Charging systems

I built a emergancy lighting system for my house. It works good. I used a 12 volt car battery and 12 volt lights meant for droplights. What I would like to do is hook up a altanator to charge the battery. Anybody have any ideals on how to do this.:rofl: :2cents:

why don't you just buy a car battery charger?

i think the idea is to run an engine and use an extra alternator to charge the battery, although i may be wrong.

without a constant charge, i dont see a normal battery lasting too long.
of course, i'd rather keep the fridge running than a few dinky lights.

simple. Get a gas engine, put a V pully on it, and hook up an alternator.

he's running 12v house lights off a 12v car battery. for powercuts.

it just seems to me that a 12v charger is far easier and more practical than connecting it to an alternator.

Q: How do you charge a 12v battery?
A: with a 12v battery charger.

it's simple.

It may be that he wants to "re-charge" the 12 volt battery when the power is still off. Have to use the car with cables or do what UncleBob said and use a tiny gas engine. I could picture an old junk lawn mower made into a "generator" with an alternator on it.

Just get the RPMS right for the alternator.

Just get the RPMS right for the alternator.
what do you mean get the RPMs right?
an alternator will make electricity at 800 rpm.
it wont be much, but it'll do.do you mean that you have to get the RPMs to match the peak power of the alternator?

if it were me, i'd use a small engine, between 3-5 hp, and run it at idle.
then use an oversized drive pully to get the needed RPM to sustain your charge.
i'd run the engine at idle or as close to it as possible to keep the gas consumption down.remember that an alternator doesnt require a lot of power to spin, and if that is all you are using the engine to do, then 1hp or so is plenty

its more of a question of amps vs hp. The more amps you want, the more HP you'll need. optimal speed can easily be adjusted by changing the pullies, but if you don't have the power, changing the pullies will just bog the motor

many small generators have a 12V circuit BTW....but I'm not sure what price range we're talking....ie how much the OP is willing/wanting to spend on this project.

what do you mean get the RPMs right?
an alternator will make electricity at 800 rpm.
it wont be much, but it'll do.do you mean that you have to get the RPMs to match the peak power of the alternator?

if it were me, i'd use a small engine, between 3-5 hp, and run it at idle.
then use an oversized drive pully to get the needed RPM to sustain your charge.
i'd run the engine at idle or as close to it as possible to keep the gas consumption down.remember that an alternator doesnt require a lot of power to spin, and if that is all you are using the engine to do, then 1hp or so is plenty

YEs, that's what i meant. If you dont need 140A, then get a smaller alternator.

If you want to keep gas consumption down, you'd want to pick the smallest engine that would run at WOT at peak torque making enough power to turn the alternator at the required speed.

what i'm saying is that i find it extremely hard to believe that it will require more than 1.5 hp to make your standard alternator produce peak power.
your standard lawnmower engine makes 5 hp or so.
thats why i suggested running it at a lower rpm.
even though the engine will be more efficient at WOT, it will always use more gas. period.

its too much math for me to figure out right now, but if i were going to just wing it, i'd use an old lawnmower engine, and run it at around 1/2-1/4 throttle, and use gearing to get the alternator up to ideal rpms.

http://www.alternatorparts.com/how_much_horse_power_does_an_alternator_make.htm

what i'm saying is that i find it extremely hard to believe that it will require more than 1.5 hp to make your standard alternator produce peak power.
your standard lawnmower engine makes 5 hp or so.
thats why i suggested running it at a lower rpm.
even though the engine will be more efficient at WOT, it will always use more gas. period.

its too much math for me to figure out right now, but if i were going to just wing it, i'd use an old lawnmower engine, and run it at around 1/2-1/4 throttle, and use gearing to get the alternator up to ideal rpms.

http://www.alternatorparts.com/how_much_horse_power_does_an_alternator_make.htm

It generally wont, for a 100 Amp alternator. So... why not get a 1.5HP motor instead of wasting gas with the 5hp motor?

Actaully, the best device to use really would be a steam engine, but that's a bit out of the realm of this discussion. Perhaps another thread about teh awesomeness of steam engines.

the reason for using a 5 hp lawnmower engine is that it is pretty easy to find old lawnmowers laying around if you look.

i guess you could use something like a a chainsaw motor if you wanted.

a typical lawnmower revs to around 3500 rpm. half throttle would give you something like 1700 rpm, which, if you use a 4:1 pully, will be plenty of rpms for making power. standard pullys are 3:1 i think.

Yeah, all that would work fine. I'd think a 50cc motor would best though, puts out maybe 2.5 horsepower, then you dont need to inefficiently run it at part throttle ;)

Im just bustin your balls goose. The ultimate set up would be a small 2 stroke diesel turning a generator, that's if you're looking for maximum electricity from minimum fuel. But anything will work as long as its spinning the alternator fast enough. Hell, you could even hook the damn thing up to a waterwheel. Or a donkey. donkeypower all the way!

haha. my car makes 45,620,492 squirrel power

Thanks. I got a lot of imput there. Let me explain, I remember that I had a dodge truck once that had chargeing probloms. In during the day the battery stayed charged but at night when I turned on the lights the battery went dead. It drove the mechanics crazy because when they hoocked it up to the tester it tested fine. Finally when the problam was solved it turned out that the auto eletrical system sends back a little voltage feed back to the alternator and it was not doing that right. So I am assuming that hooking up alternator to battery may mean having knowledge of circuits I may not have.
So I jumped on here to get Input on the project before I started this part of it. Also In a car the alt. also uses any extra elect. to run stuff. I want to take advantage of that if posable. I have a 24' x 36' basement so I have room for as many bateries and alt. I need. It is the circuits I am not sure about. Thanks for your imput.

It may be that he wants to "re-charge" the 12 volt battery when the power is still off. Have to use the car with cables or do what UncleBob said and use a tiny gas engine. I could picture an old junk lawn mower made into a "generator" with an alternator on it.

You got it. How do I hook it up.:banghead:

what i'm saying is that i find it extremely hard to believe that it will require more than 1.5 hp to make your standard alternator produce peak power.
your standard lawnmower engine makes 5 hp or so.
thats why i suggested running it at a lower rpm.
even though the engine will be more efficient at WOT, it will always use more gas. period.

its too much math for me to figure out right now, but if i were going to just wing it, i'd use an old lawnmower engine, and run it at around 1/2-1/4 throttle, and use gearing to get the alternator up to ideal rpms.

http://www.alternatorparts.com/how_much_horse_power_does_an_alternator_make.htm

I called these guys at the link and they not only have the info and parts but the man I talked to had hooked up something simalar.:grinyes: :grinno: :p Thanks for all your help.

the regulator is switched from the ignition on all car alternators. You have to have a switch to turn it off when you're not using it.

all this talk about tiny gas engines, it really depends how much wattage you're planning on using. If you use 10KW a day, then a 50cc probably couldn't do it even if it ran 24 hours. I don't know the formula, but its a fairly straight forward one. HP = KW, there is heavy losses depending on the efficiency of the alternator, but the main point is, you can't throw a 100amp alternator on a 50cc motor. If it actually tried to apply 100 amps output, that motor would freeze solid

the regulator is switched from the ignition on all car alternators. You have to have a switch to turn it off when you're not using it.

all this talk about tiny gas engines, it really depends how much wattage you're planning on using. If you use 10KW a day, then a 50cc probably couldn't do it even if it ran 24 hours. I don't know the formula, but its a fairly straight forward one. HP = KW, there is heavy losses depending on the efficiency of the alternator, but the main point is, you can't throw a 100amp alternator on a 50cc motor. If it actually tried to apply 100 amps output, that motor would freeze solid

I dont believe that for a second. It only takes a couple of horsepower to produce 100 amps of current at 12V, or 1200 watts. Actually, using mathematical models, its ~1.3hp per 1000 watts. With losses and such, we can say it's closer to 2. 50cc motors are capable of 2 horsepower.

I dont believe that for a second. It only takes a couple of horsepower to produce 100 amps of current at 12V, or 1200 watts. Actually, using mathematical models, its ~1.3hp per 1000 watts. With losses and such, we can say it's closer to 2. 50cc motors are capable of 2 horsepower.
you are closer to right than I was (but you're not right...neener!)

this web page suggests for automotive alternators, its roughly 1hp = 25 amps in a 12v system.

http://www.pkys.com/Alternators/index.htm

So my example of a 100amp car alternator (turning at the proper RPM) it would require 4 hp

Definitely feasible with a 50cc motor

BUT....its still a question of wattage he's using total per day.

Well yeah, but this type of setup wouldnt hold up to running 100% all day. You couldnt really run your house on this, because even with a really GOOD alternator of 200 amps would provide 2400 watts of power. Most homes if you look at the electrical box the energy usage is in kilowatt-hours.

1hp per 300W? Hmm. Well sure, i have no evidence to refute this. But i'd like to do some testing on my own now to see how much it really is.

you've got to remember that he's not trying to run his house on this, he's trying to run emergency lighting.

let's say he's using 60W lightbulbs, i don't know what the average wattage is for lights designed for 12V but i'll assume 60W because that's what i use in my house. so, let's assume he's using 30 lightbulbs to light his entire house (i'm just taking these numbers from the number required to light my house), that's 1800W. 1800W = 2.34Hp. now since the alternator Uncle Bob mentioned is about 40% efficient you'll need about 5.85Hp, so if you got a 6.5Hp lawnmower (or whatever) engine you'd have enough to light 30 60W lightbulbs.

Now if you want to see how much fuel you'll need per day, you've got an engine putting out 5.85Hp (i'm using 6 for simplicity) that's 4.5kW, if you run that all day you'll be consuming ~107kWhr, which is 386,726kJ. since, according to wikipedia.org, internal combustion gasoline engines have a mechanical efficiency of about 20% (i'll assume 12% because it's a lawnmower, carburated, etc.) and since gasoline has 131,700kJ/Gal (wikipedia) you'll need about 3 gallons of gasoline to light all thirty lights for 24hrs.

sorry for the second bit, i'm trying to distract myself from studying for my linear algebra test in 3hrs.

1hp per 300W? Hmm. Well sure, i have no evidence to refute this. But i'd like to do some testing on my own now to see how much it really is.
well if you use an older alternator with an efficiency of 40% it'll take that much power to produce 300W of electrical power. I just looked up the efficiency of modern automotive alternators and at part load they're usually around 50-60% efficient (wikipedia).

i agree with all the above.

you dont need to run the entire house, just a few lights.
i'm guessing that you want a project, and are turning this into one, which is great. however, a 'real' generator will be more efficient and do a better job of integrating into your house.

since you are going the homemade way, i'd reccomend spending the extra money to get the highest efficiency alternator you can get.
also, if you have a lot of batteries, you can get away with having less output from the 'generator' assuming that the power isnt out for more than a few hours.

use heavy gauge wires and good parts, and you should have a good power source. heck, if you leave the lights off, you could probably even flip on the TV for a while.

good luck.

no matter how many batteries you have, if you consume X wattage per day, you need to be capable of putting the same wattage back into it. Extra batteries will give you more time between needing charging, but the wattage doesn't change any.

If you rarely use the system, then you can obviously get away with a smaller charger since there's more down time....but without some parameters to base calculations off of, its all rather vague.

i guess i'm assuming that he lives in a modern city that isnt plagued by frequent, random blackouts...

:wink:

I would venture to say that using DC power to run emergency lights in the house would be a major source of the inefficiency of the whole thing. Running 1800 watts at 12v that an automotive alternator puts out would be putting 150 amps through the wires (not to mention, i doubt auto alternators are built for 100% duty cycle), which is asking for a fire in anything less than heavy 00 gauge cable. It'd be much easier to run AC where you can keep the amperage low and start with a high voltage and worry aobut voltage drop across the circuit. That's why powerlines are set up that way. 400,000 volts at 50 amps. You can use nice skinny wires for miles and miles, then step down the voltage to whatever you need at the powerstations.

dont alternators put out AC in their natural state anyway?

i guess i'm assuming that he lives in a modern city that isnt plagued by frequent, random blackouts...

:wink:

I guess I'm not making so many assumptions and asking for actual data. *shrug* seems rather fair to ask, but I guess I should jump on the band wagon

well certain things can be taken for granted i guess


what about the alternators putting out AC.
i could swear that there was a rectifier or something inside an alternator to make it put out DC.