9N 90 minute NiMH battery

[hmmwv]

Fellow 9N users -

Just a note to let you know that thanks to the RC hobby industry, sanyo and panasonic have now produced a 3000 mAh sub-c NiMH cell - the exact size used in the 9N battery pack from surefire - which uses 1450 mAh NiCD sub-C's

Unfortunately, due to the cost of the cells ($7.95 ea x 3 per pack = $24 in batteries alone) and the complexity of the charging circuit (the existing 9N chargers from surefire won't deliver the 3A needed for these cells to achieve their full capacity) - it's unlikely that surefire will ever offer this as an option. They did at one time replace the 1200 mAh NiCd with a more modern 1400 mAh cell - which "upped" the spec'ed runtime from 40 to 45 minutes - but they have positioned the product to stay with NiCD chemistry due to the charger designs. NiMH cells need to be used with "fast" chargers running a 1C rate (in this case - 3A !!)

I am presently prototyping a battery for the 9N constructed of these 3000 mAh cells and a charger (4.0 V @ 3.0 A, with intelligent charge control, top-off, and trickle). If you have an electronics background - it's not a bad DIY project - but anticipate $65 in parts to fully retrofit a 9N with the upgrade, somewhat less if you happen to have a good junk-box full of charger parts.

You have to consider if these costs outweigh the double runtime advantage (for me - it's an easy "yes" since I frequently go through 2 packs in a row).

 

[Brock]

Ok I am confused. I have used NiMH batteries for a LONG time now and it was always my understanding that they needed to be charged at a lower rate than NiCd? I thought you could run NiCd at C1 and NiMH were suppose to be C4?

Confused?

Even so couldn't you use the existing charger and it would just take longer, or is the "smart" part of it fooled in to thinking the batteries are charged before they really are?

I haven't tried it yet but could you leave the 3 cub-c's apart and use s NiMH charger for them?

Brock

 

[dano]

Back in my R/C racing days (I won a bunch of trophies with my R/C 10..WooHOO!) the cell to have was Sanyo's SCE, sub-c battery.

The latest Sub-c's are 2000MAH in capacity, the NiMH's are upto 3000MAH in capacity. I've toyed with the idea of making a NiMH pack for my Stinger, but haven't had the time. I don't see why it wouldn't work, and in the near future, NiCads are going to be phased out due to environmental concerns.

--dan

 

[hmmwv]

re: charge rates -

Every chemistry has it's own preferred charge pattern -- NiCD and NiMH are very close, but while NiMH chargers are "backwards compatible" with NiCD, the cheap NiCD chargers can actually damage NIMH cells - The surefire design is simply a resistor/diode to produce a constant current source forever. It's 50 cents worth of parts, never meant to charge a $24 battery. Most NiCDs can tolerate C/10 forever -but NiMH needs a "shutoff" at the end of the charge, which NiCD chargers don't always produce.

(unless you splurged for the rapid charge surefire - which may be NiMH compatible, provided it shuts off when charged, instead of a neverending trickle, and even then it's not likely to fully charge the NiMH)


To achieve the maximum charge capacity in a NIMH cell - charge ASICS have been developed by several companies (unitrode, benchmarq, etc) to do a "pulse charge" starting at 1C steady state, then switching to either a "top-off" or a "maintenance" charge - in all 3 states, the current amplitude is usually matched to the cell's capacity, but the pulse duration is shortened. If the battery is left in the charger, a periodic 1C pulse is sent to keep the battery "full" as it self-discharges.

These ASICS monitor the whole charge process very closely - watching cell temperature, voltage, current, and time spent charging. As a result, they can maximize the charge in NiMH cells, and also handle NiCDs just fine -- mainly because the NiCD is so tolerant. They deliberately overcharge the NiMH cell because it requires more current x time to reach 100% capacity.

The 1C rate is from the spec sheet for the 3000 mAh cells - most NiCDs can also take 1C, most notably the "rapid charge" rated cells, which can take even more - but a few models are not rated for rapid charge, and should be limited to C/10 - these are becomming more scarce now, but are still listed in the sanyo catalog. I've seen a few rapid charge NiCDs are rated for an extreme 4C (15 min) rate under certain specific conditions, while NiMH cells generally don't like more than 1C (although one IC mfgr makes a 2C NiMH program for special applications)

There are some problems implementing the NiMH chemistry on the surefire 9N - first is the pack construction with all the safety devices in place. The temperature monitor also needs to be calibrated to measure through the body of the flashlight (since the cells inside are quite a bit hotter than the barrel) - when I'm done with this it will be a specific solution for this flashlight!

 

[BKO]

Glad to see other people have an RC background!!..I once was 10th scale off-road truck and buggy champ in Alaska..Qualified for ROAR & IFMAR Championships..Anyway back to the subject...Ive been using a 3000mah NiMh(Panasonic)battery pack in a 9N for a while..Works great!!..They can be purchased in most hobby shops.prices vary,depending on "matching specs"..i.e.voltage,internal resistance,discharge rate etc...You can purchase a good pack(matched)of six cells for around 60.00-70.00usd..Makes two 9N packs...Get some flexible solder tabs and some sub-c shrink wrap while your there.
Disassemble a 9v battery or purchase a "button"(for positive end)..Solder(or spot-weld,if equipment available).Shrink-wrap it and Viola!! Two NiMh 9N packs..Now the problem..Charging..I have used the 9N charger(battery removed model)and it works ok..takes about 12 hours(slow charge model).Ive also used a "Super IQ" charger(retained from my RC days)..When connected to a lap-top or PC you can specify cell number,charge rate,type i.e. peak,flex,thermal etc..you can also "condition" or train them-discharge at same rate as application and record performance..Be aware, most chargers available to RCers are set for 4-7 cells(9N--3 cell).
I just purchased a new digi-cam(wifes X-mas gift)...will post pics,after figuring it out.
Charge rates:Im still experimenting.Ive peaked charged(voltage peak)at 3amps-no problem,I know this isn't good for batt. life,but,it worked in a pinch.Considering the cost & the fact that I have several 9N packs Ive since been using a thermal cut-off cycle..So far so good!
Rgds,Bill

 

[Dennis]

I have built two battery packs with NiCD Sanyo RC cells, 2000Mah and 2400Mah. The 2400 lasts almost 90min in my 9NT. I use my "intelligent" Tekin RC charger to charge them as well as my Streamlight SL20x, RC car, 2way radio, and airsoft batteries.

My local RC shop had the cells with tabs as well as the correct shrink wrap. I soldered on a 9v battery tab on for a + connection. They have been working great for a year now.

The Sanyo NiCD's made for the RC market are really tough. They can be quick charged, discharged, and charged right away without hurting the battery. (Well, too much at least...) I haven't been too impressed with the NiMH batteries for high Amp drain applications. They definitely have less "punch" and acceleration in my RC car. I also don't believe they are as tough as the Sanyo cells.

Go for the 2400mAh cells, they work great.

 

[hmmwv]

Glad to see I'm not the only one making better batteries for the 9N - going with the 3000 sanyos (if sanyo delivers - which is questionable today) -- should make for a long lasting light when done - I'll post test data after it's all finished.