Project "Real battery charger"

Powerstroke Racer

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Couldn't think of any other place to post this, Seems like 9 out of 10 trucks that come in to get worked on have weak or dead batteries and Since you can't buy a real battery charger anymore, I have this idea of using an electric 110V motor to turn a 200 Amp alternator attached to a battery.
Generally charging a dead battery with another truck for a few minutes will allow it to start right up vs a battery charger that keeps kicking off from overheating and taking a while to charge the batteries.
So question is what hp motor to use and RPM to turn alternator.

Thoughts good or bad??
 

Dzchey21

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so your just talking about having something that will work good for jump starting vehicles?

Quick charges are pretty hard on batteries, but i understand what your saying sometimes you need to get going

I think jump starting works so well because you using the other vehicles batteries as a storage unit, i bet if you unhooked the batteries from the vehicle and relied on the alterantor only, it wouldnt work so well.

WE use napa battery chargers that have the jump start feature and it seams to work pretty well even on machines with 4 batteries that are double/tripple the size of what a typical street truck runs... so i dunno i think its a waste of time and im talking starting machines that are over 15 litres in the cold
 

Tom S

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Just for fun I think one HP equals 750 watts. 200amp times 14 volts is 2800 Watts. Divided by 750 is 3.73. Not sure if that applies real well but............ I would think a small cart with two or three good batteries and some great cables would make for a better way to go jump start a truck to pull it into the shop.
 

genuineford

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I am not sure what it is but my dad has a home built battery charger that has about a 5 hp briggs on it driving an alternator sitting in the barn. I can ask some questions about it next time I go home.
 

rsr911

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I am not sure what it is but my dad has a home built battery charger that has about a 5 hp briggs on it driving an alternator sitting in the barn. I can ask some questions about it next time I go home.

I built one of those years ago to keep my batteries charged in my old drag car between rounds. It worked pretty good but was not for jump starting, jsut quick charging. IIRC I used a GM "one wire" alternator. I put a VDO Ammeter on it. Mine was about 75-100 amps and had a 3hp Briggs. I've seen guys do this with old lawn mowers BTW, mount the alternator then put a pulley where the blade was.
 

87jumpy

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I've seen guys do this with old lawn mowers BTW, mount the alternator then put a pulley where the blade was.

That would work really slick, no more dragging around the charger in the rocks and worrying bout having enough cord.

Find ya an old clunker mower, mount ya an alternator and a couple batteries where the deck went and you could jump anything.

At work we just use the fork lift with a 200 amp alternator with really long cables to jump combines and such
 

Charles

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Just for fun I think one HP equals 750 watts. 200amp times 14 volts is 2800 Watts. Divided by 750 is 3.73. Not sure if that applies real well but............ I would think a small cart with two or three good batteries and some great cables would make for a better way to go jump start a truck to pull it into the shop.


It applies perfectly. Only disparity is energy lost to heat/sound and the rest. Your calculation is at 100% efficiency.

Regardless, it will take a substantial motor to drive that alternator. 4+hp as you showed. And at 110 volts, it would take a little over 25amps at 100% efficiency.

As far as required rpm, just look at the ratio in dia of the crank pulley to the alternator pulley on the truck and figure 1000 engine rpm before the alternator is capable of maximum amperage on these trucks and calculating the necessary alternator rpm should be a cinch.

And yes.... if this is done it should most certainly include at least one battery that stays with the alternator on a roller cart to act as a damper to the alternator, and also provide the field voltage for that alternator. Otherwise connecting the alternator straight to a dead vehicle with multiple dead batteries with no fresh battery of its own is going to load the sh*t out of it. Plus, without a battery of it's own, something like an accidental short by touching the cable ends together or similar would pop the alternator.
 

Jake

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Assume 70% for efficiency at the most. I have a 5hp gas 1800rpm engine on a 200amp alternator. I built the cart with one deep cycle battery on it and it works great. I have had thoughts of setting this up as a generator setup with a 300amp alternator and an inverter with some more batteries so while the engine is running it can start the air conditioning on the trailer and when the batteries are full shut off and run off the batteries so the generator is not running all the time.
 

Charles

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Assume 70% for efficiency at the most. I have a 5hp gas 1800rpm engine on a 200amp alternator. I built the cart with one deep cycle battery on it and it works great. I have had thoughts of setting this up as a generator setup with a 300amp alternator and an inverter with some more batteries so while the engine is running it can start the air conditioning on the trailer and when the batteries are full shut off and run off the batteries so the generator is not running all the time.


If you were only achieving 70% efficiency, then your 5hp engine would be incapable of driving your 200amp alternator to a full 200amps at 14 volts.
 

Jake

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If you were only achieving 70% efficiency, then your 5hp engine would be incapable of driving your 200amp alternator to a full 200amps at 14 volts.


yeah I know, It will not hold the full 200amp load it will bog down pretty hard at the top end. The 5hp motor cost me like $40, I had all my calcs on my crashed hard drive with some more info from denso on the efficiencies.
 

Charles

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yeah I know, It will not hold the full 200amp load it will bog down pretty hard at the top end. The 5hp motor cost me like $40, I had all my calcs on my crashed hard drive with some more info from denso on the efficiencies.


Wow. Lotta heat being generated then I take it. Is it mostly line losses to heat that's trashing 30% of the power? I imagine the mechanical efficiency in the coupling must be damn near 100. Which leaves the alternator and associated wiring to shed nearly 1.5hp. That's a lot of heat. Is this mostly losses through wire resistances?

Maybe the engine was a little weak too? Just seems like an awful lot of waste for a simple system.
 

Hotrodtractor

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Wow. Lotta heat being generated then I take it. Is it mostly line losses to heat that's trashing 30% of the power? I imagine the mechanical efficiency in the coupling must be damn near 100. Which leaves the alternator and associated wiring to shed nearly 1.5hp. That's a lot of heat. Is this mostly losses through wire resistances?

Maybe the engine was a little weak too? Just seems like an awful lot of waste for a simple system.

On a 5HP small engine - rarely does that engine produce 5HP. I had a Briggs 10Hp on a water brake once to brake it in for a race car and in stock form it put out 8HP.... Just food for thought.
 

cowboy_dan

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FWIW, charging a pair of dead batteries on a T9040 (freaking big bend-in-the-middle tractor) from another tractor, it only pulled about 80-90 amps on the jumper cables. I'm sure cranking was more, but I only got to measure current when the dead tractor was key-off. T9040 has a 12.9L engine (http://tractortestlab.unl.edu/NewH/NHTJ430.pdf).

Also of note, engine RPM on the charging tractor did not matter. It charged the same current no matter if it was low idle or maxed out.
 

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