6Ah to 9Ah is a wide range; you can define the nominal duration by referring to the discharge graphs in the battery data sheet. The glow plugs require 1.5V at 3A not 1.2V. The OP is not asking about ground starting if that is what you are describing.
The starting battery and on-board battery are two separate things. Once again, the plugs are 1.5V at 3A, not 1.2V at 2.4A. The former corresponds to only 2.88W instead of 4.5W which would greatly decrease the effectiveness of the plugs, especially when saturated with fuel/oil.
All batteries behave differently, but the number of charge discharge cycles to reach absolute full capacity is little more than a very minor inconvenience. Besides which, NiCad batteries have some awkward characteristics of their own including the need to attain full capacity. They are also extremely heavy.
This is not correct. The plugs take 3A each as stated by the OP. 7 * 3A= 21A
What specific batteries are you talking about? 7.8 Ah to 9.6Ah is a wide range.
The on board plug power is not required for starting
This is another Ah range. NiCd does not supply 1.5V. Also six 1.5Ah NiCad batteries (if that is what you are talking about) would be costly, bulky and, worse still, very heavy, bearing in mind that they would be inside the plane. Take an example. The weight of a 3Ah LiIon battery is 48 grams. The weight of a 3Ah NiCad battery is 86 grams, but you would need three NICad batteries to equal the energy of one LiIon battery, giving a total weight of 3* 86 grams= 258 grams ie 5.375 times heavier, and this is not mentioning the bulk which would be greater by a factor of 4.43.
. the plugs seem to have individual wires and must be bought together to the 1.5v supply somewhere (for starting ) in flight would a 7 pole rotary switch ( mechanical or electronic) work? just cycle (step ) through 1-7 connections. just need one 1.5v 3A battery .View attachment 99828
As an interested observer ...
If used with a two serial plug approach and single LI Ion cell, it would only mean a four way mux switching 3A. This would also have the advantage that two plugs would be energized for each pulse.
Seven plugs will do pairs with dummy plug resistor as stated on previous post. Glow plugs take some time to heat, so too quick a scan won't do. I don't think 48 grams will be a problem.
spec , that has answered a mystery I have had for 55 years , ... I built a Cesna 127 balsa and tissue , 36" wig span with a .049 glow , but to make it look like the real thing I mounted engine upside down ! , it was a really good looking model , second flight after some balancing etc in my uncles field , engine running well ( I think they lean out in flight) launched into wind , 2 ch 27mhz working OK , engine slowly lost power, wind took it back down hill , loosing altitude 20 ft > 2 ft , crashed headlong into field 5 barred iron gate....
the RC got built into a boat !spec , that has answered a mystery I have had for 55 years , ... I built a Cesna 127 balsa and tissue , 36" wig span with a .049 glow , but to make it look like the real thing I mounted engine upside down ! , it was a really good looking model , second flight after some balancing etc in my uncles field , engine running well ( I think they lean out in flight) launched into wind , 2 ch 27mhz working OK , engine slowly lost power, wind took it back down hill , loosing altitude 20 ft > 2 ft , crashed headlong into field 5 barred iron gate....
sopwith.. sorry to mess your thread..
. On my left hand index finger I still have about four scars from deep razor blade accidents while whittling balsa wood.
Seem to remember I had a wet 2v lead acid cell for the glow plug , had to watch the red and black crock clips didn't touchNever did get the engine to work well. It was always a pain to start.
, my worst disaster was a large balsa Gypsy Moth powered by about 8 feet of 1/4" rubber , wound up with a hand drill ( egg whisk style) , 100 or so turns great,,,, My kid go chasing after it... "more turns Dad .." at 400+ little peg in tail holding, said elastic, shot from one end to other taking all the spars with it ... we nearly cried ....Seem to remember I had a wet 2v lead acid cell for the glow plug , had to watch the red and black crock clips didn't touch
bump
Hy Reloadron,
I am having trouble relating your post to the OP's post.
6Ah to 9Ah is a wide range; you can define the nominal duration by referring to the discharge graphs in the battery data sheet. The glow plugs require 1.5V at 3A not 1.2V. The OP is not asking about ground starting if that is what you are describing.
The starting battery and on-board battery are two separate things. Once again, the plugs are 1.5V at 3A, not 1.2V at 2.4A. The former corresponds to only 2.88W instead of 4.5W which would greatly decrease the effectiveness of the plugs, especially when saturated with fuel/oil.
All batteries behave differently, but the number of charge discharge cycles to reach absolute full capacity is little more than a very minor inconvenience. Besides which, NiCad batteries have some awkward characteristics of their own including the need to attain full capacity. They are also extremely heavy.
This is not correct. The plugs take 3A each as stated by the OP. 7 * 3A= 21A
What specific batteries are you talking about? 7.8 Ah to 9.6Ah is a wide range.
The on board plug power is not required for starting
So there is an off the shelf solution. What is the size, weight, and cost?
Agree, but the critical item is the switch to turn the high current on. A relay to switch 12A at 3.6V or 21A at 1.5V in a small size with a reasonable coil drive does not exist, as far as I can tell. The alternative is to use MOSFETs as the switch which will take a bit of sorting. Heavy gauge, high temperature wire (silicon sleeve/silver coated multi strand conductors) will also be required. It would be better to fit the connector away from the prop for obvious reasons.
At the high currents required the connector choice will be critically important to ensure a low voltage drop and long life. The contact material, like any relay contact, will be a challenge, not only because of the high current, but also because of the low voltage. Being DC doesn't help either.
This is another Ah range. NiCd does not supply 1.5V. Also six 1.5Ah NiCad batteries (if that is what you are talking about) would be costly, bulky and, worse still, very heavy, bearing in mind that they would be inside the plane. Take an example. The weight of a 3Ah LiIon battery is 48 grams. The weight of a 3Ah NiCad battery is 86 grams, but you would need three NICad batteries to equal the energy of one LiIon battery, giving a total weight of 3* 86 grams= 258 grams ie 5.375 times heavier, and this is not mentioning the bulk which would be greater by a factor of 4.43.
Thoughout your post you do not say what specific batteries are being described. The battery model make a big difference to the performance and you seem to have missed the point that the OP wants a light weight, short duration (5min) on board system, not 30 minutes. But even so, LiIon would be a much better solution.
In general LiIon batteries are far superior to NiCad- much lighter, much less bulky, and easier to charge (no memory effect or reversal). they also hold their charge better. LiIon is also better for the environment. These are the reasons for the overwhelming move from NiCad to NiMH to LiIon. Although NiCad were better at high currents, the latest generation of LiIon can also source high currents, 35A in the case of one of the Sony LiIon 18650s, for example.
As I have mentioned already, there are a ton of fake batteries around which have a radically poorer performance than the genuine article, especially for high current applications like this. These fake batteries tend to have a sharply falling output voltage as they discharge and they also start with a high internal resistance.
One final point is that it is important to have a good charger with the correct voltage set points. Once again there are a load of rubbish chargers on the market. For good battery life and reasonable capacity it would be best to charge to 4.1V constant current with no topping charge and cutoff at 3.1V on discharge.
spec
PS: I am an aero-modeller too, but mainly sailplane.
The best scale model I ever saw was a from scratch B17 with four glow plug engines. The real thing flew over the sea front, where I live, last year at the annual air show.
