating it.
The nice thing is your not back my to draw the air from a hot engine compartment to start with.

155 celsius - 314F ? Underhood temps could be over 180F easy on a hot day stuck in traffic with the AC on.

When I put my hand on it after a run I would estimate it was about as hot as a tater fresh out of the microwave. 200F ???

BTW - the fan/impeller is pulling air from the back toward the pulley as it should.
08-12-2018, 09:06 PM
DCorlando

Internet search turned up type F magnet wire 155C or 314F
08-20-2018, 09:01 AM
Ralph Rotten

Quote:

Originally Posted by DCorlando

Hi all, Harbor Freight had a sale on their small gas engines so I just had to buy one and do something cool with one.

Decided to make a heavy duty fast battery charger to charge a pair of group 31 deep cycle lead acid batteries. The batteries are then used to power a pure sine 1500 watt inverter.

The alternator used is a common automotive used on older GM cars and pickups. It puts out near max amps at 2500 RPM so I got a oversize pulley from Summit to give the small engine some leverage. Works great and the small engine has no problem pulling the load.

I get real world 80 amps charge rate at reduced engine rpm of about 2500. Or I can run the engine up to full 3600 rpm for even more.

Takes about an hour to charge the pair of batteries from about 50 percent to 95 or so. Then the engine is shut off and the inverter takes power from the batteries. The testing I have done so far has the inverter running the refrigerator, some lights and a small TV for part of the time and the refrigerator for 12 hours.

It uses a fraction of the gas a full time generator world require and the total silence when the engine is off is very nice.

Attachment 11818

Attachment 11819

Attachment 11820

Attachment 11821

So essentially you built a hybrid car. :)
Looks like a pretty cool setup. You need some more batteries tho (and damn are Marine batteries expensive!)
I built a solar powered version of that getup, but mine is small enough to fit in a backpack.
I take it camping to power my laptop so I can write even when I'm sitting atop Rincon peak for 3 days.
08-20-2018, 09:18 AM
Ralph Rotten

Hah!
Found a pic of the solar power station:
https://pbs.twimg.com/media/DGeeKfoU0AEcEfr.jpg
08-28-2018, 02:32 PM
DCorlando

Update - just ran it to top off the batteries. After a 25 min run on a 90 degree day I checked the temp of the alternator and the engine and both were running much cooler then I thought. My new infrared point and shoot meter found 135F on a spot of the alternator and 125F on the lower crank case (oil) of the engine. I'm sure it will run hotter under more load but I'm thinking it may well handle more batteries.