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Messages - timgunn1962

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General Discussion / Re: Engine for natural gas generator
« on: September 20, 2006, 01:19:30 PM »
I'm in the UK with 50 Hz mains. We used to run a converted 260 cid Ford inline six on landfill gas. It made 60 kW max at 1500RPM and ran 24/7/52 for almost 4 years (33000 hours). It only got removed because we installed a much bigger unit. I'd guess you would probably need something around the 120 cid, 2 Litre mark. A converted Gasoline set would be a good option. The biggest problem I could foresee is mating it up with the alternator. If you can get hold of a gasoline generator of about the right size, most of the work is already done. The next biggest problem is the governor system. Again, this is side-stepped by using a gasoline generator. Our set was a Diesel engine, converted to spark ignition. I assume this was at least partly because it was easy to mate the engine to an alternator with off-the-shelf parts.

I know Volkswagen were selling small industrial diesel engines quite aggressively in Europe a few years back. I think they were basically Golf/Rabbit engines so the bits needed to fit an alternator may be available. I can't be any help on US domestic engines, I'm afraid.

Next problem is the carburettor or gas mixer. Our Ford set used an Impco for a while and it worked pretty well. It did not cope well with the varying gas quality from the landfill, so was changed at around 20000 hours for a too-complicated system. We had a couple of converted Deutz engines running on landfill gas, too. These had the most elegant and effective gas mixer I have ever seen. Armed with a small lathe, one could be made in a weekend by the average home machinist. I have no drawings or photos but could scan and email a (very) rough sketch, if you are interested.

You will need to check out your local requirements for gas safety systems. Here we have to fit dual, approved solenoid valves in the supply line. Above some line size, a test unit needs to be used which opens the upstream valve, closes it, waits a few seconds, checks there is still pressure between the valves, opens the downstream valve, closes it, waits a few more seconds and then checks there is no pressure between the valves. If all is well, it opens both valves and feeds gas to the engine.

You may find the cost of the gas supply train and its control are the biggest obstacle you face, especially if you have to buy new.

It is worth checking the gas spec with your supply company. Particularly the limits on "Methane Number". This is a measure of the detonation resistance of gaseous fuels, just as Octane Number is for liquid fuels. Gas from different sources can have very different methane numbers. In the UK, we have North Sea gas, formed at high temperature and almost pure methane, Methane Number near 100. When this runs out, we will need to import gas from wherever we can get it. I have seen specs for Eastern European Natural Gas with a Methane Number as low as 45. Formed at lower temperatures, this has significant amounts of Nitrogen, ethane and ethylene. It probably also has some propane and perhaps some butane in. Generators optimized for North Sea gas are likely to start falling off their perches if fed with something with a MN of 45. Realistically, it's not likely to be a problem, but I'd try to cover all the bases before taking on a big project.

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Lister Based Generators / Re: Any UPS/Inverter Experts Out There??
« on: September 19, 2006, 11:01:34 PM »
I'm no expert. I once tried running a UPS on a generator in the mid-nineties. We had problems with the mains fail detection system sensing every significant deviation from a fixed-frequency sinusoidal waveform as a mains failure, and switching to battery power on an almost continuous basis. This was  a problem with both off-line and line-interactive units, the latter using ferro-resonant transformers to provide a sort of flywheel effect between the mains failing and the inverter switching in. We actually ended up using a rather expensive on-line UPS and had to program it for the widest possible input tolerances.

An off-line UPS runs the inverter all the time, so "should" not need to monitor the incoming supply. If the unit in question just uses the ferro-resonant transformer to clean up the inverter output, all should be well. It appears that it will take a 48V DC supply. If necessary, this could be used and would bypass any monitoring of the supply frequency. Obviously, it would need a suitable power supply; added complication.

I believe the APC smartUPS range are line-interactive, so should provide a source of small ferro-resonant transformers for anyone who may be interested.

3
Everything else / Re: Engine Room Ventilation Fan
« on: September 19, 2006, 10:27:30 PM »
You can run a damper on either the blower inlet or outlet and it's not likely to make much difference to either the temperature rise or the power consumed, at the sort of pressure differential you can expect from the fan.

Broadly speaking,  throttling the flow to half its unthrottled value will halve the power consumed. The "volume to power" ratio is constant.

With 425 watts absorbed, the fan probably represents a fair chunk of the output of the generator it is intended to cool. It may be worth considering a speed controller instead.

The "fan laws" give the relationship between flow, pressure, absorbed power and fan speed for any given fan.
Flow varies with the fan speed.
Pressure varies with the square of the fan speed.
Power varies with the cube of the fan speed.

If your fan uses 425 watts at maximum flow, it will use 212 watts when throttled to half flow.
It would only use 53 watts if the speed (and therefore flow) were halved.

The cube relationship between speed and power means that very little torque is needed at low speeds, so a very cheap, simple speed controller can be used.

Obviously, speed control is an added complication and goes against the KISS philosophy. The simple fan speed controllers may also play merry hell with  power quality from a small generator (I don't know, it would need checking), but if output is tight, it could be worthwhile.

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Everything else / Re: backup power for a sewage pump?
« on: September 19, 2006, 08:40:17 PM »
If you can live with the limited backup time, I'd say this sounds like a job for a UPS. As has been pointed out, you don't need a particularly good waveform, so anything big enough and cheap enough should do fine. I have found that it is usually a lot cheaper to buy a bigger UPS with standard batteries than a smaller UPS with extended runtime batteries, particularly second-hand. A cheap off-line type of at least 1000VA should be fine and would give at least 30 min of pump runtime with a 1/2 HP pump. Back-up time on no load would probably be well over 2 hours. A runtime chart for the APC SmartUPS range can be found at http://www.apc.com/products/runtime_for_extendedruntime.cfm?upsfamily=165

It is some time since I ran a UPS from a generator. We had to use a very expensive on-line type (made by Galatrek in the UK, local for us) with the intelligence to ignore the deviation from a perfect mains-frequency waveform. Trying to run anything else meant that the UPS was in near-permanent battery mode as it saw the frequency changes as the generator speed controller did its thing, interpreted them as mains failures and switched into back-up mode. I understand the APC "smartUPS" range (line interactive), among others, has adjustable sensitivity to allow operation on generators. Limited experience suggests that, while a big improvement, it is not a complete solution. The only testing I did was on a cheap gas-powered generator of about 5 kVA. You may find your generator has better speed control and does not cause a problem.

Personally, I would look for a second-hand smartUPS between 1000 and 2200 VA and take it out of circuit anytime I ran the generator.

If you don't feel you could live with the limited backup time, it is probably worthwhile going with the 12V pump and battery bank, someone suggested. With 12V switches and without the burden of running an inverter, either stand-alone or in a UPS, you would have a potential standby time of weeks without needing a huge battery bank.


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