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Small Cabin Forum / Off-Grid Living / Battery Charging with an auto Alternator
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kittysmitty
Member
# Posted: 10 Nov 2021 15:55
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In November the cabin get's the most use and unfortunately the time with the least amount of sunshine. This would be my 3rd generation charging system. Started with a lawn mower engine and a small belt drive auto alternator. The latest is a 5.5 hp power washer engine and a 140amp Delco alternator direct drive using one of these, https://theepicenter.com/coupling-l-095-modified.html I can't seem to have a spider that lasts very long. I switched to Hytrel Rubber spider and that didn't help. Am I asking too much? Is the coupler undersized? Thoughts? Suggestions? Thanks

gcrank1
Member
# Posted: 10 Nov 2021 20:31 - Edited by: gcrank1
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I started like that back in about '85, the little B&S engine couldnt spin the Toyota car alt fast enough to much amps out of it. The faster the alt spins. the more it outputs and the more hp it takes to turn it. I struggled with it off/on for a couple seasons but had better luck just taking 1 or both DC Marine batteries home to charge. We did that for decades, and when the bats wouldnt give our energy hog 12vdc Edison base RV bulbs enough to actually be bright we'd fire up the oil lamps. Plus the thing was NOISY and Far Too Long.
I also had trouble with the coupling. Alignments are Critical, dont depend on a coupler to compensate unless low load, low rpm.
Game Changer for Us:
All LED lights! We wired for 120vac and run everything from the bat-bank to the 300W Pure Sine Wave inverter. That 300W PSW is for our everyday lights, usb and tool chargers, small tv/vcr; ie, 'light draw' stuff. When I want/need to run off the gen for 'big stuff' like the microwave, etc. I start the gen, unplug the line from the inverter and plug into the gen 120v outlet. Easy-peasy.
We bought a little Champion Inverter Generator, iirc it is 1700w continuous, 2000w peak, still at about $450 at our TSC store. It runs my power tools, 700w microwave, 1000w hot water heater, etc. and the automotive 120vac 20amp smart-charger for the bat-bank IF needed (but only one at a time). Don't bother with 12vdc charging even if the gen has 12v taps, the amps arent high enough.
Im pretty sure the Lil' Champ would run a bigger charger, my 20a is what I have and my cabin solar is 600W for currently 2x 12v/100ish ah bats (it will work for 4x 100+ah bats though).
Btw, the Lil' Champ (my name for it) is easy on gas, quiet, and only about 45# so easy to move. They do make a dual-fuel model for a bit more if you would like to run on LP gas.

paulz
Member
# Posted: 10 Nov 2021 20:55
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I have a coupler like that on my log splitter. 10hp Briggs, 1 inch shaft I believe. Never been a problem but it only has to work intermittently for short bursts.

Bruces
Member
# Posted: 11 Nov 2021 07:22
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I have dealt with (mechanic in the Arctic ,mine sites ,heavy equipment shops ,truck shops etc ) like that on tons of equipment and for the most part they have worked perfectly well with no failures .I bet you have an alignment issue between the alt and the engine that is just enough to cause you grief .If the coupler is a real problem ,I would use a belt and pulley arrangement instead .Getting way off topic ,I have made generators like this for service trucks ,my airplane etc ,and we always had great luck with the old (pre 1986) Chrysler 100 amp alternators ,I can’t remember ever having to replace one and they can be had very inexpensively ,nothing wrong with delco units but the Chrysler ones just lasted forever .Of course a simple inexpensive external voltage regulator was required for the Chrysler unit .
Have fun !

toyota_mdt_tech
Member
# Posted: 11 Nov 2021 15:38
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Why 140 amp alternator, way too heavy of a load, try something like a 60A or even a 42A unit.

kittysmitty
Member
# Posted: 13 Nov 2021 16:18
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140 amp to reduce the run time.

gcrank1
Member
# Posted: 13 Nov 2021 16:59 - Edited by: gcrank1
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A battery bank needs to be charged at no more than the rate the battery manufacturer specifies. This is especially important with lead acid batteries.
LFP can be discharged/recharged safely at a high rate.
I dont think that alt will make peak power at the rpms the engine runs at anyway. Have you measured the actual charging amps running?
Unless you go to great lengths to get the engine and alt shafts perfectly straight, not just 'matched up' at the coupler, you will have issues. I recommend using a belt drive also if you must stick with this. With, say, a 2:1 pulley ratio, and enough hp to drive the alt under load, the alt could spin at twice the engine rpm so the engine could possibly be run slower, be quieter and use less gas.

kittysmitty
Member
# Posted: 14 Nov 2021 16:48
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Haven't measured the charging amps with a meter, but with a 100amp hour battery, inverter and 1000 watt ac load the battery voltage will remain constant at around 13 volts. so, at least 75 amps with out calculating any loss.
The engine turns at 3600 rpm so I am not getting peak amps out. Today, the fan started to scrap the bracket, so I know the aliment is an issue.
Time to work on Generation 4 with a belt drive, more forgiving and as you suggested and with a 2 to 1 ratio will spin the alternator faster for more output. An added benefit might be increased cooling with a faster fan speed.

gcrank1
Member
# Posted: 14 Nov 2021 16:52
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Do you have a tach on the engine to know its actually turning 3600rpm, that is really spinnin'.

kittysmitty
Member
# Posted: 16 Nov 2021 19:06 - Edited by: kittysmitty
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No tach, but manufacturers specs. And comparing alternator power curve to output, 3600 rpm is about right

kittysmitty
Member
# Posted: 23 Nov 2021 17:02
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gcrank1. you mentioned a 2 to 1 ratio. I assumed it was pulley diameter, but was told today it was circumference.
Which is it? Thanks

gcrank1
Member
# Posted: 23 Nov 2021 19:37 - Edited by: gcrank1
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I used that statement as an example not necessarily a recommendation. The caveat I mentioned is that you have to have enough hp to drive the increasing load produced by the alt/gen as it spools up and is creating more electricity.
Think of the pulley as 'gears with no teeth'; ie a 36t driving a 18t will make the 18 spin twice for every one of the 36. So, yeah, the teeth are on the outside, the circumference.
This with pulley assumes no slip.
Fwiw, on my too small an engine I couldnt use a big enough pulley to drive the alt with the pulley it came with to produce the charge I needed.
Ymmv
As an afterthought regarding charging In general, the gen charging with a vehicle alt/gen is good for bulk charging; just what it was intended for. Not so good for the absorb phase which properly takes far longer with diminishing amps going in. Noisy and inefficient that.
But we do what we gotta do.

Bruces
Member
# Posted: 24 Nov 2021 09:28
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It takes about 1hp to turn every 25 amps of alternator as a general rule ,you “currently” have nothing left to play with so messing with gearing you will need to keep it pretty tame .

gcrank1
Member
# Posted: 24 Nov 2021 10:10 - Edited by: gcrank1
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Maybe I did something wrong?
My 3.5hp B&S belt drive to an little old Toyota car alt never made 25amps output at any rpm including wide open, an rpm I most certainly did not want to have to run at. At the time I had a direct drive tachometer for my trials.
I tried to find an rpm I could stand and get as many amps as possible, various pulleys on engine, as expected, as I went up in size the drive torque went down. The 'happy place' engine rpm for having to listen for about two hrs every morning (in an otherwise quiet woods) just could not put enough amps back in to make up for the prev night mostly 25w incand. rv light bulb (25w/12v=2+amps per hr) so figure about 15a discharge. I was always in deficit 'spending'.....That told me I was gen'ing less than 7ish amps out of that Toy alt. The more the deficit added up the worse it got.
Total fail unless I would run it most of the day?

Fanman
Member
# Posted: 24 Nov 2021 21:07
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3.5HP is 2610W, so it should be more than adequate for any normal car alternator, but you need to select pulley sizes to spin the alternator at its design rpm. 2610W at 13.5V that is nearly 200A.

140W is only 10.4A at 13.5V.

Of course if you're charging a battery through a regulator (or modern internally regulated alternator), the current is only what the battery is taking which decreases as the battery charges, not necessarily the maximum capacity of the alternator.

Pulley ratios, diameter ratio or circumference ratio gives the same number.

gcrank1
Member
# Posted: 25 Nov 2021 10:37 - Edited by: gcrank1
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It would spin fine....until I hooked the leads from the ext reg to a discharged battery (no problem with a charged bat), the heavy amps load would heavily bog the engine. Pulley'ing enough to overcome the bog to get an rpm that was 'not terrible' to have to listen to gave dismal amps charging.
Determined I needed a bigger engine.
In fact, I would have probably been better off starting the truck and jumper cabling to the cabin bat. Ready made charger.
Just my experience in messing around with junk I had.

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