Well, there are so many wise folks on this site I came here with the need for feedback. I'm trying to find a way to charge the four deep cycle batteries we use thru an inverter to power our RV. We live off the grid so our main power source is a gas generator. The other day the battery charger took a dump. Up until that time we'd run the generator for about three and a half hours and that would charge the batteries for about two and a half to three hours of power. I know the batteries are getting a little old but tonight I used the new charger we got and after a good four hours of gen power the battery bank only lasted about forty five minutes. I'll have to troubleshoot some things tomorrow but while pondering about getting a better charger I started thinking that since we run the gen that long (here's my question finally) why couldn't I just set up an electric motor/drive belt/alternator for the charging process? I do understand that batteries might not last as long this way but the savings in gas for the generator time might make up for that. And how would I set up the electrical system (in-line regulator?) Thanks for any feedback

 

How do you use your power? Do you run the gas generator while doing other things at the house, and while doing other things charge the battery bank at the same time?

When do you use the battery bank? What is it's purpose?

You could do what you propose, but you would lose some efficiency in the charging process. The motor would not be 100% efficient, and you would lose some power in the v-belts and the alternator. But it all depends on how you are using the system. If you use the generator for 4 hours each day for other purposes, and it has plenty of reserve, I guess it would not matter too much.

You do want to make sure and charge the batteries fully once in awhile for max life. I am assuming you are using the batteries at 12v and they are all in parallel?

 

What charger "took a dump"? On the generator itself?

Batteries take a LONG time to fully charge, a couple hours isn't going to do much of anything.

 

I'll try to explain our situation in a bit more detail. We live in a 31' Hitchhiker on a gold mining claim in Oregon. NO power company within ten miles. I have a 6000 watt generator used for our heavy demands but normally just use a 4000 for our needs (lights, tv, laptops, coffeemaker, microwave, etc.). While this gen. runs I've had a generic battery charger at 10amps hooked up to four deep cycles with an inverter. We don't use this while running the gen. Been running the gen. for about 3 1/2 hours and that has charged the deep cycles enough to "switch over" for about 2 1/2 to 3 hours. (We don't use the bigger draw stuff like the micro when on the battery/inverter system).
So I did a little maintence on the batteries and one was pretty low on water, topped them all out and we'll see if that helps. Also the new Shumacker charger has different settings than the old (dump) charger. I had it set for 6/2 amps and plan on testing it on the 10 amp setting but don't know if that setting has an automatic amp drop when charged. It will get sorted out I guess. But keeping in mind that every hour the gen runs costs about $1.00 and every hour the battery bank supplies our needs saves about $1.00 so you can see our battery power saves in the long run.

So, now getting back to the alternator question....I'm pondering if by not using a "battery charger" and switching to an electric motor driven alternator (I'm pretty handy at building stuff like a frame for the system) that is plugged into the generator (that is running anyhow) if that would charge the batteries faster. My theory is that we all know that it only takes a short drive to charge a low battery in a car....and a long time with a charger so treat these deep cycles like they are in a car. Make any sense?

 

A car alternator would be more aggressive at charging the batteries. You would have to do some figuring though.

Most motors are around 1800rpm or 3600rpm.

If it's a case of you already having a motor laying around, either one would probably work. But you need to figure on the horsepower needed to turn the alternator. It may turn out you will need a pretty big motor to turn the alternator, and then you would have to juggle that with the load on the generator. To use a smaller motor, you could use a pulley on the alternator twice the size of the pulley on the motor. That would reduce the load on the motor, but also reduce the alternator output.

You don't get something for nothing in this setup. Case in point, your batteries may not be exactly giving you "free" power. The generator may only cost 75 cents and hour to run if you are not charging the batteries.

They say solar panels are coming down in price. Have you looked into that to charge the batteries? I wonder what the pay-off on those would be? $3 dollars a day to charge the batteries, that's about $900 per year?

 

Chargers need to be "sized" for the battery being charged, it has nothing to do with whether it's an alternator or generator or trickle. The battery doesn't care.

But you have a HUGE battery with four "cells" in parallel. A standard 4 or 6 amp automotive charger won't cut it, (maybe as a float charge) as you've discovered. It would take day(s) to bring them up, It will work but you'll end up in the bulk and absorption stages for waaay too long and cause excessive outgassing. It's not "sized" right for efficiency or battery chemistry.

A 50 or 75 amp charger is probably closer to a "slow" rate and get things going in a reasonable amount of time, and not warp plates from excessive current. That large of a battery needs some serious juice to get back up to 100%.

Remember an alternators job is to simply recharge the energy loss from a second's worth of starting. Auto start battery application is different than what you want to do.

Heavily or completely discharged deep cycle batts wired in parallel, any "normal" alternator would get roasted in short order I reckon because it will be maxxed out for hours at a time every time. What you want to do is determine the total AH capacity of your battery bank, (not CCA) by adding up each "cell" of your bank and figure on applying no more than about 20 percent of that figure as a recharge rate. That will be a big number on a big charger.

 

As I see it there are several options here. None of them are AC motor to alternator setup though.

If just replacing the charger is the goal what you need to look into is a converter. Really another name for a charger but higher amperage and popular in the RV world. For example the one I have would likely be prefect. It's 40 Amps, controls for charge and voltage as well as a desulfation mode. Got it used for $40, kicks any typical chargers ****.

However what IMO you should do is kind of along the lines of your AC motor to alternator idea. Put together a quite small engine and an old school vehicle generator. Not alternator, generator, one off an air cooled VW would likely be cheap, common, and work well. This setup would be MUCH more efficient and could be run for very long hours at quite low fuel cost to constantly charge the batteries. This would remove the need for a charger/converter and running time on the AC generator to charge the batteries, a very inefficient method. Allowing you to only run the generator for when your running your larger AC draws during the work day.

Why a generator and not an alternator, they are much more efficient. The reason alternators are used in vehicles is that they charge better at low RPMS. But the low RPM attribute wouldn't be a need for a stand alone unit, you would set it up to run at a rather constant RPM where a DC generator is more efficient.

More I think about it the VW generator idea is pretty good. VW generators are common, cheap, parts are easy, and mechanical voltage regulators are still available(I think). Also they are pedestal mounted, they mount in an aluminum pedestal that just bolts to the block, get a stock pedestal and you cold bolt it to anything. The pulley is unique in that it is also a tensioner, the two halves of the pulley come apart and shims are placed between the two halves to adjust tension. A very good setup for a solidly mounted generator and engine. Last they are through shaft, stock one side is a pulley and the other a fan. Where the fan would mount gives you options.

The mechanical coils and points regulator could be rather handy to. If someone was clever one could be used to activate a solenoid to increase engine RPM when voltage drops.

Damn think I'll build one.

Another idea, I assume heat is an issue much of the year and at night, assuming you use propane or something for heat. Well the stock fan on the back of a VW alternator is the cooling fan for the engine. Use a VW fan shroud, likely a type 3 would work best. Use it to blow air over the air cooled engine for heat. Being careful about exhaust of course.

Some interesting reading, a member here made something along these lines for portable 12V power but using a 130A alternator. https://www.ford-trucks.com/forums/1...y-charger.html

 

Been busy now that spring has arrived around here but wanted to thank everyone for their replies. I'm going to check out the local u-pull-it places around here and look at the possible use of a vw generator.
I do have a question, do you think if running a vw gen to the battery bank it would charge the batteries to keep them up enough if pulling minimal power to the Hitchhiker? Otherwise I'm leaning towards an electric motor/gen to "charge" the bank while the 4000 gen is running. I checked out some of the higher tech "inverters" and it seems like the $40 find was a bargain. I read the thread you posted above and never knew that alternators needed (consumed) so much horsepower....that's an eyeopener. I've got at least ten various 5 to 6.5 horsepower Hondas used for gold dredges too post hole augers and would have thought that they would be "over-kill for a simple little alternator.
After a little troubleshooting I figured out what setting to use with the new charger and we now run the puppy (4000 generator) for about three hours and the batteries supply about two to two and a half hours so that's not so bad. I've also noticed that the batteries don't hold much of a charge overnite so it's time to cash in some gold dust for four new deepcycles, ha! I also will check the water level more often, enough said about that....
I have researched ALOT about solar panels (even make it yourself ones) but these dang two hundred foot doug fir trees surrounding us pretty much eliminates that idea....just not enough sun in the winter time to justify the cost.
Don't be timid about adding comments to this thread.....it's all good info., the suns shining and the bees and frogs are everywhere.

 

Given what I understand of your power usage I think absolutely. I think you could start it in the morning, let it run all day, then shut it off before you unlace your boots so you don't have to listen to it and let the batteries supply your needs at night.
I still think if you decide to charge off the 4000 gen then a converter is a better way to go.

$40 is a fantastic deal for a good inverter or converter(if that's what you meant) I was secretly jumping for joy on the inside when I bought mine. I suggest keeping an eye out on places like craigslist for people getting rid of broken trashed or whatever RVs. There are plenty of people with old trashed RVs that don't know the value of the inverter/converter.
Yeah surprised near everyone I think, myself included. Josh is a capable guy I'm confident if that's what he found to be true it is.

It makes since when you think about how an alternator works. An alternator is basically a 3 phase AC generator with a rectifier(a set of diodes) to make it output DC. Because of this half the energy is stopped by the diodes and made into heat. A 12V 130Amp alternator would take the same power to turn as a 12V 260Amp 3 phase generator.

I think one of your 5HP engines you have around could VERY easily run a VW generator though.
Solar panels have their uses but bang for the buck isn't it. For example Harbor Freight has a 45Watt kit for $138. Solar Panel Kit - Save on this 45 Watt Solar Panel Kit
Probably a good deal, and probably could get it as low as $100 with sales and coupons. But it's still just 45 Watts and that's when it has full sun. Watts is Amps times Volts. So 45W at 12.6 volts is only 3.57 Amps. So you'd need 3 of those kits to provide the same amperage as your 10 amp charger.

 

I think that would have been the way to go though if he had a sunny place to put them. They would have paid for themselves in less than a year, if he would have bought 5 of the kits. They still give you a little bit of output on a cloudy day too.

 

How much wind you got up there? So DIY kits out there, might need a couple though, but would pay for themselves in a year! Little noise, few parts, configurable, transportable? Just brainstorming....

 

On my drive today I was pondering the details of the VW generator idea I proposed.


First Amps, Watts, and HP. A stock VW generator is rated at 30 Amps peak. If that's at a high of 14V that's 420 Watts. 1HP = 746 Watts. Now Josh did this same math when he made his. But here I think it's safe to say a generator will be at least 60% efficient. If so it only takes 1HP to turn it, I'd error higher and plan on a 1.5HP minimum. Several reasons, engine inefficiency, drive system drag, and so the engine doesn't need to run at high RPMS. Of course this all changes if you leave the fan on.


Drive, my first choice I think would be bicycle parts. Chains are more efficient, parts are cheap and a wide range of ratios are readily available. This would include using a rear derailleur. Mostly because it's also a chain tensioner, however if a rear multiple sprocket setup is used it would make a change in ratio very easy. Stock I think is about 2:1 so I think that should be a minimum overdrive.


I haven't quite worked out the details of using a voltage regulator to adjust engine throttle/speed. I need to ponder the internal workings of the voltage regulator. However I'm confident a rather simple two stage setup could be setup. Two voltage regulators would be used, one setup normally to adjust the field. The second used to trigger a high speed idle solenoid off an older vehicle. One like is used to speed up the idle with AC, or on a diesel for cold start. The two stages would need to be adjusted based on how it's setup. But basically the regulator throttle setup would work in 4 stages. The first three stages all at low throttle and typical generator setup. The fourth occurs when the high setting at low throttle isn't enough to maintain voltage. This would cause the second regulator to trip on the high throttle solenoid.

 

I think the throttle setup on your homemade generator design adds too much complication. I think one steady rate of charge would be simpler and good enough.

The bicycle chain is good in theory but keeping it lubed for long life might be a problem. Since you need such little horsepower, the loss with a v-belt setup might be worth the low maintenance aspect of it.

 

You can't have a steady state of charge, it could over charge the batteries. You can have a steady engine throttle though and just use one regulator. IMO it would be less efficient though and fuel efficiency is the point.

IMO small HP numbers is a reason less drag is more important. Bicycle chains are pretty darn durable and cheaply replaced. Keep a can of tri-flo near by and give a squirt when you start it in the morning, add fuel, check oil, whatever works.

 

What might appear as no big deal when it comes to a "step down/up" system when running a gas engine for power I'll once again bring up the "off the grid" financial aspect. You guys on a "city" power grid count your blessings when it comes to power on demand...it's a whole new money consumer when running anything for power needs off the grid. This has been a "good" winter with gas under three bucks and propane at $1.65 but with all the speculation of carbon credits, etc. we here in Oregon might just see gas tax rise to the point of doubling. Just love the unexpected