MAG 85 Resistance?

[FILIPPO]

I have just tryed to see how much is the total resistance of my mag 85...

this is the set up I have:

mag 3D (black body)
fivemega 9AA to 3D adapter
9 energizer made in japan AAs (elites 1700 coming....)
KIU socket
tali spring fixed with 1mm wire
as well WA1185...

with battery set at 11.8V, have found that Volt at bulb pins was 10.5 so

Vapp= Vbatt - [( RES*Ah)/1000]

10.50=11.8- [3.28X]/1000
10.50=11.8-0.00328X
0.00328X=1.3 Resistance: 396.34 miliohm that's alot!!!

have I done something wrong?
it seems to be so much...how much resistance do you have on your flashlight?
thanks in advance.

 

[rizky_p]

I think you should try running the bulb directly to your battery pack with thick cable and measure the Vbulb there then compares to the Vbulb running with mag body to get the Vdrop. I think that will elimitane additional voltage drop coused by the bulb load and battery resistance.

this formula should be easier to work with.
Resistance = (Vdrop / A) * 1000

That is what i think i am not an expert though....

Thanks..

 

[Mr Happy]

Resistance: 396.34 miliohm that's alot!!!

On the contrary, I'm very suspicious of that number -- it may even be too small!

Your test protocol includes the internal resistance of the battery, and you have 9 cells there. 396/9 = 44 milliohms per cell, not including any other resistance in the circuit. An internal resistance of 44 milliohms is what the best LSD cells like Eneloops can achieve and is lower than ordinary cells. If your result is correct, it is very good.

 

[EvilLithiumMan]

Sounds at least 10x too much resistance. Are you measuring Vbat while the light is on? If not, your readings will be quite misleading.

 

[mdocod]

As previously noted, that test method is including the resistance of all the cells, so it sounds like you are doing pretty good!

 

[FILIPPO]

Sounds at least 10x too much resistance. Are you measuring Vbat while the light is on? If not, your readings will be quite misleading.

no I didn't measured Vbat whaen the light is on...
but I took the higher value I got so the difference between Vbat and Vapp won't change a lot...

If I can find another way to maesure Vbatt and Vapp at the same time I'll do it and post result.

 

[EvilLithiumMan]

If you get a spare charging plug for the Fivemega 9AA to 3D holder, you can connect it's leads to a voltmeter. Turn on the Mag85, then complete the circuit by shorting the negative of the battery holder to the Mag's tube. Now your measuring Vbatt while the light is on.

By the way, the CBP Elite 1700 can deliver 1.1 volts at 30 amps. Had it's internal resistance been 40 milliohms, the drop from IR alone would be 30 X .040 = 1.2volts. Clearly the Elite 1700 IR must be in the 4 to 8 milliohm range. I have been unable to find a figure for the Energizers. I'll bet SilverFox has a good idea of what it is, considering all the NiMH testing he has done.
http://www.candlepowerforums.com/vb/showthread.php?t=79302

 

[Mr Happy]

I have measured the internal resistance of Eneloops in the 40-50 milliohms range, and of Kodak Pre-Charged cells in the 100-110 milliohms range. I have not measured any regular non-LSD cells, but I suspect they are in the 100 milliohms range too.

Those Elite 1700s are pretty impressive cells! Mind you, at 30 amps I don't figure you would get more than 3 minutes run time. I imagine a lower rate is more practical...?

 

[FILIPPO]

If you get a spare charging plug for the Fivemega 9AA to 3D holder, you can connect it's leads to a voltmeter. Turn on the Mag85, then complete the circuit by shorting the negative of the battery holder to the Mag's tube. Now your measuring Vbatt while the light is on.

I think in that way I'll exclude the resistance of spring/tail cap...

 

[Mr Happy]

What I do is take the batteries out and put them in a charging clamp or something, so I can measure the resistance of the batteries alone.

Then I put the batteries in the light and measure the total circuit resistance including batteries like you did.

I subtract the one from the other, and the resistance left over is the circuit resistance of the just the light.

 

[EvilLithiumMan]

I think in that way I'll exclude the resistance of spring/tail cap...

That's true, but you did a good job of reducing tailcap spring resistance. If it's resistance is in the 3 to 4 milliohm range, which I suspect it is, the drop is just a little over 1/100th of a volt. Not much influence compared to the rest of the circuit.

 

[299792458m/s]

I'm kind of new here, but...that seems like really good resistance. I have a couple of 85's and I'm positive that my resistance is much higher than that. :mecry:

 

[FILIPPO]

ok...now I know that 400miliohm is not so much...

BUT! if you put this value in the famouse hotrater you can see that a mag 85 hot of the charger with 12,6 Vbatt put 900L out of the front...not really what I expected...:ironic:

for example some people told me that you cannot run bulbs as O-64430 with 9 batteries...I think it isn't true at all...@ 7,62 Ah of drow with 12,6 Vbatt you will have 9.55V at bulb pins and this bulb (as luxluthor tested:thumbsup instaflash at about 10,9V.:duh2:

have I missed something?:candle:

 

[LuxLuthor]

I just measured resistance of 3 single batteries:

• Eneloop AA - 46mΩ

• Elite 1700 AA (CBP) - 28mΩ

• Elite 1500 2/3A (CBP) - 25mΩ

 

[FILIPPO]

I just measured resistance of 3 single batteries:

• Eneloop AA - 46mΩ

• Elite 1700 AA (CBP) - 28mΩ

• Elite 1500 2/3A (CBP) - 25mΩ

thanks LUX!:twothumbs


...please can someone tell me if anyone has tryed running bulbs like O64430 with 9 cells??


thanks

 

[rizky_p]

I just measured resistance of 3 single batteries:

• Eneloop AA - 46mΩ

• Elite 1700 AA (CBP) - 28mΩ

• Elite 1500 2/3A (CBP) - 25mΩ

Nice to see real figures, i wonder where Sanyo 2700 and Elite SC stands?

 

[LuxLuthor]

Keep in mind, and confirmed with feedback from Silverfox, that internal resistance ("IR") of cells varies widely based upon condition, state of charge, temperature (when hot off charger you will see lower resistance), and load placed on cell. IR therefore should not be seen as a "set number," but rather a range of values reflecting the variations.

My readings were using the "DC Load Test" Ohm's Law formula listed on top of the 1st graph box at this Battery University link with cells that were cold and my estimate of halfway charged cells. I measured mV with calibrated 0.5 & 1.0 amps applied for 5-10 seconds to get my readings with that formula:

​

Some battey manufacturer/retailers can give you a falsely low IR specification, because they measured it hot off the charger...banking on no one realizing how they chose the isolated, best time to test.

 

[FILIPPO]

...please can someone tell me if anyone has tryed running bulbs like O64430 with 9 cells??

anyone?:mecry:

 

[Mr Happy]

...please can someone tell me if anyone has tryed running bulbs like O64430 with 9 cells??

anyone?

Well I haven't tried it, but it seems like a promising idea, so let's look at this.

Osram 64430: 6 V 35 W, axial filament, nominal 4000 hour life.

Firstly, I have read somewhere that the expected bulb life is inversely proportional to the twelfth power of the voltage. So if we increase the voltage from 6 V to 9 V, we might expect the life to be reduced from 4000 to 4000 / (1.5^12) or 30 hours. That seems reasonable for a flashlight, and there's a good chance it will run at that voltage without instaflashing.

Now at the nominal rating the bulb current will be 35/6 = 6 amps. If we up the voltage to 9 V I would expect the current to increase by about 20% or 6 x 1.2 = 7.2 amps.

It means you will need a battery pack that can deliver 9 V, 7.2 A at the bulb. That seems a bit beyond regular AA cells; you might need those special Elite 1600s, or a different battery size like sub-C for example. Depending on battery choice and circuit resistance you might want to stop at 8 cells. 9 could be pushing it.