3 of KD's li-ion's in parallel

[DocD]

hi,
Can this be done? i have a 3D M*g with a P7 is it possible to run 3 of KD's D-cells in parallel for use in DD or regulated?, i think this will increase the run time? but i might be wrong or will all the mAh join together damage or blow the P7.
I'm just trying to fit as much power into a 3D for a P7 to get max run time:candle:
cheers and thanks DocD

 

[LukeA]

In parallel 3 Li-ion Ds won't sag enough under the load to drive the P7 at a reasonable current. I think you might fry it.

 

[uluapoundr]

3 D NiMh should do just fine, that's what I'm running mine on at 2.8A direct drive. How were you going to run 3 Li-ion D cell in parallel in a 3D mag?

 

[lasercrazy]

I doubt you'd fry the led, but I'm not sure how you would wire the cells up. :thinking:

 

[2xTrinity]

If you're going to go parallel, might as well only use 2D. I don't think there's any way a P7 at full drive can come anywhere close to the using up the full 15Amp-hour runtime of 3Ds continuously without the host getting uncomfortably hot from all the waste heat, anyway. Do ou really need that much runtime? IMO, some sort of 'cutdown' host with only 1D would be more impressive, and would still offer about 90mins runtime (again, even that you won't be able to get all at once without say sumberging the entire light in water).

 

[DocD]

thanks for all the replys, they got me thinking is there a way to control the voltage smack on 3.6 volts even if the total battery voltage was higher say 4.1volts then pass this controled 3.6v to the same set up as
StefanFS P7 the 3.0amp driver had uses or am i missing the hole thing here? DocD

 

[StefanFS]

thanks for all the replys, they got me thinking is there a way to control the voltage smack on 3.6 volts even if the total battery voltage was higher say 4.1volts then pass this controled 3.6v to the same set up as
StefanFS P7 the 3.0amp driver had uses or am i missing the hole thing here? DocD

No, you're not missing it. The SSC P7 in a Mag and regulation with AMC7135 to 2.8A or 3A is ok with 4.2V from a LiION cell (or maybe 2 D LiION in parallell, which is a risky solution). With 3 x D NiMH in your 3D Mag you will get an initial voltage of ~4.2V, those big cells will keep voltage under load pretty good. But the voltage goes under 4V pretty quick in that kind of setup and stabilize around ~3.6V. The emitter gets hot when driven at 2.8A-3A, so the heat you get is from the emitter, not from the drivers. To get less heat and more runtime you need to use max 2.2-2.4A drive current, you will lose ~20% of the output compared to 3A.

With that said I have been running a both of my 1D SSC P7 Mags at 3A for over one hour at a time without overheating, but it's advisable to hold the light in your hand for longer periods to bleed off heat. In actual use it's no problem to get full runtimes off a D size LiION. But if left on a table on high, then it will overheat in time.

Another way is to use one D LiION and one dummy cell or 3 C NiMH in a 2D Mag. But with a voltage in of max 4.5 and a low vf SSC P7 the setups discussed are unbeatable for the price and performance you get.

Stefan

 

[2xTrinity]

No, you're not missing it. The SSC P7 in a Mag and regulation with AMC7135 to 2.8A or 3A is ok with 4.2V from a LiION cell (or maybe 2 D LiION in parallell, which is a risky solution). With 3 x D NiMH in your 3D Mag you will get an initial voltage of ~4.2V, those big cells will keep voltage under load pretty good. But the voltage goes under 4V pretty quick in that kind of setup and stabilize around ~3.6V. The emitter gets hot when driven at 2.8A-3A, so the heat you get is from the emitter, not from the drivers. To get less heat and more runtime you need to use max 2.2-2.4A drive current, you will lose ~20% of the output compared to 3A.

With that said I have been running a both of my 1D SSC P7 Mags at 3A for over one hour at a time without overheating, but it's advisable to hold the light in your hand for longer periods to bleed off heat. In actual use it's no problem to get full runtimes off a D size LiION. But if left on a table on high, then it will overheat in time.

I suspect the same is true of many of my hotwire lights -- my ROP for example I can run a lot longer without overheating if it's in my hand (bloodflow/circulation is in effect liquid cooling), and being waved around in open air outdoors, than tailstanding on a table -- where it will get hot VERY quickly.

IMO that's why I believe most stock new LED lights should attempt to implement a thermistor as part of the driver feedback loop, to dim the output if the temperatrue gets too high. This is probably an easier approach than engineering a heatsink that will be able to dissipate the heat for hours on end, especailly when most peopel probably only use the light for a few minute long bursts at a time anyway.