NB, but practical! DIY generator

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Avocet

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Having just had no power from about 05.00 until now, my thoughts are turning to getting a generator again. Before I do so, however, I was wondering about building something of my own? I don't have enough money to fork out for a nice Honda inverter jobbie, and I'm wary of some of the cheap Chinese things on eBay in case the (what I imagine will be) horribly dirty output trashes any sensitive electronics. I do, however, have an 8hp Honda engine doing nothing and I was wondering about getting a couple of scrap car alternators (or one big one) and driving it (them) from the Honda engine, then having them charging a car battery, and having the car battery supply a big inverter. 2kW should do me. Just enough for an 800W microwave, some lights and the central heating boiler (which is oil-fired).

Would that be a daft idea?
 
It'll work, I used a car alternator on a Briggs 'n Stratton lawnmower engine.

However, those little 2s jobbies are hard to beat for occasional use and the output is pure sine wave. I used mine on a remote jetty for charging and power tools. The 800w microwave is at the top end of their output.
 
Not an entirely daft idea I wouldn't think, but you may have to consider the size of the battery/alternator

2Kw = 166amps at 12v. You can get alternators that can push out that much, but they'll be pricey.
2Kw inverters aren't cheap either.

By the time you cobble together your engine, some sort of fitting for the alternator, a 12v battery and buy an inverter you'd probably spend as much as simply buying a 2kw genny. (cheapest I've seen one is about £450).

But I can see your logic - we (now) have a camper van and I've got a 1Kw inverter onboard - run the engine and take the output from the inverter into home and I can run most things I need in the event of an extended powercut ...
 
See the thread about paralleling alternators.
Running a 2kW inverter is not trivial, that's a lot of current.
You'd be running the alternators flat out.
The current out of the battery would be a heavy demand on it, I think having several batteries might be better?

It's do-able, but you might not want to run the microwave for more than a few minutes, unless you have lots of battery capacity or a highly rated, well cooled alternator...

And that's assuming the inverter is truly up to the job.
 
I have had a similar idea in the past, as the electricity supply in our area was very prone to disruption at one time (8 failures in one year including one of nearly 72 hours.) Fortunately, the power company has improved things in recent years. I also thought on the battery + inverter idea despite the efficiency losses, as I would not need to run the generator overnight to power emergency lighting plus the heating system. I encountered two problems. The first was the need to separate the generator (inverter) and mains supplies as you must not connect your auxiliary supply to the main circuit. To do so would result in you trying to supply your neighbours as well as electrocuting the squad trying to restore power. The second problem was the question raised by a colleague, who was a wizard with electronics, who said that a lot of inverters at that time had an output that was more of a spiked square wave than a sine wave.
 
Wight Dawn said:
I have had a similar idea in the past, as the electricity supply in our area was very prone to disruption at one time (8 failures in one year including one of nearly 72 hours.) Fortunately, the power company has improved things in recent years. I also thought on the battery + inverter idea despite the efficiency losses, as I would not need to run the generator overnight to power emergency lighting plus the heating system. I encountered two problems. The first was the need to separate the generator (inverter) and mains supplies as you must not connect your auxiliary supply to the main circuit. To do so would result in you trying to supply your neighbours as well as electrocuting the squad trying to restore power.
Click to expand...

I have solar panels on my roof, and the feed from them to the mains system doesn’t seem to cause any problems - there's no way of disconnecting the inverter they feed except by a manual switch. Of course, I get paid on the basis that my neighbours will use any current I don't, but the problem of the system remaining "live" doesn't seem to arise. Within the house, the Consumer Unit is plastered with warnings to electricians that switching off the mains does NOT render the system entirely safe!
 
I've heard of some people plugging their inverters into their home circuits - not a good idea unless you isolate the incoming supply first!
Square wave inverters are cheaper and can run most things. But there are some cheaper pure sinewave inverters around now.

TBH, what's important at home?
For us it's hot water, heating and freezer. We can use candles and torches for light. We have a wood burner if it's just chilly, but despite being gas fired, our hot water and heating rely on electricity. The hob is on gas so that's not an issue. The Freezer would require external power if the power has been off for a long time. The rest can wait.
As we have the m/home at home now we could just move into that ... complete with gas fired hot water and diesel webasto heating! :)
 
AntarcticPilot said:
I have solar panels on my roof, and the feed from them to the mains system doesn’t seem to cause any problems - there's no way of disconnecting the inverter they feed except by a manual switch. Of course, I get paid on the basis that my neighbours will use any current I don't, but the problem of the system remaining "live" doesn't seem to arise. Within the house, the Consumer Unit is plastered with warnings to electricians that switching off the mains does NOT render the system entirely safe!
Click to expand...

But do they supply your house with mains when there is a powercut?
They must have thought about the issues of backfeed and as your inverter will have to sync with the grid I would think that if there's a powercut then your inverter will cut out too.
 
fireball said:
But do they supply your house with mains when there is a powercut?
They must have thought about the issues of backfeed and as your inverter will have to sync with the grid I would think that if there's a powercut then your inverter will cut out too.
Click to expand...

Your fears are groundless - of course if you have a power-cut after dark you'll have no electricity like everyone else.
 
I bought a used Kawasaki 1400w gennie for 175 quid. Keep it in the garage it runs on 2 year old fuel ans is light enough to take to boatyard in winter.
 
Thanks all. I already have several alternators from scrap cars - typically 60 - 80 Amp, but yes, I'd have to parallel them, so I'll have a look at that alternator thread. There's definitely no question of trying to plug into the ring main for the house. Last time this happened we were without power between Christmas and New Year for nearly 3 days and had to throw food out. This time, it was "only" about 10 hours. I'd really only want to run the boiler (a few hundred watts for the pump and fan), the freezer and fridges, and some lights. Microwave use would be very occasional and we have a camping stove too. That would mean inverter loadings typically well below 1kW most of the time, and I could easily knock off a few things immediately prior to starting the microwave.

I work from home a lot of the time, so I need power for my laptop and the router too. In the past ,I've been worried about damaging them, so we have a very small pure sinewave inverter to run them from one of two lead acid batteries and then I just use a cheap Halfords battery charger (which would be powered from the generator) to charge whichever one isn't feeding the "nice" inverter at the time.

It's true I'd have to get hold of a relatively big battery to act as a "buffer", but presumably I could use a relatively unhealthy large car battery from (say) a scrap diesel car - it wouldn't have to be a deep-cycle one or anything like that, would it?
 
Hmmmm. Must admit that's a tempting price...

Of course... I wouldn't get the same satisfaction as I'd get by using up some of the junk Mrs. Avocet constantly berates me for hoarding...

...but I suppose I might get more electricity...
 
AntarcticPilot said:
I have solar panels on my roof, and the feed from them to the mains system doesn’t seem to cause any problems - there's no way of disconnecting the inverter they feed except by a manual switch. Of course, I get paid on the basis that my neighbours will use any current I don't, but the problem of the system remaining "live" doesn't seem to arise. Within the house, the Consumer Unit is plastered with warnings to electricians that switching off the mains does NOT render the system entirely safe!
Click to expand...
Solar panel inverters are designed to shut down in the event of a mains failure because they need the mains input to be able to synchronise frequencies as well as protection for electricity board workers.
 
lumphammer said:
Solar panel inverters are designed to shut down in the event of a mains failure because they need the mains input to be able to synchronise frequencies as well as protection for electricity board workers.
Click to expand...

Indeed, they are generally 'grid tie inverters' which sync to the grid.
It makes them simpler in design, as the grid stops them producing too many volts.
There are solar inverters that will run standalone though.
 
lw395 said:
See the thread about paralleling alternators.
Running a 2kW inverter is not trivial, that's a lot of current.
You'd be running the alternators flat out.
The current out of the battery would be a heavy demand on it, I think having several batteries might be better?

It's do-able, but you might not want to run the microwave for more than a few minutes, unless you have lots of battery capacity or a highly rated, well cooled alternator...

And that's assuming the inverter is truly up to the job.
Click to expand...

Was this the tread you referred to on paralleling alternators?

http://www.ybw.com/forums/showthrea...Cable-and-Sterling-Charger&highlight=parallel

I've tried a search, but it doesn't seem that recent?
 
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