Battery+ammeter

[fly boy3]

This could be a silly question, but here goes. As I am dinasor I am still using a 2v lead acid battery for my glow plug. I have now added an ammeter to the circuit. Do I need to remove this meter to charge the battery ? but if not what should it read when on charge ? Cheers

[Denis Watkins]

Take the ammeter out of series for the charge, as you say. There are no benefits to leaving it in the circuit at charging and it would spoil the sensing of a modern charger, it would absorb energy, and if it is a moving coil meter it could be damaged.

An Ammeter could be added to your charger, with a diode, but does need to be sturdy as lead acid can pack a punch

[Martin Harris - Moderator]

Ammeters have very low resistance so no problem charging through one. If it's a centre zero mechanical one, it will show a reading the other way but if not, it will try to deflect backwards. No real problem with a small charge current but could cause possibly mechanical damage if forced against a stop.

Edited By Martin Harris on 29/02/2016 22:19:58

[Shaunie]

I very much doubt if you are a dinosaur, I'm sure many still use them, however many glow plugs such as the Enya No3 are 1.2-1.5V. You are therefore expecting 0.5V to be lost in your glow clip and lead, if not its sayonara to your glow plug. Personally I use a glow stick although I do have a back up in case of a bad tempered engine that refuse to start and runs my glow stick flat, which rarely happens. Bear in mind that the hotter the plug is the more the ignition advance, if your engine are prone to biting back when starting it may be worth dropping the voltage a bit and a glow stick would do this

With regard to the ammeter, if it's a moving iron type it will read charging current, if it's moving coil the needle will go backwards a bit but I doubt if it will be sufficient to do damage to it.

Shaunie.

[fly boy3]

Hi Shaunie, my Cyclon 2v battery died this Winter in my damp shed. It was 25year old. Never blew a plug, but this was probably luck. This week I have just ordered anEnya No3 plug, do not want to blow it. What is the modern equivalent to 6ft leads to drop the volts to safe level of 1.5 volts ? I have a problem when I have used a glow stick, as it does not clamp well unless plug is vertically oriented. Thanks.

[Engine Doctor]

Hi fly Boy 3 . The modern equivalent is a large capacity NiMh instead of the lead acid battery that will power your glow plugs without any fear of blowing them . I converted one of the old MFA glow plugs power packs from Lead acid to NiMh. It has a ammeter to show that glow circuit is ok . This also shows a reverse current when charging . It uses a banana plugs and leads fitted to a conventional glow plug clip . Dead simple and gets charged when needed , usually once a year.

[fly boy3]

Hi ED, I like that idea. Would need something about 2-3Ah ? Sub C cell , would this fill the bill and if so how would I charge it. Cheers

[Peter Beeney]

fb3, I’ve always used a 2V lead acid as a glow driver, back in the early days it was a wet cell, but only because I had access to them. Then the Cyclon SLA came on the scene, the original Hawker Siddeley variety were excellent, I suspect the one you’ve just binned may have been one of these. But the present ones are still pretty good, and I just connect them with a standard length clip-on lead; and, just like you, I’ve never blown a plug, either. Again, way back when I traded with John D Haytree I always used Fox plugs, and they were always labelled 1.5V.

Just for idle tinkering, once upon a time I gathered up a motley collection of 8 different plugs and tested the current flow at 2V. No two were the same, and they varied from 2 amps to 5.1 amps. This means they do rather like a bit of poke so I consider a low resistance source SLA to be a worthwhile investment. Then I left one connected in the clip for half an hour, just to see what would happen; it was still glowing bright orange, (8Ah cell), which is what I like to see. By this time the clip was almost glowing, too! Actually, this is probably the worst case, when the plug is tightened in the cylinder head this must act like a heat sink and therefor the plug element is only ever going to be slightly cooler. Over the years my glow clip has also started other pilots sometimes reluctant engines; I think it probably burns any neat fuel and oil residue off the element fairly smartly…

I simply charge mine with the standard lipo charger, although set to lead acid of course, but particularly in the winter I occasionally raise the voltage to about 2.6V for a while with my bench supply unit to insure it’s kept well fed. SLA cells do tend to show a noticeable dislike to being kept for long periods in a discharge state; but I guess you already know this anyway. If you had 2.3V supply you could keep it permanently ‘floating’ across this, it keeps it in really good nick.

Good Luck with whatever you do in the way of a glow driver…

P B

[jrman]

+1 for Cyclon cell with standard length clip on glow lead. I have also been using this set up since Cyclons became available (mid 70's?) and have never blown a plug. (Have I tempted fate?)

[Engine Doctor]

Hi you can use a couple of 3000 Mah in parrallel or buy a"D" cell at 4000 plus mah They will run a glow plug for ages before they need charging. Any normal charger set to NiMh will charge it ok. Just looked on eBay and 7 dayshop com sell two 4000 may ready NiMh "D" CELLS for under £7. Put them in parallel and you will have 8000 may and they won't self discharge .They will be fine on all plugs with no chance of blowing them.

[fly boy3]

Hi ED, those D cells look the bees knees to me. Could I use my 2volt Cyclon battery charger on them ? Thanks to al l for very interesting input. Cheers

[Engine Doctor]

Do you know the out put of the charger ?

[fly boy3]

Quite small, 2v, 400. MA max. Cheers

[Shaunie]

Hi FB3,

I just use a conventional glow stick, it's a Rip max one IIRC. It's fine for an afternoons flying often two, the only time I have a problem is with a very reluctant engine that needs loads of cranking to start. As this is a rare occurrence it's not often a problem. I have another one, can't remember the brand, but it unscrews so the sub-C can be replaced. They stay on with inverted engines, if they start to fall off then I gently tap the claws over with a hammer until they grip again.

I used a 2v cell when I was younger and blew loads of Cox 0.49 glow heads until I worked out what the problem was!

Shaunie.

[Geoff S]

I used to use a glow stick but I wasn't keen on that heavy thing hanging on the engine, often not very firmly, and close to the propeller. It always looked like an accident ready to happen. I made up a box with a Cyclon battery and ammeter so I could connect to the plug with a much lighter lead. Actually, the voltage isn't all that important - it's the current that may blow the element.

Never had any trouble with the Cyclon blowing plugs but I did have quite a lot of wire inside the box to limit the current. I charged the Cyclon with a constant current (one of the charge options in the data sheet) from the NiCAD section of my charger. Cyclons are excellent voltage sources. I used to fit 3 in a cycle drinking bottle in a cage on my bike for winter commuting and charged them at work with a bench power supply I hid away to stop anyone else using it for more legitimate purposes.

Geoff

[Shaunie]

Hmmm, accident waiting to happen? So three feet of dangling umbilical cable at risk of getting wound up in the prop isn't? I decided that a glow stick as a single self-contained unit that is likely to just drop on ground due to its weight is on balance probably safer.

Geoff S, why is voltage not important? The load is resistive ( apart from a slight adjustment for temperature coefficient of the element) as a result it is the Voltage that forces the current, therefore more Voltage equals more current.

Shaunie.

Edit for typo.

Edited By Shaunie on 01/03/2016 22:19:24

[Geoff S]

To a first approximation you're right of course but it's the I^2R that heats the element so the thing to monitor carefully is the current.

A light cable can be easily moved back away from the propeller, a heavy glow stick that often isn't all that tight can't. I almost never fly with a glow engine now anyway. In fact I can't remember when I last did. It's electric or petrol these days but I never blew a glow plug with my Cyclon.

Geoff

[Engine Doctor]

Posted by fly boy3 on 01/03/2016 20:23:04:

Quite small, 2v, 400. MA max. Cheers

Hi Flyboy 3

I have sent a PM

[Keith Berriman]

I have used a D size ( 4000 mamp ) rechargeable NIMH cell for ? years with confidence. I also have my own design connection in that I have an old type stereo socket on a small plate bolted onto the undercarriage and hard wired cables one to the plug with a collet ( suitable for plug ) and the other to the exhaust fixing screw. I then have the male stereo plug on the end of a short cable from the battery box which has an ammeter in line to show plug in use. When charging the needle does go backwards when charging with no problem.

[Shaunie]

Posted by Geoff Sleath on 01/03/2016 22:35:46:

To a first approximation you're right of course but it's the I^2R that heats the element so the thing to monitor carefully is the current.

It's also V2/R.

But without V you can have no I. Set V correctly and I will take care of itself. Start off with too much V and attempting to control I by having a resistive lead is a recipe for disaster, use a lower current plug and the voltage is instantly too high and the plug blows.

The resistance of the element has a positive temperature coefficient which will tend towards a constant current effect, terminating of course when the element gets so hot it melts.

Monitor the current but set the voltage.

Shaunie.