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Author Topic: Horsepower calculation  (Read 9380 times)

guest23837

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Horsepower calculation
« on: March 03, 2016, 11:11:36 PM »
Hi guys, I have a little lister LT1 engine and a 2.4 kw alternator that I want to drive via a belt. This is only for power outages and will need to power two 20 watt low energy bulbs, a fridge, and a 400 watt UPS for the television. I have a 5" round billet about 40mm thick that i'd like to get a pulley made out of. The engine manual says 2.5 BHP at 1000 RPM and 4.0 BHP at 1500 RPM. for 3000 RPM on the alternator I'd need 1250 RPM on the flywheel. Is there any method of calculating how many HP it's producing at that speed? Apologies for the convoluted wording! Thank you

Thob

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Re: Horsepower calculation
« Reply #1 on: March 04, 2016, 02:00:58 AM »
A first guess would be to do a linear interpolation between the two figures.

((4.0 - 2.5) / (1500 - 1000)) * (1250 - 1000) + 2.5 = 3.25 HP

Which should provide around 1.5 KW electrical output from the generator.  Should be enough if the fridge isn't too greedy.

YMMV
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guest23837

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Re: Horsepower calculation
« Reply #2 on: March 04, 2016, 08:29:28 AM »
Thank you very much, man I wish I'd listened more at school. Would I be better buying a 6" pulley and running at 1500 RPM? Does anyone have any views on taper lock pulleys? Would a single belt be enough? The fridge is 'A' rated so I assume it wouldn't be too greedy?

38ac

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Re: Horsepower calculation
« Reply #3 on: March 04, 2016, 12:01:10 PM »
I must admit to having no hands on experience with the LT series engines but with the older Lister air cooled engines the vast majority had fixed RPM governing. If so equipped you will need a spring at the least and possibly governor weights to change the RPMs.  If you do have variable speed governing that is a definite plus and I like the RPMs under  1800 if for no other reason the engine is a whole lot less annoying when operating. Slowingthe engine does lower HP output and must also be considered as you have found.

 How many and what size belts you use depends on your pulley diameters.   Larger pulleys require fewer and smaller cross section belts than small ones.  Dodge/Reliance has excellent engineering handbooks that last I looked were available on line, if not I have the books on the shelf and can look things up. My seat of the pants guess would be that 2 A section belts would be required to transmit that load over 6" pulleys.

 As for pulley types be aware that what people commonly call a "taper lock" pulley is actually a "QD" type. The QD is what you want easier to mount correctly and much easier to remove down the road. The QD uses hex head cap screws while the Taper lock uses Allen screws that have an annoying habit of stripping out when you need to remove them down the road a piece.  Ebay is your friend for such with surplus pieces selling for 10-25% of retail.  

QD bushing


Taper lock Bushing

« Last Edit: March 04, 2016, 12:08:58 PM by 38ac »
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guest23837

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Re: Horsepower calculation
« Reply #4 on: March 04, 2016, 12:54:35 PM »
QD bushings are interesting but not readily available in UK/Ireland. I suppose I could have a pulley for a ribbed belt made with a key? The LT1 is quite small, it's build 10 and according to the manual can be adjusted from 1000 to 1500 RPM via the governor. I'd prefer not to mess around with weights just yet as it seems I'd need special tools for seals etc. As it would only be used occasionally maybe the taper bush pulley would do? I agree about the lower RPM the little petrol generator I currently use is 3000 RPM and extremely noisy. Thanks for the information, JD

Combustor

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Re: Horsepower calculation
« Reply #5 on: March 04, 2016, 01:29:35 PM »
Your little LT1 will govern better and sound happier at 1500 rpm than it will at lower speeds. It is still only running at half its design speed. If it was delivered with a max 1500 rpm rating then the injection timing will be set for that speed range. If the nameplate says max 3000 rpm then it is worth retarding the fuel timing to make it sound happier and more efficient.
       Engines specified for generator service usually have a governor set for closer speed regulation than a general purpose engine. You may find load response a bit slow at 1500 rpm, but with lighter or non-critical loads this may not matter. Fuel economy is hardly a factor if it's just for outages so easy to set up a simple 2:1 pulley ratio and let it loaf along at 1500. Good luck,
Combustor.
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dieselgman

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Re: Horsepower calculation
« Reply #6 on: March 04, 2016, 02:48:11 PM »
The most prolific use for the LT in North America is for DC charging on highway sign boards. An extension shaft is used off the flywheel and a single automotive v-belt is used on quite small pulleys to run small automotive alternator. Slow speeds and excellent fuel economy is their claim to fame. Governing is not an issue in that configuration but they do normally use a fixed speed setup that does include a speeder spring with an external adjustment.

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guest23837

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Re: Horsepower calculation
« Reply #7 on: March 05, 2016, 08:21:07 AM »
Guys thanks for replying. I have thought about a 12v alternator, a battery and a  power inverter. I don't know enough about what output I'd need from the alternator, size of battery and inverter etc. I suppose one advantage would be I could use a pure sine wave inverter instead of a ups? I have a couple of VW alternators but the pulleys are very small I think they produce 65amps. I dont have the flywheel extension shaft, my engine was on a concrete mixer, it's got little wear on the engine and I believe it was stopped with the de-compressor and thatís what damaged it. I also have a very low income! I could run a ribbed belt off the flywheel I have a 4" ribbed pulley how  to attach to an alternator is a problem? Any ideas suggestions welcome!

dieselspanner

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Re: Horsepower calculation
« Reply #8 on: March 05, 2016, 09:49:55 AM »
Hi John

Check out this post from Starfire for useful stuff about using alternators, amongst lost of other information

http://listerengine.com/smf/index.php?topic=7407.0

Cheers Stef
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dieselgman

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Re: Horsepower calculation
« Reply #9 on: March 05, 2016, 11:15:17 AM »
The engine and alternator may be bracketed together (most common setup), or you could mount both on a skid base of simple manufacture. Scrap steel is common in most parts that can be re-purposed.

dieselgman
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guest23837

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Re: Horsepower calculation
« Reply #10 on: March 05, 2016, 04:16:40 PM »
I must admit to having no hands on experience with the LT series engines but with the older Lister air cooled engines the vast majority had fixed RPM governing. If so equipped you will need a spring at the least and possibly governor weights to change the RPMs.  If you do have variable speed governing that is a definite plus and I like the RPMs under  1800 if for no other reason the engine is a whole lot less annoying when operating. Slowingthe engine does lower HP output and must also be considered as you have found.

 How many and what size belts you use depends on your pulley diameters.   Larger pulleys require fewer and smaller cross section belts than small ones.  Dodge/Reliance has excellent engineering handbooks that last I looked were available on line, if not I have the books on the shelf and can look things up. My seat of the pants guess would be that 2 A section belts would be required to transmit that load over 6" pulleys.

 As for pulley types be aware that what people commonly call a "taper lock" pulley is actually a "QD" type. The QD is what you want easier to mount correctly and much easier to remove down the road. The QD uses hex head cap screws while the Taper lock uses Allen screws that have an annoying habit of stripping out when you need to remove them down the road a piece.  Ebay is your friend for such with surplus pieces selling for 10-25% of retail.  

QD bushing


Taper lock Bushing



I'm thinking the Allen head screws could be replaced with hex bolts with the same thread?

broncodriver99

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Re: Horsepower calculation
« Reply #11 on: March 05, 2016, 04:23:50 PM »
I'm thinking the Allen head screws could be replaced with hex bolts with the same thread?

The Allen head screws go in the recessed pockets of the taper lock bushing. There is not enough room to get a samed sized hex head screw in there. As mentioned the QD bushing is a much better system.

guest23837

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Re: Horsepower calculation
« Reply #12 on: March 05, 2016, 04:46:52 PM »
The engine and alternator may be bracketed together (most common setup), or you could mount both on a skid base of simple manufacture. Scrap steel is common in most parts that can be re-purposed.

dieselgman

Hi Gman, there's plenty of scrap iron for making brackets etc. If I use a car alternator the pulley is usually a clutched pulley about 1.5 inches across. This would make it very difficult to attach any kind of larger pulley without specialist machinery that I have no access to. I have a round 5 inch aluminium billet slice but I'm wary of having it turned as they re like hens teeth here. There are Lucas alternators with a V pulley again the pulley is quite small but would maybe be easier to fit a larger pulley. The larger 230v alternator might be the simplest?

Do you know if the engine could be modified with governor weights? If I adjust the spring to it's maximum would it stay at 1500 RPM? I'm thinking the speed isn't critical for lights and the UPS will have a battery anyway? Thank you

dieselgman

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Re: Horsepower calculation
« Reply #13 on: March 05, 2016, 05:49:05 PM »
There are six different governor weight pairs for the LT1 for all the different build specs. Your unit will have weights and you should be able to govern to 1500rpm, just try it out and see how it behaves.

dieselgman
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guest23837

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Re: Horsepower calculation
« Reply #14 on: March 05, 2016, 06:38:10 PM »
There are six different governor weight pairs for the LT1 for all the different build specs. Your unit will have weights and you should be able to govern to 1500rpm, just try it out and see how it behaves.

dieselgman

My engine is build 10, according to the manual this engine doesnít' have weights from engine number 36 02475, can this be correct? Thank you