Ok got me a old lawnmower engine and the original 60 amper outa my 77 with voltage reg.

im trying to figure out the pulley ratio i need to use on my lawnmower engine but i dont know at what rpm the alternator is putting out full load. anyone have a chart for these old alts?


-gbm-

 

Well nornally the VR doesn't kick in until about 850 rpm to tell the alt to Pump up the Jam.

 

65amp ford alternators run at maximum output at from 2000 to 2500 engine rpm. You'll need to know the size of the harmonic balancer pulley on that 77 you took it off of

 

thats what i needed to know, ill play it safe and go with 2500 rpm.

heres the math im using.

the engine pulley on the 77 is 8 inches and the alt pulley is 2 3/4 inches

so 8/2.75=2.9:1 ratio
so with the truck engine spinning at 2500 rpm that means the alt is spinning at 2500 x 2.9 =7250 rpm (this is what rpm where looking to spin the alt at)

i know my 3.5 horse briggs lawnmower engine is spinning at 2900 rpm full
throttle so i take 7250 rpm/2900=2.5;1 ratio (thats the ratio i want for the lawnmower engine pulley size)

so i have a 2.75 inch pulley on the alt allready if i stick with that i will need a 2.75x2.5=6.87 inch pulley (6.75 or 7 inch)

what i need to figure out now is are the automotive pulleys the same as industrial pulleys pitch wise and what mounts up to the lawnmower and alt. shopping i will go. ill get back to you later. ill post up pics as i go here.

-gbm-

 

Glad I was helpful. Happy manufacturing!!

 

I would use a large case version of that alternator, it puts out 100A. You can find them on mid 80's Taurus and Merc. Sables.

 

why?


-gbm-

 

One of our local small engine shops used to sell a jump-starter/battery charger that was a standard GM 55A internally-regulated alternator directly coupled to a 3HP horizontal shaft Briggs and Stratton engine. The Briggs engines normally run 3600 PRM full-load, so that is probably how fast they were turning that alternator. Seems about right if the automobile engine is turning 2000 RPM for max charge and the pulley ratio is probably nearly 2:1. They had a direct coupling with the alternator and engine together nose to nose. It was a cute little outfit, and was pretty safe since it wouldn't start putting out any voltage until connected to a battery with enough voltage to flash the field of the alternator and start it charging.

 

Higher output at slower speeds, heavier duty, more surface area to dissipate heat. You will melt your current alternator if you try to pull more than 80% capacity out of it (45a ish). The large case you can get 75a out of safely.

 

I dont follow what your trying to say to me here please explain further.



-gbm-

 

I've got one of these to go on soon..

My amp pulls 40 amps alone

http://rjminjectiontech.com/?p=6

 

There is sooo much info to weed thru to try and explain my reasoning. Ive stolen bits and pieces off of the internet, but could not find all I was lookng for. My brain hurts, so I cannot do any better.




An alternator typically takes about 1 HP (horse power) for every 25 amps of power generated. So, a 100 amp alternator will require about 4 HP at full output. Most alternators do not operate at full output for very long.

<table border="0" cellpadding="11" width="97%"><tbody><tr><td colspan="2" align="center" width="100%">Ford Motorcraft 1G type Externally Regulated Small Case vs. 1G Large Case Alternator </td> </tr> <tr> <td colspan="2" width="100%">
</td> </tr> <tr> <td colspan="2" width="100%">
</td> </tr> <tr> <td align="center" width="50%"></td> <td align="center" width="50%"></td> </tr> <tr> <td align="center" width="50%">Small Case, Left. Large Case 1G, Right</td> <td align="center" width="50%">Small Case, Left. Large Case 1G, Right</td> </tr> <tr> <td colspan="2" width="90%">
</td> </tr> <tr> <td colspan="2" width="100%">For maximum low speed output the best solution is to use a larger size alternator like the example shown above which shows the difference between the small case 1G and the large case 1G. Both are 1G series alternators but, the only components that are interchangeable between the two are the pulley, bearings and a few nuts & screws. In almost all cases, the large case alternator will bolt exactly in place of the small case without bracket modification. You can also use the same voltage regulator from your small case alternator to control the large case unit. The only change, is that the large case alternator requires the use of a plug connection, shown below, for the field and stator leads to the alternator. </td></tr></tbody></table>

 

if anyone wants to upgrade there alternature on our old fords do what I did, i took a 3g 130 amp alt out of a 93 taurus straight from the scrapyard ($30) the mounts were identicle to the stock one in my 77. this is a internally regulated alternature, from what i remember it was 2 wires. 1 was a main power feed to battery (dont use the stock wire it isnt big enough, pull the wire out of the donar car) and the other was the stator wire (i think that wire needed to be switched to the key) that wire also has to have a resistor put into it i got one from the local electronics shop ($.75) i left the old voltage reg and plugs for the alt in the harness and carry a spare original alt in my drybox. you need to switch the pulleys as the taurus used a serpintine setup, the v belt pulley fit right on. i had to try a couple different makes of belts as the 130 amp causes alot more resisitance over the 60 amp so i was chewing up belts.

I run a stereo and all that but my main power draw is the 7 100watt lights i run when im wheeling 700watts/12v= 58 amps

i found all sorts of conflicitng information on the internet so i dug up the wiring diagrams for the 93 taurus and whent to town, going on 3 years no problems, i did tests on that alt and it will put out 130 amps at idel, when i flick my lights on i can actually hear the engine be slightly dragged down for a second.


-gbm-

 

I would go along with the fact most alts dont run at full amperage constantly (duty cycle) but for it to take 1 horse for every 25 amps i dunno thats some pretty large inefficiency, the mathematicle equation puts 1 hp at 745 watts thats 62 amps at 12volts.

My friend was telling me his uncle has a 200 amp alt hooked to a 5hp engine and he sais it nearly stalls when its kicked in. I beleive that to be a resonable ineffiecency level

we will know soon here if my little project works or not. i got the pulley mounted on the hub and mounted to the engine, time to start working on the framework.

i dont plan on using this as a generator for lights or anything like that i want it for charging my camper batteries (2x1100 cca batteries) i used to run my 110 volt gen set with my 15 amp charger but that takes way to much time and it aint cheap to run a 2800 watt generator even at low load. I dont know how long this engine will run on a tank of fuel (its 1 liter) but i compare it to how long it takes to mow the lawn im gonna guess it will run for 45 minutes to 1 hour thats about right to charge my batteries and best of all its self regulating so i just wake up in the morning fire it up with a full tank go hunting for the day and when i get back all is charged and good to go.


might not get finished this set off but ill make sure i post up results even if its a month or so from now.


-gbm-

 

[QUOTE=gingerbreadmaniac]I would go along with the fact most alts dont run at full amperage constantly (duty cycle) but for it to take 1 horse for every 25 amps i dunno thats some pretty large inefficiency, the mathematicle equation puts 1 hp at 745 watts thats 62 amps at 12volts.
QUOTE]



Most gen sets are sized at 500 watts per HP through the smaller sizes. You have 4 HP and need about 1.5, I'm sure you'll be fine.