Need portable power supply for diesel glow plugs

[filonic]

Hello,
I am working on a project that requires powering a diesel engine glow plug from a relatively portable power source.  The diesel glow plugs come in a variety of voltages, most common are 6v, 12v, and 24v.  From what I understand, the most commonly found ones are 12v and draw around 10 amps.  I have tried a number of configurations with varying success and at this point I am pretty frustrated with the trial and error method and so I am here to ask for help.  I have been successful using a small 12v lawnmower battery(capacity unknown) with the 12v glow plugs, but it is WAY too big and heavy for my intended use.  When I tried hooking up the same 12v glow plug to a series of 8 x D cell batteries, I was able to achieve a glow, but it seemed to be nowhere near its full heat potential.  I am going right now to buy a 6v glow plug in the hopes that by using the lower voltage, I will be able to supply enough current with the 8 x D batteries.  The power sources I have already purchased that may work include: 

1.  1 X 12v Lead Acid Lawnmower battery (way too large) http://www.oreillyauto.com/site/c/detail/SSB0/U1L/N0057.oap?ck=Search_N0057_-1_-1&pt=N0057&ppt=C0218

2.  8 X D cell alkaline batteries and various holders for different configurations 

3.  1 X 6v 4500mah Lead Acid Alarm System Battery

4.  1 X 7.2V 2000mah NiCad Battery

Obviously I am lost and have no idea what I am doing, so any kind of help would be much appreciated.  The priorities are as follows:

1.  HOT -  it must reach full heating potential which is a glowing orange almost white hot.

2.  Speed - it must reach that temperature in a relatively short time window, less than 20 seconds, by design these plugs are supposed to be fully hot at 5-10 seconds.

3.  Size  -  I really need this to be portable, if it takes a car battery to do it, then its not going to work.  I would like to keep the power source smaller in volume than a 12oz can of soda.  If it could fit in a large pocket, that would be even better.

4.  Capacity -  It will need to be able to bring the glow plugs to full heat and maintain that heat for approx 10-15 seconds at a time.  I am hoping to be able to complete at least 30-50 of these heating cycles before the power source is depleted.

5.  Rechargeability  -  Preferably, it will use a power source that is rechargeable, however if the cost is too much or it will substantially increase the bulk to use a rechargeable power source, using disposable alkalines or nimh is a possibility, theoretically even a disposable 6v lantern battery could work.

I really appreciate any and all input that you guys can give me!

Thanks Alot,
-Alex

[Hero999]

You need batteries with a high enough energy density. Reducing the voltage will do nothing, read up on Ohm's law, for a given amount of power (in this case heat), the current will need to increase proportionally, if the voltage is lowered.

In your case, each glow plug requires 120W and you want it to last for 15x50 seconds, so the battery needs to be able to store at least 120x15x50 = 900kJ of energy.

Simply put, a 1Ah 1V battery can provide 1A@1V for an hour which is 60x60 seconds, E = 1x60x60 = 3.6kJ. In reality, it's much more complicated, the voltage would drop as a real battery discharges, many batteries only deliver a fraction of their Ah rating at high currents and some batteries can't be fully discharged without being damaged, so you'll need a far greater Ah rating than the theoretical value,

[filonic]

Thanks very much for the info.  What about increasing the voltage to 24v and using 24v glow plugs, would that work?  Like maybe 16 sub-c's in series for a power supply?
Thanks
-Alex

[Hero999]

What's the Ah rating of the batteries, at the current drawn by the glow plugs?

You do the calculations.