8xAA NiMH - can you boost to 12V?

I like my modded HID Maglight, but it would be better if i could power it at a full 12 volts. 8 AA NiMH only output a maximum of 9.6-11.4 volts. Comparing my old LC100 using 8 alkaline, the light output was greater at even 11-12 volts.

Is it possible to create a battery pack with an integrated boost circuit to output somewhere near 12V, or am i asking the impossible? Those battery holders in the Group Buy forums look like they could house a boost circuit.

That's not much voltage per cell. How much current are you pulling from them? Have you checked to see if any are dead?

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eluminator said:
That's not much voltage per cell. How much current are you pulling from them? Have you checked to see if any are dead?

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That's plenty normal voltage for NiMH's which are nominally rated at 1.2v per cell (small AA alkalines are rated at 1.5v, but cannot supply enough current to run the HID). Fresh off the charger you get around 1.43-1.46v for new cells, but this drops to around 1.36-1.38v after a few hours rest.

I think it was Sway who said that Rayovac IC3 2000ma cells would only run his M*gHID mod for a few seconds??? Either he had a weak cell or two (likely) or the start-up current requirements for HID are too much for these cells. HID temporarily draws more than 5a to start up the plasma arc.

Perhaps, ask ufozkiller if there is an easy boost circuit mod using EL 3AA-D adapters, on his GB thread?

1. LedAgent, are you running new AA NiMH's of which brand? Some are better at delivering higher voltages (suffer less voltage sag with higher current loads) under loads greater than 1a that the HID requires for constant running.

2. I forget, does the M*gHID mod use the M*g switch (assembly)? If so, you could try cleaning all of your electrical contacts on the M*g, to make sure the ballast is getting enough current. That can make a difference, where/how are you measuring the voltage of the 8 AA NiMH?

Hi there,

A boost circuit would probably be a good idea, so that
when the cells drain down to 1.1v you still get bright
light.

National Semiconductor makes a "Simple Switcher" that
can probably do this quite easy. I'll look up the
number if you cant find it.

Take care,
Al

Any chance you could just get 10 cells in there? I did that in a bunch of my lanterns. Put two packs of 10 cells in parallel, it was just about perfect under load.

I have think about the same idea before.
But I forgot this idea after doing the "ceiling bounce off" runtime test. The lux reading is consistant for mostly 1 hour, then the brightness start to drop until the light flickering at around ~1.5hr. I satisfy with the result.
The voltage sag is not much when draw at ~0.5C and it is good to remind that the Absolute Max. Instantaneous Voltage is 11.8V & the Max. Safe Continuous Operating Voltage is 11.0V. Also, I cant find any space for locating a boost circuit in my HID mag. I am using the FM's 8AA to 2D batt holder in it.

For Mag2HID, you could put the regulator circuit behind the ballast. There's about a 1/4" clearance if you push the ballast toward the lip.

BTW, I just discovered that mine was slightly bored out so even the high capacity Energizer mAh will fit. This means 2hrs+ of runtime. Thanx SilverLegacy

Hi again,

Brock:
Sounds good to me too...i like as simple as possible.
If he can fit two more batteries, or even perhaps
one more battery it could work just good enough.
Good idea!

Take care,
Al

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udaman said:
I think it was Sway who said that Rayovac IC3 2000ma cells would only run his M*gHID mod for a few seconds??? Either he had a weak cell or two (likely) or the start-up current requirements for HID are too much for these cells. HID temporarily draws more than 5a to start up the plasma arc.


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Those were 2100mAh Energizers, guess I had a bad batch others have had good results with them. When warmed up the MINI HID pulls around 1A, the spec sheet says .98 and my DMM reads 1.03.

Later
Kelly

ensig,

thanks~
I may have a try if someone can make these circuits for us /ubbthreads/images/graemlins/grin.gif. Haven't think this before.
In fact, I have already leave 5mm gap between the ballast and switch in there. Also, I have put a 2A fuse in the gap but without knowing what the fuse is used for /ubbthreads/images/graemlins/hahaha.gif. Just read that is recommened by WA in their pdf file.
I am already using the sanyo 2500mAh in my Mag2HID. But I got just over 95mins runtime in the first run. And got only about 65mins with 8x GP2300mAh. /ubbthreads/images/graemlins/icon23.gif I will do the runtime test again when I have time tonight.
Oh, The Mag2HID from the GB already bored out the battery tube for you? Sounds great~

Dear,

I used MAX1771 from MAXIM (with external N channel FET) with 2 series connected Li-Ion which is 7.2V for my bike light adopting 10W HID from Welch Allyn. It worked great so far for more than 2 years.. It should be better with 8 NiMH as the voltage is higher so efficiency becomes better.

Cheers..