I just scored a 79cc, 2.5hp engine from Harbor Freight for $59. I would like to attach a 10SI Delco alternator to this engine.
How many amps @ 12v should I be able to produce with this engine? Will I be able to spin an 85A alternator...or is that asking too much?
Also, could I direct drive it at 3600 RPM rather than using a belt and pulley?
you might do around 30-40 amps continuous, however
the regulator is going to be your enemy
when the battery to be charged is low, it will start to full field the alternator, which in turn
places a very heavy load on the little engine.
you really need a current limit regulator/controller either of which is expensive and hard to implement with a 10si delco.
direct drive is going to be your best bet in my opinion.
bob g
Really...that low? I have a 10SI already that I wanted to rebuild, and replace the stator with one sized right for the engine. (Maybe a 37 amp?) With a 3 wire regulator I should be able to use a rheostat to control the field...shouldn't I?
This is basically what I want to make:
http://www.alten-dc.com/products/item/107-12-volt-80-amp-gas-powered-battery-charger.html
They're claiming 80 amps but that engine has a bit more power.
(can anyone identify what type of alterantor they are using there?)
if you can control the field and set it up for direct drive, you might be able to pull more amps
only one way to find out!
;)
bob g
By the case style and the black rear unitized removable brush holders and regulator assemblies these unit are either Robert Bosch alternators or Chinese clones of the same. Unlike an SI Delco alt these Bosch are easily convertible to externally regulated. 1970-71? first year era 10SI's cased units have no internal regulator and were for existing equipment wired for external regulation. Internally regulated have the two blade regulator terminals side by side inline with each other. Externally regulated have the "field" and "relay" blade terminals parallel with each other. Most rebuild shops have these hollow factory internal terminal spacer blocks laying around. If you are sourcing small cased Delco's, the plastic vacuum fanned 12SI's have a much lower cut in and lower RPM output capability. There is much more metal in the rotors and the stator lamination stack is thicker. Of course use what you got always.
Regards
Steve Unruh
Is there an alternator I can get for less than about $100 that might work better? How would I regulate an externally regulated alternator? Is there a cheap regulator I can buy to use for now, and then get a fancy 3 stage charge controller in the future?
you might consider this regulator
http://cgi.ebay.com/ebaymotors/Sterling-Power-Marine-Advanced-Alternator-Regulator-B-_W0QQcmdZViewItemQQhashZitem4aa23cbcd8QQitemZ320549469400QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear
they have a number to call, and you might check with them about the regulators use in your application, as to whether or
not it can tailor the output amps to the available power of your small engine.
at 109 bucks it is close to your price point, and if it will do what you need done...?
i have many different controller regulators, from balmar, xantrex, amplepower and hehr, all of them have a way to tailor the output
amps to match the available power of the prime mover, however i have no experience with sterling so i can't tell you what is possible with
their products.
bob g
Watts are watts reguardless of the source. 2.5HP should be good for 1250KW.. P over I X E tells me that 1250W divided 14 VDC equals 89A of current draw. The 2HP/KW rule usually covers you for generator efficiencies, but with auto alternators being supposedly less efficient, this number may be way out to lunch:)
Cant you just use an 30 thru 40 amp version of the alternator to closer match the engine?
In my drag racing days... I built a compressor/alternator rig using an old Ford Reciprocating AC compressor and a GM Internal reg alternator. Used a 2 Groove alt pulley on a Clinton 2hp (I think) with one belt going to the Compressor and another to the Alt. I made a Throttle Solenoid out of a Chevy starter Sol (Pulled a Cable for High speed) and used the contacts to switch between Alt to compressor when the pressure switch called for it. It had a CO2 tank for air. It worked great! I had people at the track's copy it more than once.
Use went something like this... After a run (1/4 mile) then return to the pit's I would connect the rig cables Via Welder Jacks to the car. and start the engine, Running at the "Low Speed" (Sol not pulled in)
it would charge the battery in the car, As the battery recovered you could hear the engine load drop.
If the pressure switch called for air it (Via Contacts) shut off the alternator (Dropped Field) at the same time pulled the sol (High Speed) and the contacts in the sol would energize the clutch on the Compressor.
once the tank was full the pressure switch dropped out the solenoid (Low Speed) and re-enrgized the alternator.
I used that thing for many years... Never let me down at the track. Sometimes when needed I would use it for Charging a car up in remote location. It was handy!
Rob
I now remember it had a switch so you could run it unloaded when warming up the engine with the cables still connected.
also the pulley arrangement was a 1:1 ratio due to the fact that the engine pulley was indeed a alternator pulley.
as I'm describing/writing this it sounds like it should not work very well... But it worked great! can it be that the small alt and slow rpm were working in my favor? does the alternator slip at low speed? Whatever the reason it worked good for many years of use.
here is the math
2.5 hp = ~1862 watts
1862 watts x 45% (alternator efficiency and drive losses at max output) = 838 watts
838 watts / 14 volts (approx charging voltage)= 59.86 amps
that is about 60amps maxed out, if the engine is in perfect running order, at sea level, on a cool day, running good gas
with your mouth held just right, however... do you think you can run the engine at max output for very long? or would you want to?
the engine will also have to be running at full rated rpm to achieve this output, not many of these engine's are designed for such duty.
probably better to derate to around 70% which would give you about 41.9amps continuous capability, which is probably more inline with
reality in my opinion for a useful unit that can be depended on to run at that level at the drop of a hat and do some useful work.
the real issue with trying for more power is related to how the alternator oem regulator (if you use that), it will try to immediately go to
max output before the engine has had a chance to startup, get to speed and become stable. the alternator will make it nearly impossible to start
and get up to stable operation. if you use a programmable controller you can set the warm up time to allow for a no load startup and time for the
engine to come up to speed, run long enough to get to operating temps and stabilize before the alternator is gradually brought on line either in steps of a soft ramp up.
i am not saying it is impossible to get more than 40amps or so from a 2.5hp engine, just that it might not be as reliable and difficult to get started
and into operation.
bob g
I've got a 62 amp 10 si belted up to a Tecumseh 5hp engine with a 5" pulley on the engine and 4" on the alternator. If the battery is low it will frequently kill the engine when the field is connected. It will usually stay running if rev'ed to 3600 rpm. After it's connected and charging the rpm's can be reduced to around 1800. I made it to extend the run time on our household backup battery/inverter system. Its also good for a fast charge on a car/tractor with a dead battery and it's been used to charge RV batteries with good results too.
Quote from: mobile_bob on April 25, 2011, 06:51:45 AM
you might consider this regulator
http://cgi.ebay.com/ebaymotors/Sterling-Power-Marine-Advanced-Alternator-Regulator-B-_W0QQcmdZViewItemQQhashZitem4aa23cbcd8QQitemZ320549469400QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear
they have a number to call, and you might check with them about the regulators use in your application, as to whether or
not it can tailor the output amps to the available power of your small engine.
I like that! If that would work with the Delco alternator I already have it would be perfect...
Quote from: rl71459 on April 25, 2011, 08:44:41 AM
Cant you just use an 30 thru 40 amp version of the alternator to closer match the engine?
Well, that is the main question. I don't want to use an alternator so big that it will kill the engine, but at the same time, I don't want to cut myself short either...
After a bit more research I can see that this engine is a clone of the Briggs and Stratton 2.4hp Vanguard engine...about $400! :o Here's the HP/torque curve that Briggs supplies...
Quote from: mobile_bob on April 25, 2011, 09:55:36 AM
do you think you can run the engine at max output for very long? or would you want to?
the engine will also have to be running at full rated rpm to achieve this output, not many of these engine's are designed for such duty.
Say what? Nearly all cheap generators run at a fixed 3600 RPM, whether you need the speed or not! I finally fired up my engine tonight and it ran so smooth even at 3600 that I didn't even have to bolt it down to anything. Very impressed with it...not obnoxious sounding at all.
Looking at the Briggs HP curve they recommend a max load of about 2hp or 1.5kw.
Is there a good rule of thumb that can be used with alternators and amps per HP, similar to how we always estimate 500 watts/HP with a normal generator?
the rule of thumb for gas engine driven alternators is 25amps @ 12 volt nominal per hp of engine, that being for a good engine
well tuned, and with the proper drive ratio
in my opinion that is perhaps a bit optimistic in real life, my thinking is 20amps per hp is more likely over the long run.
that might have more to do with the engine oem hp claims being at times more than optimistic,
if your engine will do 2hp continuous, then 50amps is possible if you drive it correctly.
bob g
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.
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
Quote from: Derb on August 06, 2011, 04:15:03 AM
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....
Quote from: Derb on August 06, 2011, 04:15:03 AM
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
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.
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.
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.
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.
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.
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
Quote from: Mad_Labs on August 11, 2011, 03:18:57 PM
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.
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
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
Quote from: Mad_Labs on August 14, 2011, 09:58:08 AM
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.
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
"Not everything needs to weigh 1000 pounds and last forever and cost a mint....."
BLASPHEMY!!!!!
Bio - Did you ever get this project going? I am interested in doing a project along these same lines. A standard 63 amp 10si puts out approx 46 amps at 3600 RPM. So 46 x 14.5 v = 667 watts. A direct coupled 3 HP engine should have no problem pulling this load unless I am missing something. I would put a switch in the circuit to allow the engine to warm up prior to energizing the alt.
Bob
Unfortunately I haven't had a chance to put this thing together yet, I've got the alternator and the engine I just need to fab up a drive system. Most of the parts kinda got lost for a while as I've moved my shop twice since I made this post... ;D
I was hoping to import some ready made small 12v generators using this same engine using a PMA, but unfortunately the talks with the company in china didn't go well...
I built one with a 5hp Tecumseh and 10si, but it is belted 7" on the engine to 4" on the alternator. At this ratio the engine needs to be rev'ed to full rpm's before the field wire can be plugged in. If the engine is accelerated from idle as soon as the Alt cuts in it kills the engine. What I do with mine is connect to the load, start the engine, allow it to warm up a bit and then rev the engine and plug the 2 wire side connector into the alt to start charging. It runs around 1800 rpm to reduce noise and fuel consumption.
A 3hp direct drive will probably work ok. I build mine to extend the runtime of a 12v inverter/battery system that ran my house during extended outages. I used to live in the Redwoods and when big storms came through the power would go out for a week at a time. It did teach me how to live off-grid though.