Alternator, Battery and Inverter

TobyToby Solar Expert Posts: 56 ✭✭✭✭
I would appreciate any input on this idea.

I have an old 1950's Cub Lo-Boy Tractor. It's equipped with a four cylinder engine with PTO. I had the idea of connecting an car/truck alternator to the PTO via V-belt to supply DC to a 12volt battery and 12v inverter. This would be similar to connecting an inverter to your car but much more fuel efficient. Pully diameter would need calculating for proper alternator rpm.

Inverter would be 120v output @ 1500 watts. Alternator is self-regulating and output would be around 130 amps. Battery, just a standard car battery.

I'm sure a Yamaha or Honda inverter generator would have the same desired outcome. Just an idea. What do you think?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Alternator, Battery and Inverter

    How big is the engine in that tractor? Smaller than the car, but larger than the alternator needs I'd bet. So it would be more efficient than feeding the car gasoline but not as efficient as an inverter-generator. On the other hand it probably isn't going to cost you the price of a generator to find out.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Alternator, Battery and Inverter

    You could do that, don't know how efficient it would be. You can also get a Generator End that would run right off the PTO shaft and mount to your hitch. Check Northern tool.com I don't know the Horse Power you have, I'd think it'd run a 8-10 KW. Do some Google searches.

    Here is a guess on HP needed, yours might be rated in shaft HP.

    10 KW 25-28 hp

    12.5 KW 32 hp

    15 KW 36 hp

    20 KW 42 hp
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Alternator, Battery and Inverter
    How big is the engine in that tractor? Smaller than the car, but larger than the alternator needs I'd bet. So it would be more efficient than feeding the car gasoline but not as efficient as an inverter-generator. On the other hand it probably isn't going to cost you the price of a generator to find out.

    From what I can find based upon the serial number, the engine is only 60 cubic inch and somewhere between 10 - 15 hp at its rated 1600rpm. PTO is rated @ 11 hp.

    Is my math correct on the alternator amp output to power a 1500 watt inverter? 1500watt / 12v = 125 amp.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Alternator, Battery and Inverter

    I have looked at PTO generators. Problem is, this tractor does not have a splined PTO. Just a belt pully to drive a mower deck.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Alternator, Battery and Inverter
    Toby wrote: »
    From what I can find based upon the serial number, the engine is only 60 cubic inch and somewhere between 10 - 15 hp at its rated 1600rpm. PTO is rated @ 11 hp.

    Is my math correct on the alternator amp output to power a 1500 watt inverter? 1500watt / 12v = 125 amp.

    Well yes, and then again no. :D
    1500 Watts / 12 Volts is 125 Amps but:
    1). the inverter doesn't run directly from the alternator, it runs from the battery. The alternator recharges the battery. The inverter's power demands will not be a constant 125 Amps.
    2). the inverter itself will draw power which is not included in that 1500 Watt rated output.
    3). the inverter probably has a surge rating which, depending on how much and how long, will actually cause it to draw a bit more power from time to time if needed.
    4). the '12 Volts' is actually a sliding scale ranging from a high of the full charge Voltage (over 14) where the least amount of current is drawn to a low of the shut off Voltage (often too low at 10.5) where the maximum current is drawn (for any given amount of Watt output).

    But it will be around 125 Amps at full power. With the varying current draw on the battery the alternator should have no trouble keeping up with the charge demands.
    By the way, that 1500 Watts is only about 2 HP. So no problem with an 11 HP PTO. One caution; alternators are not designed to be mounted shaft-vertical.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Alternator, Battery and Inverter

    Before the debate gets to heated.

    I hope never to put full demand on the inverter, but your info is appreciated. Probably would be a good idea the go 10-20% higher on the altenator amp rating.

    If I do this, the alternator will be mounted as it would be in a vehicle. The PTO is off the rear with a nine inch diameter pully. Would just need to fabricate a bracket and source a v-belt.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Alternator, Battery and Inverter

    You would get better efficiency by adding a battery or two and run off of them until they hit 50% DOD, then use the PTO + alternator to recharge them as quickly as possible within a safe amperage range. This is the same general idea as my Prius setup (see my signature link), which gets the same efficiency as a 1-2 kw Honda inverter-genset. The battery is the primary driver and the engine/generator runs just long enough to recharge the battery then turns off again. Letting your tractor engine run all the time won't get you anywhere close to the efficiency of a Honda. It won't be any different than running a car engine at idle.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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