D lithium question

[Metatron]

hi folks i have a few D lithiums lying around brand new, nailbender has made a sst-50 drop in for me direct drive, now when testing draw i only get 1.8 at the tail. same test using AW's 18650's i get a reading of 2 amp at the tail.

if the D's are rated at 4.5 mah why am i only getting 1.8?

cheers

steve

 

[mudman cj]

This could be a case of the D cells holding voltage better under load than the smaller 18650s or the D cells are charged to a higher resting voltage than the 18650s or a combination of both.

Let's say they are both charged to 4.20V resting but the 18650s sag under 2 amps to 3.6V. The power drawn from them is then 2*3.6=7.2 Watts. If the same power were drawn from the D cells at 1.8 amps, then that would require them to hold 4.0V because 7.2/1.8=4. This is not out of the question, and becomes more reasonable if the D cells are charged slightly more than the 18650s.

 

[Metatron]

ty for that, i was just under the assumption that a cell rated at 2.2 would give me that power and one rated at 4.5 would also give me that, and in saying that i have a 18650 pushing an o light st-50 at 3.4 so im totally confused as to what to expect from cells.

 

[KiwiMark]

The power draw is related to Voltage and Resistance (v=i/r) - nothing to do with capacity. If the resistance of the cell or protection circuit is higher than the amps will be lower. If the voltage holds up to a higher amount then the amps will be higher.

4.5Ah cells can supply 2.2A for a couple of hours.
2.2Ah cells can supply 2.2A for about an hour.
Therefore the big advantage of the D cell Li-ion cells is that they can do what the smaller cells can do, but for longer before running out.

 

[Metatron]

The power draw is related to Voltage and Resistance (v=i/r) - nothing to do with capacity. If the resistance of the cell or protection circuit is higher than the amps will be lower. If the voltage holds up to a higher amount then the amps will be higher.

4.5Ah cells can supply 2.2A for a couple of hours.
2.2Ah cells can supply 2.2A for about an hour.
Therefore the big advantage of the D cell Li-ion cells is that they can do what the smaller cells can do, but for longer before running out.

thanks for that mate, well ive learnt a bit here, i was hoping i would be able to retire my P7 mag/D, but its heaps brighter than the sst-50 hands down, still not a bad 'get'

steve

 

[tx101]

thanks for that mate, well ive learnt a bit here, i was hoping i would be able to retire my P7 mag/D, but its heaps brighter than the sst-50 hands down, still not a bad 'get'

steve

You can still retire your P7 Mag with the SST-90
I came up with the same problems as you.
I tried an IMR 26500, KD D li-ion and a Plasmaman D li-ion
All three cells gave me a tailcap reading of around 3A

From what I understand resistance is the greatest foe when trying
to reach high currents.
Everything from the cell itself to the thickness of the wire used
in the light will have some resistance

I have just build a Mag SST-90, I was disappointed that I was getting no
where near 9A but the SST-90 is definitely brighter than the P7

Read about the build here

 

[Metatron]

You can still retire your P7 Mag with the SST-90
I came up with the same problems as you.
I tried an IMR 26500, KD D li-ion and a Plasmaman D li-ion
All three cells gave me a tailcap reading of around 3A

From what I understand resistance is the greatest foe when trying
to reach high currents.
Everything from the cell itself to the thickness of the wire used
in the light will have some resistance

I have just build a Mag SST-90, I was disappointed that I was getting no
where near 9A but the SST-90 is definitely brighter than the P7

Read about the build here

g'day mate, read ur thread, very nice indeed, now if i could get a link to that batt that gave u 3.4 i would be up and running! i have the same host as u by the way! i am determined to get 3.4 at the tail, to say the least, i even have a "mac" tailswitch to throw into the brew...

 

[csshih]

wasn't there something about resistance due to the anodization at the tailcap?

 

[Metatron]

wasn't there something about resistance due to the anodization at the tailcap?

may well be, but no ano here

 

[Metatron]

direct off the battery i am getting 3amp, so there is a loss in the switch i would think?

 

[mudman cj]

Mag switches are known to have quite a bit of resistance. Fortunately, there are tutorials on CPF for reducing the resistance to much lower levels. Some searching should turn them up.

 

[Metatron]

Mag switches are known to have quite a bit of resistance. Fortunately, there are tutorials on CPF for reducing the resistance to much lower levels. Some searching should turn them up.

i have modded the mag switch in accordance with 'he who cant be mentioned' and its gone from 1.4 to 2.7 so its looking a lot better folks!!:thumbsup:

edit: replaced the switch with an AW switch, now getting 3.0amp at the tail, man this led is bright, ty for ur guidance fellas!

 

[tx101]

g'day mate, read ur thread, very nice indeed, now if i could get a link to that batt that gave u 3.4 i would be up and running! i have the same host as u by the way! i am determined to get 3.4 at the tail, to say the least, i even have a "mac" tailswitch to throw into the brew...

The D cell came with a modded Mag I brought from him here

http://www.candlepowerforums.com/vb/showthread.php?t=225284


More information about the cell can be found here

http://www.candlepowerforums.com/vb/showthread.php?t=168809