yahman1254

My Feedback: (1)

i was wondering if anyone has tried to use 9v cells to make a nimh battery pack. their capacity isnt usually that much but you could wire it up so the capacity adds up? i wonder if it would work.

DaveG55

Nimh cells are 1.2v each, not 9v. If you have a 9v nimh pack then it's made up of 1.2v cells and will either be 8.4v or 9.6v. You can use standard AA batterys to make a pack but they are really only good for rx packs in nitro or for transmitters. AA's are an odd size and do not really fit well in most rc applications. Most rx hump style packs use a "2/3 AA" size cell and most stick packs use "sub C" cells. Those cells seem to be the best compromise between size, weight and capacity.
But, yeah, if you want to make macks out of over the counter nimh's they will work in certain applications

yahman1254

My Feedback: (1)

sorry, i think you miss understood me. i was refering to the small 9v cell that goes in your smoke detector. these can be found as rechargeables and i was thinking that a whole bunch of these in parallel could have interesting results.

hands without shadows

9v batteries are made up of 6 AAAA cells that can only withstand a small drain. I think if you wire up enough of them to power an RC it would weigh more than a standard pack, have less capacity, and be a PITA to charge.

DaveG55

No, I understood you very well. Those batterys are 8.4v. See the link below
http://www.thomas-distributing.com/m...ery-300mAh.php
You'll also notice that they are only 300mah. Yes you could wire a bunch, and I mean a BUNCH, of them in parallel to increase the overall capacity to something usable. But to get 3000mah you'll be looking at almost $120.

But hey, it will "work" if that's what you want to do. Personally, I'd just spring for some high capacity, matched sub c's and be done with it.

DaveG55

It would have to be 7 of them to be 8.4v and I think that they would be bigger than a standard "9v" battery. But I don't think that I've ever seen a quad A battery so I don't know for sure.

SAVAGEJIM

I didnt even know that 9V batts came as rechargeables. H3ll, I didnt even know c and d cells came as recgargables either, but they are there.

9V is such an odd voltage for RC use, get 2 of them in series, you get 18V, 3 and you get 27V, etc.

I guess that is why our 1.2V NiMh rechargeables are more popular, they can be added or taken away in small increments to get the right voltage. For example, in my Futaba Megatech AA batt tray, 8 AA cells give right at 9.6V, but turning on my Futaba right now, the AAs, being freshly charged, are now pushing 10.2V, a little more than the rated 1.2V per cell.

DaveG55

Jim, all nimh batterys are made up of 1.2v cells. Just like all lead acid batterys are 1.5v/cell and lipo batterys are 3.7v/cell. It's just battery chemestry. The "9v" batterys shown are really 7 little 1.2v cells packed into a 9v battery configuration for a total of 8.4v. The voltage stated for batterys is the nominal voltage. The actual voltage will be higher when they are charged and lower when discharged. Look at your car battery. It's made up of 8, 1.5v cells for a nominal voltage of 12v. But when it's fully charged it will have a voltage of (I forget exactly) around 14V and a discharged voltage of around 10v. Nimhs and lipos are no different, they have a nominal voltage and a fully charged voltage and a discharged voltage. Of course over charging or over discharging will cause damage so knowing the exact upper and lower voltages is obviously important

SAVAGEJIM

Makes sense.

What really bothers me to the point of a pet peeve is that Nimh is capped off at 1,2V where throw-away batts are 1.5V per cell! [:@]

I cant wait for rechargable AAs will exceed 1.5V per cell.

yahman1254

My Feedback: (1)

dont get me wrong, i was just wondering if anyone thought of doing this just to get a super high capacity battery cuz i found ones that are 720 each. i will stick to my sc's personally

DaveG55

You'll have to wait a long, long time I imagine. As far as I am aware, there is no recharagable battery technology that gives 1.5v. It's not like the chemestry of nimh batterys is going to change to bump up their potential (voltage) - it's not the same thing as their capacity which seems to move up monthly. Lipos do give over 1.5v/cell but they are more than double at 3.7v/cell. Lipos do come in a size similar to the sub c cells, check into the A123 cells.
I think the next revolution you'll see in battery technology won't even be a chemical battery. It will be a form of extremely high storage capacitor. That technology has a lot of potential, high discharge rates, fast (less than 10 minute) charging, non explosive, no heat build-up (either charge or discharge), non hazardous to the environment, etc, etc, etc. If this stuff works it has the potential to revolutionize our society - seriously.
here's an article that talks about it some
http://www.treehugger.com/files/2006...capacito_1.php

yahman1254

My Feedback: (1)

yea i read something about that. super capacity capacitors is like hard drives so fast you dont need ram...

DaveG55

You're going to be hard pressed to beat the capacity of lipo batterys. I've seen 10,000mah batterys for rc's and have heard of lipos with 25,000mah capacity with an 85C discharge rate.
Yeah, you can make the 9volters work but there are far better alternatives.
That's my thought anyway.

yahman1254

My Feedback: (1)

yea, obviously its not the most practical...

redfisher1974

Good read.....

Ttam Says Blarg

Just wondering. How big are these 25,000 mah batteries? Could they even fit in a 1/10 scale?

yahman1254

My Feedback: (1)

im doubting it

DaveG55

Sorry, not a clue what size they are. I saw them in an article somewhere on the net. I don't even know what they were intended for. I was impressed by their capacity though, I mean really, 25 amps capacity with an 85 amp draw. That's enough to start my lawnmower!!!