How many amps can I pull?

[Derb]

Hi Fellas. I nearly pissed myself laughing when i started reading this thread. Have you not ever noticed when in your 6 or 8 cylinder car of around 180 HP the engine rev's die off a little when you turn on your headlamps? 2 x 60 watts plus maybe another 20 watts for tailamps etc. 140w/13.6v = about 10.5 amps. Your 2.5 HP aint draught horse power, that motor is going to have a hernia trying to poke out any more than 30 amps continuous. Now a lister 2 HP may be good for a few more amps but not your off the shelf hondaroid or similar. Good luck Boss.

[Henry W]

Hi Derb,

As long as Hp and Torque specs on an engine are true it will put out. It does not matter what brand engine your running. Now if the specs are over or under rated from a specifec engine manufacture  than this is where a problem would manifest with calculations. We cannot assume that off the shelf hondaroid or similar engines will not put out unless the engine is ran on a Dynamometer or a DC charger built and ran under loads.

Henry

[BioHazard]

Have you not ever noticed when in your 6 or 8 cylinder car of around 180 HP the engine rev's die off a little when you turn on your headlamps?

My cars don't do that...sounds like you may have a problem with your battery....

Your 2.5 HP aint draught horse power, that motor is going to have a hernia trying to poke out any more than 30 amps continuous.

I know for a fact this little 80cc motor can make a lot more than 30 amps CONTINUOUS...it's just a matter of finding the best gen head to do it. (a car alternator isn't it)

Here's the same engine putting out 60 amps with something other than a car alternator:
http://www.yang-ke.com/cpshow.asp?proid=20091026135608

[Derb]

Hi Boss. Yup - your little 80cc engine will most likely do the business for a little while. My point is that it will be maxxed out whilst doing it. A Bamford or Anderson or Lister 2 HP unit will do it 24/7 year after year without breaking a sweat. Dumps around the world are full of chinese clone engines which simply don't last. Gotta be a few good ones amongst them but you can't beat the genuine article for the long haul - particularly if you are going to be giving them a bit of a hiding. cheers.

[BioHazard]

Not everything needs to weigh 1000 pounds and last forever and cost a mint.....

We're talking about a machine I would be thrilled to get 500 hours from, at an engine cost of $79. And it's portable.

[Derb]

Hi Boss. That being the case, try the fisher and Paykel PM type generator. Free from the tip. Heaps of info on google. I have just finished one and its a doddle to do. You would just have to use a simple belt reduction drive. Cheers.

[wiebe]

Bio .
Just take de alt and motor and have fun .
My 120cc honda 4,5 hp ,has a 55 amps alt and has got used a couple of time,s now.
If de engine cant take a big load just put thinner wire,s on the alt to prevent the gen from drawing to much amps.

Not a nice regulation but is works .

But i have not met a empty car batt that would like charge more then 30 amps .

Greetings wiebe.

[getterdone]

in my early days or experimenting with a 5 hp motor driving a alternator. i used different resistors to make my alternator behave. i don't remember what values they were. i even used a variable resistor until it burned up. when the batt's were low i had a switch that switched between the different resistors. this allowed the engine to be happy at max output depending upon batt. state of charge.
doing it this way, your 2.5 hp engine will be happy.
one more thing., once your batt's are close to being full your engine can be throttled back.
you will have to use an alternator that uses an external voltage regulator and get inside the thing and disable the regulator and hook up your resistors. 
i hope this will help.

[Mad_Labs]

I have a 5.5hp Honda hooked up to a 90 amp alt via a single A belt. I can pull 50 amps continous, anything more gets the engine too hot. I can pull about 65 amps for a short burst. I use a larger pully on the engine and a smaller one on the alt to up the RPM's a little, I forget the ratio. I made my own field coil controller, works great and was easy to build, I can equalize as well. I have been using this setup for 2 years or so. I live off grid and run the poor thing for hours in the winter. I'd expect 25-30 amps continous out of your motor.

Jonathan

[injin man]

I have a 5.5hp Honda hooked up to a 90 amp alt via a single A belt. I can pull 50 amps continous, anything more gets the engine too hot. I can pull about 65 amps for a short burst. I use a larger pully on the engine and a smaller one on the alt to up the RPM's a little, I forget the ratio. I made my own field coil controller, works great and was easy to build, I can equalize as well. I have been using this setup for 2 years or so. I live off grid and run the poor thing for hours in the winter. I'd expect 25-30 amps continous out of your motor.

Jonathan

Could you elaborate on your Field Control Method? would like to see what you've
accomplished.

[Mad_Labs]

I don't have a schematic, I just kind of built it. It is a Propeller uC with a TLC2543 ADC and a big PNP transistor in a TO3 package. I also have a current sensor on the output. Essentially the uC reads the battery voltage (temp compensted, of course) then PWM's the transistor on the field coil. The voltage ramps up to 14.4, then tapers off the current. I have the max amps I want to pull programmed in as well, so when the battery bank is hungry the alt output is limited to 50 amps for longer service life of the equipment. I can set the charge voltage to 15.5 for EQ charging, which I do every couple of months or so.

If anyone wants to make such a thing I'd be glad to help. I could hand draw a schematic and take a pic of it, but it is a very simple circuit.

Jonathan

[rl71459]

I would like to see how you did it.... Sounds like a interesting project. I always like to see different methods to solve a problem.

Rob

[injin man]

I don't have a schematic, I just kind of built it. It is a Propeller uC with a TLC2543 ADC and a big PNP transistor in a TO3 package. I also have a current sensor on the output. Essentially the uC reads the battery voltage (temp compensted, of course) then PWM's the transistor on the field coil. The voltage ramps up to 14.4, then tapers off the current. I have the max amps I want to pull programmed in as well, so when the battery bank is hungry the alt output is limited to 50 amps for longer service life of the equipment. I can set the charge voltage to 15.5 for EQ charging, which I do every couple of months or so.

If anyone wants to make such a thing I'd be glad to help. I could hand draw a schematic and take a pic of it, but it is a very simple circuit.

Jonathan

Definitely post a pic of the schematic, remember many of us here are not EE's but tend to want
to try new things.

[Mad_Labs]

Here is a quick pic. I'm off to work for three days, but if this isn't enough detail I can provide more info when I get home. Note I had a brain fart and labeled the caps as uH instead of uF as it should have been. The caps are tantalum, the transistor is some generic PNP in a TO-3 package. I didn't include the shut-down relay part of the circuit.

Jonathan

[bschwartz]

      "Not everything needs to weigh 1000 pounds and last forever and cost a mint....."

BLASPHEMY!!!!!