Portable Generators and sound levels

[Chris Marshall]

I am considering a portable generator as a better investment than a stack of LiPos to acheive an afternoon's flying. It seems to me that I would be better off with just one or two packs per model and expect to lifetime them in a season, rather than a pile that I will not exhaust in a couple of years, after which time they will be deteriorating regardless of use. There is a vast selection available from several manufacturers, with a huge range of prices. Just as important there is a huge range of noise levels from barely audible to higher than the BMFA limit for model engines! The quietest seem to be significantly more expensive.

I would be interested in anyone's practical experience with a generator, both in terms of reliability etc, but also in terms of the noise level of the model they have, and it's perceived acceptability by others. One of the clubs I fly at is electric only because of noise considerations, obviously there is little point in turning up with something as loud as an IC model!

I don't need an explanation of decibels etc, I am just interested in anyone's practical experiences, obviously I don't want to spend more than I need to. Clearly some units are really only any use for a building site with relatively high noise levels, but I am hoping that I don't need the most expensive.

[Phil 9]

the generators I have used or seen have been as loud or in most cases louder than an IC model and would not be good for a noise sensitive site

Or club has installed a charging station that is made up from 12v batteries that are charged form solar pannels

I tend to go for the option of buying enough lipos for 4 flights and can get a couple more by charging from my car battery

[Simon Chaddock]

Be careful.

Most of the generators carry a warning not to use the 250V output with electronic components (LiPo charger?) as the AC wave form is poor. If you ran the generator 12V DC output through a car battery it would be fine.

As the generator is on the ground its sound will not carry nearly as far as a plane in the air.

[Biggles' Elder Brother - Moderator]

Chris,

why a generator? Why not just use a 60-70 Ah lead-acid leisure battery. Its cheaper to buy and run, delivers the same thing - ie multiple Lipo use during one flying session - and, most significantly in your case, its silent!

BEB

[Chris Marshall]

Simon,

The 12V output from most generators are low power although your suggestion would clean up the power suitably it would mean only about 10% of the generator's capacity was being used. I agree that some of the cheaper generators are not suitable for electronics but those with an inverter generally are. Unfortunately again they are more expensive.

BEB,

I already have a leisure battery, but it ran out before I had finished flying the other day. I am considering getting a second as an alternative to a generator, as they are a lot cheaper than what it looks like I will need to pay. But they have a finite life, I don't know what it is likely to be for this sort of usage. One positive thing is that they can be kept fully charged ready to go- in fact that is the best storage condition for them. I think that the capacity of the one I have which is about 5 years old may be reduced, I'll have to measure it.

I am using relatively large packs 4S 5AHr x2 per flight for my helicopter and 5S 5AHr for fixed wing. I may get a 700 size helicopter next year or convert one of my nitro machines so will be into even bigger batteries.

I am still weighing up the pros and cons of each option, and as I said I was interested in the experiences of anyone who has gone the generator route. I beleive that most F3C competition pilots and possibly 3D as well are now flying electric and a generator is the only practical option for them. Their situation is slightly different in that for a weekend or three or four days competition with no access to mains power they would need a boot full of leisure batteries, but it seems to me that it would be a one off investment, as long as it is looked after and maintained properly.

Phil,

your club charging station sounds ideal. The club that I really need this for is a small invitation only one, with only four members, which is where I can get a lot of flights in in one day, but such a set-up as yours is unlikely in the near future. It is not noise sensitive, so maybe I restrict flying to IC there for now.

Ultimately I want to move to all electric for helicopters and petrol for fixed wing. The noise snesitive site may drop out of the equation as I am not sure i will continue there for other unconnected reasons.

[Biggles' Elder Brother - Moderator]

Yes Chris - you have a point. Once you go to bigger packs the Leisure Battery solution starts to take a hammering. A 5s 5000mAh battery will take approximately 8Ah out of a 12 volt battery to charge. So assuming, say a 70Ah leisure battery, and you don't want to take it below 30% capacity then you can't take more than about 50 Ah out of it, then that's just 6 charges. You'll lose a bit on inefficiency, but you'll gain a bit on the fact that Lipo's won't be completely flat - so that probably a fair estimate.

I suppose it depends on how many batteries you have and how much you want to fly in one day. For example I have four 6s 4000mA - from my leisure battery that gives me upto 9 flights on one leisure battery charge - which I find is enough. But its a personal thing of course and 4 6s 4000mAh batteries aren't exactly cheap!

BEB

[Alan Randall]

I don't know a lot about it, but from some guys who use them to charge lipos at our model shows, I belive you need a sine wave generator. This appears to do the trick as it claims to be suitable for clean power for lap tops etc.

[Chris Marshall]

That's the sort odf thing, but it's noise figure is 7dB at 1/4 power over this: **LINK** when running at ful power. I'm guessing that at full power it's probably approaching 20dB which is about four times as loud. Hence my original question of what are people's practical experiences of acceptable noise levels.

[Former Member]

[This posting has been removed]

[Phil 9]

Posted by Chris Marshall

I already have a leisure battery, but it ran out before I had finished flying the other day. I am considering getting a second as an alternative to a generator, as they are a lot cheaper than what it looks like I will need to pay. But they have a finite life,

.

The biggest short fall of electric power from batteries they do have a finite life

[Chris Marshall]

Tom,

which model is it please? "whisper quiet" sounds like a good baseline to start from.

[Former Member]

[This posting has been removed]

[Paul Adams]

Why purchase and lug about a generator, when you have probably driven there in a vehicle with an engine, 12V charger circuit and you can sit inside with the heater on during the winter (or air conditioning if the summer if the sun ever does come out).

My suggestion would therefore be to use a 12V charger connected to the car battery, then after a couple of charges, run the engine for 30 mins to recharge the battery. All self contained, quite and low electrical noise. It would probably use less fuel than running a generator constantly and by the time you have got home the car battery would be fully charged.

Edited By Paul Adams on 05/11/2012 23:55:52

[Chris Marshall]

Paul,

I have considered that, but have not yet investigated it. I think it would depend on the capability of the alternator to produce significant current with the engine idling, as I don't think it would be acceptable to sit there revving the engine for 30 mins. I think that it would almost certainly consume more fuel than a generator for the same power, but it may still be an acceptable level. The information panel in my car gives fuel consumption in mpg, but when the car is not moving it switches to giving a reading of volumetric consumption. I've never really taken much notice, but I will have a look tomorrow. I may put a clamp ammeter on the battery lead to determine the recharge rate after partially discharging it, to see how long it actually needs to run to restore charge.

[Ben B]

In-car charging with the car at idle might well not be a good idea. I've seen plenty of cars where they produced little to no charge when idling (in some cases I've found out the hard way by flattening the battery sitting idling with the headlights on).

A generator will increase the throttle to compensate for a drop in voltage, a car idling will not.

Now what I don't understand is why you can't have a silencer that is an exit pipe pointing straight towards a parabolic plate that reflects the sound up into the sky. Kind of like a satellite dish in reverse.

[John Olsen 1]

Well in principle you could, but for the wavelengths involved the dish might need to be pretty big, so it might be just as easy to use the same material in a more conventional way.

One idea that works well for fixed generator plant is a 44 gallon drum buried in the ground with a pipe going in and another one coming out.

John

[Frank Skilbeck]

And to make every one sick, I've just come back from a business trips to the US and visited a model flying site there, tarmac runway plus covered pits area with benches and mains power,

[bushwhackerbob]

Saw these 4 stroke 12v 50amp/hour generators at the recent Malvern caravan show, British designed and produced at a very reasonable price and perfect for charging on the field without the cost of high end generators. They had one running continuously and it was very quiet. It is found at **LINK** The show launch price was £449.

If I eventually go to bigger leccies this is a much better option than using leisure batteries, which are rated usually at around 100amp/hour.

[Peter Beeney]

One of the reasons for using an alternator as apposed to a dynamo, on a modern vehicle, is because it will still deliver the current at tick over speed. The drive pulley is smaller than the crankshaft pulley, and thus will turn faster. So it runs faster than engine speed. The alternator, with the AVR (Automatic Voltage Regulator) controlling it, is essentially a constant voltage source, with unlimited current, up to a point anyway, so it should be able to deliver the current at tick over. The slight problem is that as the battery is charged up it’s voltage rises and therefore the charging current decreases; up to a max voltage of around 14.2 volts and no amps. It’s a bit like charging lipo’s, you can put 90% of the charge in in 10% of the time, the remaining 10% of charge takes 90% of the time!

At a complete guess, I’d think that an alternator will be capable of supplying 150 - 300 amps at any one time. So a series of short runs may be better than than one long one. Also, just as a point of interest, if the ignition light goes out, the alternator is charging.

When I was ‘in the trade’, so to speak, 1980’s, powered gliders were becoming popular, and as I’ve always had a 12V car battery as a field power source, we used this to power the chargers. We’ve always parked the cars close by at the back of the pits area, so I made a pair of long jumper leads, just heavy duty, to carry the charging current, so that I could park the car a little distance away, and still charge the field battery in the pits area. This was just from any intrusive noise point of view. This worked well, and I certainly don’t think I ever noticed any difference in the fuel levels!

We don’t do this now, no demand, but I still have the leads, just in case, and I’ve also always carried standard jump leads, too. It’s very easy to underestimate how much current your charger requires to power it, mine can drag up to 45 amps out of the source at full chat, and in those dim and distant days someone was once left at the field on his own with a flat battery! No phones back then, just a long walk…… So thereafter it was a little unspoken rule that we made sure all engines were running before departure.

Might be worth experimenting with, but from some experience of small gen sets, these can also be very unobtrusive. And this was also back in the past.

Good Luck.

PB

[Chris Marshall]

bushwhackerbob,

That looks very interesting, it is as quiet as the best generator I have found so far and does away with the need for a mains to low vltage converter. I suspect it would probably need a small leisure battery to stabilise the voltage, I remember from my time designing electronic vehicle instruments that a sudden change in load would produce quite a voltage spike from an alternator if there was no path to dump the current. Either that or some big surge suppressors. I will investigate further, thanks.