[Ken Currell]

Hi

I have been playing around with different combinations of power panel, starter and glow plug battery combinations. In order to get a light weight yet powerful power source. I want to use Lithium Ion cells from Industrial packs. The cells can usually be scrounged from different sources cheaply.

I have a bunch of 2900 ma E-Moli cells. Fully charged voltage is 4.2 / cell.

Using 4 cells with about the same capacity the initial voltage is usually between 4.1 & 4.2 volts if the cells are good. I don,t want to ruin my power panel so I plan to use a voltage regulator set at 13.2 volts. The power to run the panel should remain constant and be able to easily run the fuel pump and the glow plug.

The wiring will be changed so the banana plugs for the starter will bypass the power panel and go directly to the battery pack (with an inline fuse). The panel itself will be supplied from the voltage regulator.

Has anyone tried this or know a better way to this?

[Cougar429]

Only concern with the voltage regulator is one with enough current capacity to supply your needs. If you only intend to light off a glow plug not so bad, but if you are also running your fuel pump you may want to take a reading as to current draw.

[Spitball]

Hi Ken - I'm wondering why you don't use just three cells??

[Flypaper]

Was wondering the same thing

[Ken Currell]

Originally Posted by Spitball

Hi Ken - I'm wondering why you don't use just three cells??

Some of the objectives of using this pack are:

Reduce the weight of the flight box.
Supply more power (WATTS) to the starter.
Use the same pack for the power panel.
Have sufficient capacity for at least a full day of flying.

The E-moli cells seem to have a fair drop in voltage. Using just 3 cells won't do a very good job on the electric starter. The starter can have a fairly high draw and these particular cells have enough drop under load that the voltage drop is too high with only 3 cells. The output under load for a 3 cell pack is less than 12 volts. Not enough to drive the starter properly on a fair size engine which also causes a low input voltage to the power panel.

Using the 4 cells will greatly improve the output on the starter. I don't think that the pump will draw too much in the way of amps. If the voltage is set a bit higher the amperage drawn by the pump will be lower. The TOTAL watts will be the same but the higher voltage lowers the amps required.

Although these cells are rated at 2900 ma. by the manufacturer it appears that it is just a marketing strategy. The voltage range on these cells runs from 4.2 volts to 2.5 volts. I only test them to 3.0 volts and the capacity readings are all well below 2900 ma.

The 4 cell vs 3cell (single pack) setup also gives better duration. Using only a 3 cell pack would probably require 2 parallel packs of 3 cells to reduce the voltage drop under load to an acceptable level. This would then be 50% heavier than a single 4 cell pack.

[1_AIR_WOLF]

How much weight do you think you are going to save? It seems like an interesting idea.

[Ken Currell]

Originally Posted by 1_AIR_WOLF

How much weight do you think you are going to save? It seems like an interesting idea.

Good question

The weight savings between a standard 12 volt Mallory E1275 gel cell and 4 E-moli 2900 ma cells is:

1855 grams
(1.85 kg.)

or

65.43 oz.
(4.09 lb.)

[Spitball]

Ken, I see your point - my suggestion would be to feed the starter directly as you say and then use one of these new relatively inexpensive (for what they do) little switching supplies that can supply 5Amps (some of them as much as 10Amps) to feed the power panel. They're small and efficient and if you draw more than 5Amps with a glo-plug, there's something wrong with it! Any case, the supply just shuts down and the magic smoke does not come out. A linear regulator, methinks, is unsuitable, even the larger ones.
I've seen suitable ones advertised in the modelling press and the Net that can work off a supply up to nearly 30Volts and with adjustable/switchable outputs. They run cool and their idle current is very low so they can remain on for the whole flying session. They are very stiff supplies too, some actually increasing slightly too with increasing loads to compensate.
Call yours "The Sophisticated Flight-box"!

[Cougar429]

My 2 power panels already fed directly to the starter plugs, so wonder why you would need to mod yours, except to drop down to the voltage required by your sub circuitry in the panel.

I would agree with trying 3 cells first to see if they hold up with the current draw, which is key here. If your cells cannot supply the current, then the only way to increase that is to increase the cell count to compensate. However, your no load voltage starts to get excessive, necessitating the regulator.

I'm looking for the same solution, just for a different problem. I'm tired and annoyed by the restrictions from the starter cable, (ie. short and incredibly cranky in the cold) so have been looking into trying a cordless drill pack direct connected to the starter. Now just have to find one or more surplus 13.8V packs.

[Ken Currell]

Originally Posted by Spitball

Ken, I see your point - my suggestion would be to feed the starter directly as you say and then use one of these new relatively inexpensive (for what they do) little switching supplies that can supply 5Amps (some of them as much as 10Amps) to feed the power panel. They're small and efficient and if you draw more than 5Amps with a glo-plug, there's something wrong with it! Any case, the supply just shuts down and the magic smoke does not come out. A linear regulator, methinks, is unsuitable, even the larger ones.
I've seen suitable ones advertised in the modelling press and the Net that can work off a supply up to nearly 30Volts and with adjustable/switchable outputs. They run cool and their idle current is very low so they can remain on for the whole flying session. They are very stiff supplies too, some actually increasing slightly too with increasing loads to compensate.
Call yours "The Sophisticated Flight-box"!

The easiest way to get around that is to simply put a tap on the third cell
to feed the power panel. These cells can supply up to 20 amps/cell.

The regulator or switching power supply would simply maintain a better balance on the battery pack.

I'll need to see how much power the panel will draw using the fuel pump and the glow driver. Since they are never used together I only need to supply the highest drain on the battery pack.