Running the bank charger via an inverter

[microage97]

Hello All,

Will I be able to run a battery charger via a power inverter? I am putting together a household back up batter bank that will me maintained via house hold current, but when the power fails I am wounding if I can power the battery charger via a lawn mower engine and alternator hooked up to a battery and power inverter. I already have this built.

Dave

[Flux]

That's about as clear as mud, you had better try to explain it properly.

What sort of alternator have you hooked to an engine?  If it is a mains voltage/mains frequency alternator then yes you can use it to drive a battery charger, but the performance will depend so much on the alternator and in some cases it may be poor.

If it not a mains voltage alternator you are probably going round in circles with batteries and inverters and chargers. You need to hit it one go if possible with something attached to the engine to charge the battery you are relying on. Umpteen stages of power conversion will probably get you near nothing at the end of several conversions.

Flux

[microage97]

Thanks Flux,

Sorry for not being clear. Ok here is what I am trying to do. I am setting up a 500ah battery bank that will power my refrigerator and freezer (120V) if I loose power at the house. This will be done in a manually fashion as I will have to unplug those appliances from the house power outlet and plug them into the battery bank outlet that is hooked up to a 2300 watt inverter powered from the bank. The fridge uses about 1200 watts a day or there abouts on average. I may need a larger bank as I realize this is really going to draw on the bank.

I am want to power the bank charger via the house power when it is working, but if I loose power and I am powering the refrigerator and freezer I am going to need to charge the bank, can I use my 12V 65A car alternator powered by a small engine to run another power inverter to power the charger to recharge the bank? I figure that I would shut off the appliances while I am recharging to speed the process. I understand that this may not be the best set up, but it is for emergences and what not.

Dave

If you need more specifics, please let me know.

[Flux]

You don't give the voltage of the 500Ah battery bank that you want to charge. Without that it is almost impossible to help.

A battery charger run from an inverter is not likely to work very well unless it is a first class inverter and the battery charger has electronic power factor correction.

A cheap MSW inverter and standard car battery charger would be dreadfully poor and even for emergencies would be abysmal.

Unless the main battery is above 48v you would do better to make the alternator charge the battery directly and remove the inverter/battery charger link.

Flux

[microage97]

Ok thanks Flux.

It is a 12V bank.

Dave

[Flux]

Simple, just use the alternator direct to charge the main bank instead of the intermediate battery and get rid of all the losses.

Flux

[microage97]

thanks for your help, flux. Will I need to get rid of the voltage regulator and use a rheostat to control voltage? I am just wondering as I came across a web page describing this.

Dave

[Flux]

Normally that is a good idea when you are looking to charge a battery quickly as the regulator tapers the charge off to early.

In your case it will almost certainly be better to leave the regulator as it will hold the volts from tripping your inverter. The battery will drop to below regulating volts in a few seconds of use and if the engine and alternator are capable they will balance the inverter current. If you bring the engine in late after the thing has been supplying load for some time the alternator will go flat out ( or as near as the engine can manage) and get the thing up to float volts quickly. The mains charger will do the final stage of charging when grid power comes back.

The only thing to watch is the gear ratio between the engine and alternator, if you drive the alternator too fast then when it goes flat out it may stall the engine. If you can't easily alter the ratio then you could add a little resistance in the field circuit but still leave the regulator. The regulator will then look after volts but the series resistance will act as a current limit.

You will have to dive into the alternator and unless you are familiar with the things you may struggle to find where to add the resistor. Far easier to select the pulleys so that the engine can always manage the alternator when the regulator demands full field, then you can use the throttle to reduce current if necessary.

Flux

[microage97]

Thanks Flux for your help! I built the "gen set" following this site: http://theepicenter.com/tow082099.html

[microage97]

Hopefully I won't have a ratio issue between the motor and the alternator. I followed the site howto below and this guy recommends a certain sized pulley that I went will, so we will see how it goes before I really need it.

Dave

[Waterlogged]

I built a generator like that that I still use. My first build had the Honda GX140 5HP motor and a 12 Volt Delcotron 63 amp alternator next to each other with a belt. This combination ran the alternator backwards, and it overheated. Next, I bought the direct drive brackets and the Lovejoy couplings, from The Epicenter.com. I had to replace the rubber cross once, because it wasn't straight and it wore out. Since then, I keep a spare on the shelf, because two are cheaper than the fuel to get one. With one on the shelf, I haven't had to replace it for two years. It is used for about 4 hours a day, a couple of days a week. I made no alterations to the alternator, other than replacing the pulley with a coupling half.

Rod.

[microage97]

Good to hear that you have had success with this setup. Did you do anything with the exhaust to quite things down?

Dave

[Waterlogged]

Yes. I pointed the exhaust away from my camper. With the direct drive, it can also be idled down after bulk charging is done. I usually use a clamp meter to read the charging current, and idle it down until it can just maintain that current. It still outputs about 15Amps at about 1800 RPM(idle). Sometimes it self excites, for the other times, I have a momentary contact push button switch between the small wires that plug in the back. The larger of the two wires in the plug goes directly to the (+) output to sense system volts. This wire can alternately be wired to a main distribution point to sense the voltage in the system as opposed to alternator terminal voltage. The smallest wire is normally wired through the idiot light on the dashboard. When a car is started, power is sent through the light to excite the alternator. Once the alternator is working, power is no longer required from this circuit, (it supplies what it needs) and the light goes out. The light is not necessary unless you want the indication.

Rod.

[americanreman]

I can understand why you want to do this because I've been there before...you already have a charging system and - or it's not easy for you to run dc wiring to the bank from the alternator (maybe too far away). I experimented with a walmart deep cycle hooked to a 700 watt inverter and ran a charger from that and kept the deep cycle charged with the alternator, it worked pretty well but you have to get the right charger that is happy with the waveform. You are much better off hooking the alt to the bank.

I've tried alot of different pulley combinations, 1:1 works best for me (same as direct coupling). You can run it about 1200 rpm and get good power from it without all the noise, vibration and wear and tear.

You should build a simple op-amp state of charge monitor that kicks on a relay to kill the gas engine before voltage raises to over voltage inverter shutoff, forget about the regulators and control the field manually.

Good luck, it's a fun project that works very well, today's engines use alot less fuel. My first one (1981) was a briggs 3.5 horse with a Ford 35 amp at a remote cabin in northern Michigan, used alot of gas. I now have a few honda 5 horses that use little fuel and are pretty quiet at around 1200 rpm.

[microage97]

Thanks Americanreman. I am going to do some experiments to see how much the alt will be able to keep the bank chargered without too much work. I understand that it won't he 100% fully charged, but maybe I can keep it over 80%.

Dave

[ghurd]

I have done it a few times for unusual situations.  It works.

Like charging 24V batteries from a 12V solar system.  400W Vector cheapie inverter into a decent 24V transformer based battery charger.  It's been running maybe 8 years. No problems except horrid efficiency, but it keeps up fine.

I wouldn't try it with a 'smart charger' style battery charger.

If both batteries are 12V, there is no need to have the extra step.

If both batteries are 24V, get a 24V 'one wire' alternator.

Efficiency will be better if the loads are left on while the motor is running.

G-

[microage97]

Well I gave running the alternator to charge a single deep cycle batter a try. I ran a MSW 1000 watt inverter and a halogen work light as a load of about 360 watts. Wow the alternator was running full out and got really hot dumping out full power.

I guess I need a rheostat to control the field, and and amps out put.

Dave

[ghurd]

Is the 500AH battery bank 12V?  Is the 2300W inverter 12V?

Be sure the alternator is turning in the proper direction or the fan won't work.  I recall hearing of some that overheated and failed when turning the wrong direction.

I know a guy who made a couple.  He used a long wire to the battery to slow the amp output.  The voltage drop in the wire tricked the alternator into making less amps.

I don't know, maybe 6 or 8' each of #8 wire?

The wire did get warm.

Have you seen The Epicenter?

http://theepicenter.com/tow082099.html

G-

[microage97]

I have seen the epicenter and that is where I got the mounting plate. I am pretty sure it is spinning the right way, at least it was putting out the correct voltage. It got supper hot though after a heavy load was put on the battery. I haven't tried it on on the bank yet.

Dave