What is the most efficient way to charge a battery with an engine?

[BioHazard]

It seems like people are always complaining about how inefficient automotive alternators are for battery charging. Is there a better way to charge batteries with an engine? I want to build a machine specifically for charging 12v batteries. I happen to have a Delco 33SI(?) 180 amp alternator meant for a heavy duty truck. Much bigger than the standard car alternator. Is there something better than this I can use to charge batteries? What about using a standard 120v gen head and high a amperage charger? Is there a ready made permanent magnet type alternator I can buy meant for battery charging that doesn't waste so much power in the field? Is there anything besides an automotive alternator that will produce a good regulated output, at variable RPMs?

The general feeling I get is "car alternators suck", so, what's the alternative? 

[Crofter]

Do a search here on     alternator efficiency    and you will get pages of info on the subject. Do another search on   battery charging    and you will get lots more posts on how to do it without frying them.

[mobile_bob]

having spent a couple hours involved with alternators and battery charging, i would like to add the following
before you get to carried away with the delco.

unless you are charging a starting battery, "and" unless the alternator has a remote sense wire
i wouldn't use the delco, because its regulator is optimized for charging a starting battery and not a set of deep
cycle batteries. also the delco regulator is buried inside the case and is not easily bypassed, although generally it can be done.

if it has a remote sense wire, that will help, but it still won't be nearly as efficient as other types of large frame alternators
where the regulator can be bypassed and control of the alternator taken over by a rather specialized 3 step controller such as
ones built by balmar, xantrex, amplepower, sterling, hehr and a few others.

as for what kills efficiency it is not the field current typically, field current for a large frame alternator amounts to only 1-2% of the
power generated at full output. some sources will go on and on about field current like it is something to be avoided at all costs, to the point
of promoting their permanent magnet field.

the problem with permanent magnet fields is there is no way to cheaply control the charge rate, most especially as the batteries approach full charge. often times a controller made to take over the pm alternators output and keep it within tight voltage limits needed by a battery approaching full charge will cost as much as a decent alternator "and" one of the aforementioned controllers together.

if it were me, i would use the prestolite/ leece neville 110-555jho alternator, and either of the controllers listed that uses a remote sense wire
and temp sensors (one on the battery for temp compensation charging, and the other for the alternator case for overheat protection).
depending on engine size if small i would recommend the balmar because it has the "amp manager" function which allows you to program
the controller to match the engine's output to the alternators need for mechanical power input.

the 110-555 will set you back maybe 175 bucks (usd), the balmar mc612 controller will fetch about 250 on ebay if you watch for one, and the
xantrex can be had for around 200, but be sure to get the one with remote sense capability, not all controllers have this capability.
the sensors average about 30 bucks each.

for about 430-480 bucks you can get enough stuff to have a quality 3 step charger, that will be about as efficient as you can get in my opinion.
while this may seem a bit pricey to some, if you are buying fuel to drive the system it won't take long to recover the investment.

btw, the 110-555jho is rated at 160amps, but figure on about 120amps max hot for continuous use and it will be a happy camper.

bob g

[veggie]

Perhaps one of the biggest problems when charging a battery bank with an engine is the "float" charge.
Once the bulk charging is complete, the engine must run for a long time virtually unloaded to complete the float charge.
For some systems, this can be a big waste of fuel and a drag on the overall system efficiency.
One thing I am considering is to stop the engine after the bulk charge and let a solar panel to the rest.
If you have a CHP system, the generator can be put to work driving a heating element (load dump) during the float phase so that the waste energy is captured.
Something to consider as you set up your charging system.

cheers,
veggie

[BioHazard]

Thanks for the info guys! So it's not really the alternator itself that's inefficient, it's just the regulator? I really like the sound of that Balmar controller, can that not be made to work with my Delco alternator? My alt has been burried in a box somewhere for so long I forgot exactly what model it is, but I have a service manual for it somewhere too. It doesn't have any sense wires but I think some versions came that way from the factory and maybe mine could be converted?

Just out of curiosity, has anyone ever done any cooling mods to an alternator?

What I'm doing is building a bit of an inverter-generator, I have a Xantrex 3kw inverter and an electric start Briggs engine, there will also be one or two batteries for big surge loads and small loads without the engine running. I'm working on a controller to autmatically start/stop the engine to charge the battery.

[mobile_bob]

i am going to probably piss off somebody but here goes,

probably the best that alternator is going to be is something on the order of 60% efficient at its peak

now delco recently has been working on and has released some reportedly high efficiency units, some iirc over70%
efficient.

in my opinion its 12volts that is the problem, its just hard to get much over 70% at that voltage level with an off the shelf
unit, because it is built to be a broad spectrum machine capable of charge from engine idle to cruise speed.
in order to achieve this certain compromises have to be made.

you might be better with an 80% efficient AC head, driving a high efficiency charger plugged into it, 75% overall efficiency
should be attainable and you get AC from the genhead to boot.

its not until you get up to 24 or 48volt nominal that the efficiency can be improved significantly.

all depends on what you want to do, and what compromises you are willing to live with.

it would appear that because you are using a gasoline engine, maximum efficiency is probably a secondary concern
and reliability/simplicity along with a learning experience is probably of primary concern?

if that is the case, i would simply open up the delco and change out the regulator for one that has the remote sense line, and
give that a whirl. no real reason to go with an expensive controller while you are working out the rest of the system, it can be added
later if you like. the advantage to an oem regulator with sense line is it has an embedded temp sensor which will cut back the charge
rate if the alternator gets too hot, which makes the price of the regulator about the same as a temp sensor for a balmar.

bob g

[BioHazard]

it would appear that because you are using a gasoline engine, maximum efficiency is probably a secondary concern and reliability/simplicity along with a learning experience is probably of primary concern?

You could say that. I've been building this 'thing' for years, before the "chinese engine revolution", and the matching cheap generators. The main thing I wanted was a generator that could vary the RPM based on load, like the Honda inverter generators. I modified the engine extensively with go-kart parts, so I could have useable power from about 2000 to 4500 RPMs and was able to use a smaller displacement engine. (forged stroker crank, increased CR, billet aluminum rod, special cam, etc)

Now, I'd probably be way ahead just going to harbor freight and getting a 3kw generator for about $299. But, I've got all these peices to put together, I'm thinking a 12 volt generator might be a useful thing to have, regardless of efficiency. One thing I'm particularly interested in is using this generator in my boat to power a trolling motor when the main motor goes down. (antique outboards can be a bit picky) As it is now I won't leave shore without an extra battery for jumpstarting...

Mostly I'm looking for "amp efficiency", rather than fuel efficiency, that is, the most electricity I can get for the horsepower the small engine has. (probably around 8hp or so peak)

Something I never thought about before that I am now is that the Honda inverter generators probably generate variable input voltage based on load for the inverter, sort of like a wind turbine, right? This is the key to the whole system, I HATE any equipment that runs at 3600RPM constant no matter the load...

[BioHazard]

How about I ask this way:

The general rule of thumb for generators is 500 watts per engine horsepower, right? (2hp per kilowatt) A 6hp engine should easily make 3kw. Now, using a truck alternator instead of a regular gen head, how many watts can a person expect per horsepower?

[mobile_bob]

usually they figure about 25 amps per hp for a 12volt system, but i think that is overly optimistic for a typical 6hp gas engine
wherein it is my belief that they are 6hp peak rated and not 6hp continuous

125amps max continuous ought to be attainable, unless you are at a high altitude, that being with the engine running at full rated rpm
which is likely 3600rpm and the alternator belted to run at around the same. so basically a 1:1 ratio ought to be about right.

to be sure we need to know which delco you have specifically, and look up its performance chart, to see at what rpm it makes 125amps
"hot" rated.

if at 3600rpm it makes the 125amps hot, then one to one is where you ought to be in my opinion

be sure to use dual A belts that are notched, such as the AX series and use a castiron drive pulley. don't even think about aluminum
if you can fit up for a 5-6 groove microgroove belt that would be ok too, provided you use a tensioner of somesort.

i thnk that will get you pretty close.

such a setup should provide for the 125amps at full output although screaming at 3600rpm, it needs to be running there for adequate power
and cooling for both the engine and alternator, however after the battery gets to about 80% state of charge you could reduce the engine rpm
to something around 2500rpm because the amperage needed generally is quite low, and the power required of the motor is also low.

bob g

[BioHazard]

Are dual belts really necessary for something this small? I already got a big cast iron (single) pulley for the engine but haven't got one for the alt yet. I want the belt ratio to be so that the alt is turning at it's maximum speed when the engine is at 4500RPM, (yeah, I know that's faster than 'spec') and then somewhere close to 50 amps at a high idle speed.

The engine started life as a 190cc 5.5hp, but later modified with Briggs 206cc and 7hp parts, and then some. Go kart racers get upwards of 15+ HP out of these little things at about twice the RPMs I'm running.

Part of my reasoning for the "souped up" engine is that it was lighter weight than one rated for more HP - but after I start adding truck alternators, batteries, inverters, and a metal cart for it...it's not so light anymore.

[mobile_bob]

a single A groove belt is only good for about 75amps continuous, a B section perhaps 100amps

that is for an AX and BX belt

you likely will be better off with a serpentine belt, it will be lighter and can handle much higher power transfer levels
per unit weight.

bob g

[Crofter]

Biohazard isn't there a contradiction in looking for the most efficient alternator, then turning your engine at 4500 rpm? Any experience I have with dragging extra output from an engine via rpm hurts efficiency, and longevity goes for a crap. If getting the most output from the smallest package for short period of time, then I can see the rationale.

[BioHazard]

you likely will be better off with a serpentine belt, it will be lighter and can handle much higher power transfer levels
per unit weight.

bob g

I guess the question is...where can I find a heavy serpentine pulley, that fits on my 3/4" engine shaft?

Biohazard isn't there a contradiction in looking for the most efficient alternator, then turning your engine at 4500 rpm?

I believe with a gas engine, properly built to run at high speeds, small displacement and high RPMs gives better fuel economy at the cost of engine life. I'm pretty sure this is how the Honda inverter generators work. Don't get me wrong, I didn't just tweak the governor, it has a completely different cam, intake and exhaust system than Briggs gave it. The main objective here was to start a large surge load with a small engine - I can get 6kw from my inverter, something a 5.5hp engine/gen head could never do. This is enough to run my house if I need to (mostly natural gas) and, another thought was that in an emergency, if the engine dies, all I need is a car and some jumper cables and I'm back in business.

That said, my power hasn't so much as flickerd in the last 10 years...the jerks at the power company went and bought power from six different sources and burried all the power lines...it never goes out, they ruined all my fun!

[BioHazard]

Just out of curiosity, can anyone tell me what the mechanical efficiency is for V belts vs Serp belts vs direct drive?

Also - Bob - you say it's 12 volts that's inefficient - if I did the exact same thing, with a 24v regulator instead of 12v, would the overall efficiency be better? I do want to use two batteries anyway...

I may just end up mounting this alternator and inverter in my old Chevy truck, it has the factory "high output" 63 amp alternator complete with a heavy duty 10 gauge factory output wire. LOL!

[mobile_bob]

as near as i can tell a good drive using quality components, properly engineered will return about
96-97% efficiency for a V drive, and the microgroove will do about 98% if the same considerations are met.

poor quality parits, no concern for following the manufactures engineering and all bets are off, a V drive
can be horribly inefficient if not done properly.

if you control the field as described in my white paper, and run the alternator at 24volts nominal, it will improve the
alternators efficiency at similar power levels.

bob g