Author Topic: Speed increasing belt drive  (Read 5054 times)

millman56

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Speed increasing belt drive
« on: September 10, 2012, 11:18:35 PM »
Recently I visited a 100 year old water turbine which was repaired and reinstated about a year ago, it is a Gilbert Gilkes and Gordon (still in business) Francis Wheel and is driving an 8 pole 18.5 Kw grid tied induction motor via a speed increasing vee belt drive, 4 groove "B" section 32" to 6".   The setup has over 8,000 hours on the original belts and apart from 1 belt sitting a little lower in its groove than the others they`re showing little wear and a look at the slide rails shows the motor has been adjusted less than an inch in a year of 24/7 running.           It was putting  14.4 Kw into the grid and this would be a good average as on commisioning it was doing over 15.       
Although this drive is operating in ideal conditions, clean, dry,cool and smooth prime mover/ load characteristics,  it still says a lot for a conventional belt drives durability.
Does anyone have any data for the life of belts fitted to a SOM set ? It would be interesting to know how a pulsating and oily prime mover affects belt life.

Mark.

Combustor

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Re: Speed increasing belt drive
« Reply #1 on: September 11, 2012, 02:39:37 PM »
         Yes, the common V-belt is still quite an efficient and long lived device, provided that the belt MAKER'S RECOMMENDATIONS are followed. Loads, speeds, number of grooves and pulley sizes are all specified, and when these are followed they are a quiet, long lasting power transmitter.  Common mistakes I see are using pulleys too small, not enough grooves, misalignment and dirty environment.
             Cast iron is THE pulley material of choice except for low power short run jobs. Unfortunately pulleys are sold in sizes much smaller than recommended minimum sizes for the various belt types.
Because you can buy a pulley does not mean it will be suitable.  An A section belt needs a pulley of 4" or bigger. The B section needs 6" or more, and so on. Sure you will see smaller pulleys under your car hood, but an auto belt wii be a raw edge type, possibly with a cog pattern top or bottom, and is only a distant relative of the industrial belts you will buy in longer sizes for your generators .
So forget small auto pulleys . You will drive your car less than 1000 hours a year and the belts will be changed at the service interval. They probably absorb a couple of horsepower from your car, but your 6 or 8 hp generator can't afford it. So Google up your belt makers info and use it when designing a setup and you will not be disappointed.
           Lister knew all this when they built the CS powered gennys in the 1930"s with 11 or 12" pulleys on the driven end, and they ran forever with maybe an annual adjustment, and only moderate tension. My VA  SOM holds frequency and runs a full load with quite visible slack in the belts. No oil seems to get to the belts on this or my 8/1 when the crankcase breather is doing its job, as they do when correctly assembled.  Modern automotive polyvee belts are popular on the grounds of slightly less power loss, but they sure need some extra tension on flat flywheels to prevent slippage.
           Just the thoughts of a bush mechanic,    Combustor.
Toys include- Lister CS 8/1, Lister VA SOM plant and some Aussie engines.
   "Old iron in the Outback" Kimberley, West Australia.

millman56

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Re: Speed increasing belt drive
« Reply #2 on: September 12, 2012, 02:44:01 AM »
Combustor,    the turbine drive is near the maximum of  Fenners  power rating for this application, according to their very useful drive design handbook.  An 8-1 SOM drive ( 2 X B section belts )  I suspect would probably be rated at much more than its 4.5 Kw , the ones I`ve dealt with  usually have the belts perished through age and I have never seen any noticeable wear on the pulleys fitted to what I guess would be high hour SOMs.   Out of interest I will have a look to see what the max power rating is for an SOM belt drive system.

Mark.

mobile_bob

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Re: Speed increasing belt drive
« Reply #3 on: September 12, 2012, 04:22:55 AM »
i would expect a pair of B section belts coupling a single cylinder diesel and a genhead
would handle easily 20hp, and over that if they are BX (notched) belts.

and i would expect them to rot off before they wore out, unless the unit is left out in the weather to fend for itself.

as for efficiency, my bet is dual B section belt drive on a SOM or any similar constructed generator (meaning cast iron pulleys) to be no worse than 2% in losses.

a serpentine might beat that by a half a percentage point, but i wouldn't go chasing that half point
if i had a SOM with V grooves to start with or good quality cast iron pulleys.

engineered drives that are done right, (ample size pulley's, good materials, and proper wrap contact,  belt tension, etc. will run very efficiently and last longer than one has any reason to need them too)

where belts get a bad name is with the use of pot metal pulleys, or stamped steel, cheap belts that are too small,  improper tensioning, contamination  and other factors that any reasonable diy'er would avoid to start with. 

bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

millman56

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Re: Speed increasing belt drive
« Reply #4 on: September 12, 2012, 07:04:28 PM »
A quick look through my Fenner drive design manual showed timing /synchronous belt drives to be capable of handling enormous power for their size and due to their light weight also capable of very high speeds, no info on efficiency but I would guess very good. As an experiment I rigged up an ST1 running at 1500 rpm driving a 3000 rpm 4Kva Markon alternator  using a diesel cars ( Rover 400 I think ) cam and crank pulleys and a belt off something else, no margin for misalignment with this setup but it made a compact inexpensive ( free )  drive.

Mark.