Don Fry Posted August 2, 2021 Share Posted August 2, 2021 I am not a fan of the PRC. But the last post, assuming that stuff made there, is a fake, when a reassuringly expensive stuff sold in Europe, with no evidence of origin is good, does not further the argument. And, looking at the terms and conditions, the UK provider, as recommended, does a 30 day refund, from Ayesbury? Via China? Quote Link to comment Share on other sites More sharing options...
Nigel R Posted August 3, 2021 Share Posted August 3, 2021 LM388 is an obsolete audio amplifier I think. A typo? Lm338 would be what you need. Plastic package may not be rated for enough current. The big metal can is the one to get. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted August 3, 2021 Share Posted August 3, 2021 For Heaven's Sake! A plug will *automatically* draw the correct amount of current if it is connected to a low impedance supply of the correct VOLTAGE! A high capacity NiMh cell (sub-C, or 3000mAH, NOT AA) will drive both 1.5 AND 2| volt plugs just fine, without the need for complex circuitry - and you will never blow a plug, or worse, overheat one - with it. The resistance of a plug is proportional to its temperature. The higher the temperature, the higher the resistance. This makes the current self-regulating. If a plug is wet, its temperature will be lower, so it will AUTOMATICALLY draw more current until it dries out - provided the supply can deliver the required voltage at the higher current. This is why a single NiMh cell of adequate capacity is ideal. No need for dropper resistors, complex power supplies, or anything. Indeed, dropper resistors just make things worse, as they prevent the plug from drawing the current it needs without human intervention. Putting a 5 amp ammeter in series with the plug will give a lot of information about what is going on in the engine. Not all plugs draw the same amount of current. An OS 8 typically draws just under 3 amps. Some manufacturers draw a bit more, some a bit less. You need to check your plug dry and out of the engine to determine what its "normal" current is. Once back in the engine, if it is drawing more, it is flooded. Just wait until the current drops back a bit and the engine will start. If the current rises when the engine is cranked over, dropping back immediately when you stop cranking, the engine is dry. The cool air being pumped through is cooling the plug, and as soon as you stop blowing cold air over it, it will instantly return to normal. Trying to control the current in a plug (as in a power panel) is the completely wrong thing to do. Give it the right VOLTAGE and it will automatically draw the right current. Furthermore, with a power panel, cranking up the current to dry out a wet plug will overheat the plug when it dries. By the time you have reacted to the increased current and turned it back down, its too late. The damage is done. At best you have shortened its life, and at worst, you've blown it. Keep it simple, and your plugs will last for ever! Well, nearly anyway! ? I've been using the single cell NiCad/NiMh for decades, and I can't remember the last time I blew a plug. -- Pete 2 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted August 3, 2021 Share Posted August 3, 2021 9 minutes ago, Peter Christy said: Trying to control the current in a plug (as in a power panel) is the completely wrong thing to do. Power panels are just PWM choppers to give a full 12V for a user adjustable 10% - 15% duty cycle, are they not? I doubt any are complex enough to truly compensate for plug resistance (such as the RCATs does, but they want $100 for it). Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted August 3, 2021 Share Posted August 3, 2021 1 hour ago, Cassandra said: Anyway, this topic has prompted me to rip the glow starter circuit (which I never use) out of the power panel on my flight box in preparation for fitting an XL4015 based 1.25V supply. If you wish to add unnecessary complication, that is entirely up to you. I like simplicity, as there is less to go wrong, and a decent capacity NiMh in series with an ammeter is about as simple as you can get. -- Pete Quote Link to comment Share on other sites More sharing options...
Martin Dance 1 Posted August 3, 2021 Share Posted August 3, 2021 Having followed this topic for three pages, much of it very interesting, I'll modify my original observation. Have a known good plug in your flight box. At the start of your flying session put plug into glow clip. Plug lights up? Yes. Remove plug from glow clip return it to flight box. Attach glow clip to glow plug/ remote glow clip on model. Start engine and fly ( after removing glow clip from model). Motor doesn't start, refer to my earlier post. Can't get much simpler or reliable. ? Quote Link to comment Share on other sites More sharing options...
Don Fry Posted August 3, 2021 Share Posted August 3, 2021 Trouble is, you are placing a fragile known resistance across a voltage source. A robust resistance might be better. Normally measuring volts or amps is the way to go. A meter is the device that physicists settled on a century or so ago. Ohm’s law. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted August 3, 2021 Share Posted August 3, 2021 I've kept out of this so far, but I feel obliged to say something as it's been going on for a while now. I'm a bloke with a technical background, so I don't mind facing the odd hi-tech challenge to overcome problems I encounter. To be honest, starting a glow engine isn't one of them so I see no need for a hi-tech solution. I connect a sub C powered glow starter, turn the engine over and it normally starts. I had a problem a few years ago with a glow starter with a built in ammeter, which was a bit temperamental. A finger tap or two would spring the meter into life. I swapped it for ones without a meter and have been OK since. I put that down to it being too technical for what was needed - obviously too many failure points. One thing I will say that hasn't been mentioned much. I always charge my glow starters up before each flying session. I see a lot of folk struggling for ages only to reveal that their glow starter hasn't been charged for a while (Duh). Could this be a common problem I wonder? I don't think I've ever had to change a glow plug because the engine wouldn't start. I've given loads of plugs away to people who were struggling to start theirs though. I also find that having horizontally mounted engines can put a bit of strain on the "segments" that open up when the starter is squeezed and grip the plug when released - due to gravity and the large rotational forces involved. This can affect the grip on the plug the next time it is used. Nothing that the occasional strip down, clean and adjustment with a pair of pointed pliers cannot resolve. 1 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted August 3, 2021 Share Posted August 3, 2021 Wot he said. ^ 1 Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 3, 2021 Author Share Posted August 3, 2021 Hi Guys Gary, welcome. You're quite right. This thread has been growing for a while now, but also moving far, far away from my original question. I do notice some posters getting a little hot under the collar about what's being said, and that was certainly not my original intention. Considering asking to moderators to close the thread down. Interested in what's being posted, but not if it's going to upset people. T'aint worth it. Martin Appreciate the thought, but surely that will only check if the glow starter is working. Says nothing about the plug in the motor. Jeff Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 3, 2021 Author Share Posted August 3, 2021 Hi John Wot who said? Jeff Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted August 3, 2021 Share Posted August 3, 2021 Jeff, did you get my mail with the full details? The cheapo ebay LM338K`s work fine, as do the LM338T`s with a heat sink. If you got it do you think that you could copy it onto here please? The circuit I published some years ago showed an incorrect pin out, sorry. Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 3, 2021 Author Share Posted August 3, 2021 Hi Martin Sorry, no sign yet Jeff Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted August 3, 2021 Share Posted August 3, 2021 1 hour ago, Jeffrey Cottrell 2 said: Hi John Wot who said? Jeff Post above Jeff, ^ Quote Link to comment Share on other sites More sharing options...
Martin Dance 1 Posted August 4, 2021 Share Posted August 4, 2021 Jeff, Having eliminated the glow driver as the source of he engines failure to start the problem lies within the model. That probably means gaining access to the engine and fuel tank exactly the situation you wanted to avoid unnecessarily by having a glow driver which indicated the functionality of the plug. Much as I love gadgets as much as the next flyer, they are often not the simplest solution to a problem.? (help my emoji file is playing up) Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted August 4, 2021 Share Posted August 4, 2021 Apologies Jeff, I missed out the 996 bit of your address. You should have it now. Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 4, 2021 Author Share Posted August 4, 2021 6 hours ago, Martin McIntosh said: Apologies Jeff, I missed out the 996 bit of your address. You should have it now. Hi Martin Got the e-mail now, but the circuit diagram seems to have fallen off the perch. Could you have forgotten to attach it? Jeff Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted August 4, 2021 Share Posted August 4, 2021 Hi Jeff, there are three attachments with the diagram and a couple of pics but when I looked at the copy I sent to myself there were none. Just tried again. Stupid internet (or me). Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 4, 2021 Author Share Posted August 4, 2021 Hi Martin Success. Got the e-mail now with attachments. Do you still want me to post the circuit on here? Given how much help you've been to me, I'd vote stupid internet every time. Just to re-inforce that, have a read of my last post on the Excelsior re-furb thread. Jeff Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted August 4, 2021 Share Posted August 4, 2021 The JP glow stick with ammeter arrived today. I put one of my suc C 3800 mAh NiMHs that hadn't been charged for a year. I stuck an old plug into the glow stick and it glowed bright red and the meter went to full scale deflection. The meter is marked 0, 2 and 6 with nothing to say if this is amps or just a scale. So, the glow stick is now on charge and will be used in anger in the not too distant future. I have a second glow stick with another 3800 mAh cell and that will also get a full charge but that also lit the plug. Perhaps replacing the existing sub C of 1800 with a larger one. The 3800 mAh was the largest I could find about 3 years ago. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted August 5, 2021 Share Posted August 5, 2021 If you can copy the whole mail on here it would be great since I don`t know how to do it! Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted August 5, 2021 Share Posted August 5, 2021 I just do not like glow sticks Peter. The cell in the metered one I have is now dead. The only type which seems OK is the twist lock but not seen one for sale and since nearly all of my models have an inverted engine and/or remote connector I much prefer my method. I can always switch to the 1.4V option for a wet plug which helps. Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 5, 2021 Author Share Posted August 5, 2021 Hi All Martin has sent me details of his updated glow driver design, and asked me to post them on here for all to see. So, here we go: Hi Jeff, here is the circuit I use for glowplugs. A few more components are needed to make it work properly than I first said but easily obtained from The Component Shop, the regulator from ebay since the genuine article is now very expensive. I have shown a plastic cased LM338T as well as the large metal one. This is used on the wooden box version and needs the large metal heat sink shown whereas the 338K requires less so. A very low value (2.7 to 4.7 Ohm) resistor can be fitted at point `X` if you want a voltage of more than 1.25V. On the box I have a centre off double pole switch to go between 1.25 and 1.4V but you do not need to go that far. I use a 3s2p NiMh Eneloop or a 1s Lipo. A higher input voltage just makes everything get hot but you could use 12V if you wished. Hope this helps Jeff Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 5, 2021 Author Share Posted August 5, 2021 26 minutes ago, Martin McIntosh said: If you can copy the whole mail on here it would be great since I don`t know how to do it! Hi Peter All done Jeff Quote Link to comment Share on other sites More sharing options...
Jeffrey Cottrell 2 Posted August 5, 2021 Author Share Posted August 5, 2021 Hi Cassandra Quite right. I'm using a 5000 c cell on my home brew, only cost £5 too. Mind you, Peter did say 3 years ago. Things have changed (I've got more grey hairs, for one thing). Jeff Quote Link to comment Share on other sites More sharing options...
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