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Weedeater powerd Alternator?

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#41 ·
I dont doubt Kbeitz's gas powered charger works with 1.5 HP,but it probably has a DC generator in it,not an altenator..you can get 30 amps from a generator with less HP and rpm's than an altenator needs..

I once had a "Goodall" starting unit that had FOUR generators ,bigger than car ones,hooked to a 12 HP Kohler single cylinder engine,in a steel case--..it produced 12,24,36,or 48 volts,depending on the switches you had to flick,it could start anything from a 12V car,to a 24V tractor trailer or construction equipment,even 36 and 48 volt busses and forklifts too...full output was 250 amps!..I did some welding with it on the 36V setting many times..I found it in a junk cars trunk at a junkyard,paid 40 bucks for it..wish I kept it,a friend bought it from me,used it maybe twice,sold the Kohler from it,and he eventually scrapped the generators,I regret not taking them now,when he said too,or they'll go to the scrapyard...
 
#43 ·
thudpucker said:
You guys are 'Fixers'! Your cursed with the need to solve a problem! :)

Did you notice how many different options came up?
I tried phrasing it different ways to catch everybody's interest.

Originally I just wanted to come up with a cheap and dirty, cost reduced batter charger for my fishing boat.

And besides....I might someday go back to Canada to those huge lakes and need the 'Two Battery' fix, and still fish around here for the single battery small lake fix.

I didn't mention the first time I went up the 11 mile lake. I had an old rubber boat that would need patching every time you dragged it up on the beach.
I got out on the beach and the very first thing I saw in the soft sand was some huge Bear tracks.

It was pretty dark. I didn't know for sure where to set up a tent in Bear country, so I got back into the boat, went way out in the middle of the lake and spent the night in my trolling motor powered Water-bed.

That thing lost so much air overnight I was just about sunk by first light.
It was so mushy the trolling motor force folded it up a bit. Bear or no Bear, I had to get to the Beach.

Eventually I had to row most of the Eleven miles back to the ***.
All the way back I was grateful for not shooting a Moose!
I might have had to make two trips with oars. I tried not to think of what I might have been up against if the Bear had discovered my boat on the Beach and chewed it up!

That was in 1972. Weedeaters werent known to me then.
However, right then I knew I'd better come up with some way to re-charge that Battery!

You guys are invited in on the job. You see now, just how exciting some jobs can be eh?
Click to expand...
Yes, it can be done and it all boils down to what you have to work with, what performance envelope you require, and how deeply you want to get into it moneywise.

Someone posted a link to a tiny HF genset. I have one from them that is even older. It has a 2 cycle motor smaller than what you would find on a weedwhacker, and a really good muffler. It runs so quietly that it probably not offend anyone. Now it does not put out a lot of power, but it does have both 120 vac and 12 vdc outlets. I use it in case I need to charge a battery -- as in, the power is out, I need to start my home genset, but the battery is dead. Backup to the backup to the backup. But I digress.....

...the point I am trying to make is that the amount of electricity you generate is a function of how quickly you want to recharge the batteries for that trolling motor. At the high end, you would want to be able to continue running even if the battery was dead - or gone. In this case, you need as much power as that trolling motor absorbs when you are trolling. This should set your high end.

You can have less. For example, say your trolling motor pulls 10 amps at 12 volts and your generator can only supply 5 amps at 12 volts. Well, in this case you are extending your range because the battery only sees a net discharge of 5 amps. So you can go farther on that same battery.

A benefit of the genset is that it can charge the battery even while you are not using the trolling motor. In the 'one-half' example above, when the battery gets real low pull into shore, have lunch, and let the genset continue charging.

Solar panels are not going to help much on a boat as you will not have enough surface area for enough panels to get the high currents you need.

Please note that direct driving the alternator/generator to the crank will require very high engine rpm to produce sufficient power. In your car the alternator is geared up 2 or 3 to one. It can be spinning 6000 rpm while you are cruising at 2000. The only way around this - in other words, to get enough energy out of the generator at a lower engine rpm - is to use a generator with a lot more poles, as are used for water wheels and windmills. But then you are talking about higher cost and soze and weight, so not practical for a small boat. If you are a good fabricator, maybe adapt a Harley alternator since they mount on the crankshaft and yes, you guessed it, they have a lot of poles. You would need to somehow fasten the stator to the engine, and the rotor would be direct coupled to your crankshaft.

Without knowing more about your specific situation or requirements, I would suggest doubling up on the batteries and then looking for a genset combo that would handle somewhere between 50% and 100% of what you need. That would pretty much cover you regardless.
 
#44 ·
Oh yes, for estimating, 1 hp = 746 watts. To allow for inefficiencies, a conservative rule of thumb is that 1 engine HP will produce 500 watts at the load. For 12 volt DC systems, that equates to just over 40 amps.

Also keep in mind that for a gas engine to produce rated power, it needs to be WOT at rated rpm.
 
Discussion starter · #45 ·
Well, I sure want to acknowledge those informative and well said statements.
You guys get an "A" for Report writing!

When I learned about the Torque and Rpm required to re-charge a normal car battery that's been used down below 11 volts, I realized my idea of a Weedeater wasn't going to work. A 5 Hp B&S would work though.
That torquey little guy would run a Standard GM, single wire, self regulating Alternator at 7,000 Rpm while the B&S is running at the std 3,600 Rpm. It has the Torque to run the Alternator at 2:1

I wanted to find a smaller alternator (or Generator and I'd make a Regulator) Something off a Motor Cycle or some other small engine with a 12 V system.
For that, a weedeater would work. It'd just take more time.
 
Discussion starter · #47 ·
Comp, that will come off some old motorcycles etc from the early 60's or 70's.
It will be a rare find. I think Evinrude/Johnsons had a gen/alt that sat on the side and was belt driven from the flywheel. You can imagine that little booger was turning out some R's though. It was about a 10 or 12 to 1 increase in speed with the size of the driving belt shiv much larger than the driven.

I think somebody in these posts, I put this on several different forums, did come up with formula's to show the "Effort" in Watts, to charge a 12V Battery, was more than the little Weedeater was capable of in "Watts".
 
#48 ·
thudpucker said:
Comp, that will come off some old motorcycles etc from the early 60's or 70's.
It will be a rare find. I think Evinrude/Johnsons had a gen/alt that sat on the side and was belt driven from the flywheel. You can imagine that little booger was turning out some R's though. It was about a 10 or 12 to 1 increase in speed with the size of the driving belt shiv much larger than the driven.

I think somebody in these posts, I put this on several different forums, did come up with formula's to show the "Effort" in Watts, to charge a 12V Battery, was more than the little Weedeater was capable of in "Watts".
Click to expand...
Hmmmmmm i have a couple of 31cc Ryobl's ,maybe i could hop one up and add a little nitro :thThumbsU
 
#50 ·
Tractor-Holic said:
it probably has a DC generator in it,not an altenator..you can get 30 amps from a generator with less HP and rpm's than an altenator needs..


/QUOTE]

Sometimes the terms get confusing. Generators are DC. Alternators are AC. The HP and other items don't care if it is AC or DC. (Actually, with AC other factors do creep in, like the power factor, but that is only for inductive or capacitive loads. For our purposes there is no difference.

So, while it may be true that, for a given voltage (say, 12 volts) a particular generator might be able to produce 30 amps at a lower rpm, POWER IS POWER.

12 volts times 30 amps equals 360 watts. Period. The rpms have nothing do do with it.

That's why you can buy a 10 kW generator that spins at 3600 rpm, or 1800 rpm. But both motors would be producing the exact same POWER to produce the 10kW you had paid for.
Click to expand...
 
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