Max draw from D cells?

[poormanq45]

I'm looking at making a ROP for my first mod.

I've got plenty of D maglites of all sizes.

I have a 6D that is a little bulky, but not too bad. I'd like to use it to make a ROP mag.

From most of the threads I've read people use the 3d and 2d with 3AA>1D type adaptors.

What i'm wondering is can I just use my 6d with NiHM batteries to achieve the required 7.2v. The draw of the low bulb is what, 2 amps? The high being ~5 amps. Can 6 Ds handle this?

Thank you

 

[mdhammack]

Not a problem whatsoever!! You will get great runtimes with that setup too.

 

[RaVeN38571]

Just make sure you get some good nimh batteries. For example energizer D batteries only have 2500mah, while Titanium D have 12000mah. Thats a big difference in runtime. They do cost a little more, but are well worth it. Here is a link to the Titaniums.

http://www.batteryjunction.com/tpeh-td12000.html

 

[poormanq45]

Thank you for the info.

I was looking at the different D NiHMs. Are the energizers just AA cells in a D platform?

Next question. I have a 3D with the MagnumStar bulb. I don't want to do a Mag85. Basically I'm cheap and don't want to order the 9AA>3D. Will the 6 1/2D NiHM 3500mAh be able to support a ROP? If this would work it would have longer runtime then a 2D with 6AAs, correct? I'm looking at it as 2700mAh AAs vs 3500mAh 1/2Ds. Is that correct, and will that work?

Also, if 1/2Ds work, what charger would you recommend? Is there one that fits these cells? Should I make leads to fit a regular NiHM charger? Resist down a 3.6v charger?

Thank you for the help

 

[Kestrel]

Does AccuPower make a low-self-discharge NiMH 'D'? If so, those would be perfect.

 

[gswitter]

Does AccuPower make a low-self-discharge NiMH 'D'?

They do indeed.

 

[3000k]

Would this work with alkaline batteries? If not would it work with D size lithium batteries (if there is such a thing?)

 

[Kestrel]

Would this work with alkaline batteries?

I've done a fair number of alkaline builds (AAA's, AA's, C's, & D's) over the past year or so, the 3854-L (at ~2 amps) would be sort of OK. The total watt-hours that alkaline D's can deliver at that high of a drain rate falls off dramatically, they don't perform at all well past ~1.5 amps or so. The 3854-H (at ~4.5 amps), no.

I did some calculations not too long ago (based on data posted by Silverfox) that showed that an Alkaline D loses something like ~3/4 of its watt-hours at ~1.75 amp drain rates or so, whereas even the lowly NiMH AA can deliver something like ~90% of its watt-hours at a much higher 4.5 amps IIRC (i.e. NiMH AA's can actually have more usable capacity than Alkaline D's at high drain rates!).

I figure one reason that the 2D ROP is so popular is that 6x AA NiMH in a 2D holder just crushes a similar (but much larger) build that uses 6 D alkalines.

 

[Mjolnir]

With 6 nimh cells you could make a mag 5671, although you may need to let the cells rest for a little bit to avoid clowing the bulb. You would only need a bi pin holder to convert it to 5671 (and the same metal reflector and glass or borofloat lens that you would use for an ROP of course). A 5671 should be a bit brighter than an ROP high.

For a charger you might want to consider the Turnigy Accucel:
http://www.hobbycity.com/hobbycity/store/uh_viewitem.asp?idproduct=7028
For 45 dollars ($35 for the charger and $10 for a 12 volt 50 watt power supply), you can charge up to 15 Nimh or NiCad cells, or up to 6 lithium ion cells. Charging 6 1/2 d cells should be fairly simple; you may need to use a fw magnets to hold the charging leads on.

 

[poormanq45]

Thank you for the responses. I didn't even think of using little disc magnets. That will work perfectly!

I'm having a little difficultly finding threads on modifying the switch. How important would it be in this build? I want to maximize the output of this build. I understand that resistance is a killer. First thing up is to run a 14awg wire across the tail spring, correct?

 

[poormanq45]

What do you guys think of using these larger Li-Ion cells?

http://kaidomain.com/ProductDetails.aspx?ProductId=2751

They are rated at 5000mAhs. Compared to 18650s you're getting ~100% more runtime. Has anyone tried these?

Two for a ROP, three for a Mag85, correct?

 

[fivemega]

What do you guys think of using these larger Li-Ion cells?

http://kaidomain.com/ProductDetails.aspx?ProductId=2751

They are rated at 5000mAhs. Compared to 18650s you're getting ~100% more runtime. Has anyone tried these?

Two for a ROP, three for a Mag85, correct?

They don't have current capability of 4.4A ROP Hi unless used with soft start.

 

[Mjolnir]

I would suggest these:
http://www.batteryspace.com/limnnirechargeable26650cell37v4000mah10arated148wh.aspx
They are cheaper than the KD cells, and are rated up to a 10A constant discharge. They are unprotected though, so they can be over discharged. However, they are of a safer chemistry than the "normal" LiCo lithium ion cells (like the KD ones and most 18650s), so they will not explode or catch fire even if you overcharge them or charge them after they are over discharged.
If you make an ROP with them then you should use the 3853H bulb. The 3854H bulb works (at least up to about 4.15 volts, but I haven't gone higher than that) if you don't do any fixes to reduce resistance, but if you do do the fixes you might blow the bulb with these cells. Apparently 2 IMR C cells will blow a 3854H, but these are slightly different from IMR cells and might have a slightly lower voltage under load (since these are rated for 10A and the IMR AW IMR C cells are rated for 20A).
3 will fit in a 3D maglite, but they also might blow an 1185 bulb. An alternative is Fivemega's FM1909 bulb with 3 of these cells. It should run fine with 3, and output 2000+ Lumens (a lot more than an ROP or MAG85) for a good half hour. You can get them with purchase of his bi-pin holder (which you would need anyway).

 

[poormanq45]

Isn't the High bulb in the ROP kit rated at 9v which is actually 7.2v, correct?

If so, two of those cells you recommended would work, right?

Thank you very much for the information