experimental_pilot

I have a couple of these already and just want to know if I can use these instead of getting a "hump pack"?
Also, for the Tx. do they sell any 8 cell packs that fit in the transmitter, instead of using seperate AA's?

DaveG55

No, that is too much voltage for the reciever. It needs 6v, more will eventually (if not right away) cause it harm.

It depends on what radio you have. Lots of people just buy rechargable AA's and use them. The voltage is a bit low (9.6v) but it works pretty well. Others have made various mods to accept 9 or 10 cells in the tx and still others use 2/3AA and fit 10 in the space of 8 standard AA's

experimental_pilot

That sucks.
4 AA's don't add up to 9.6V? [sm=confused.gif]

I have rechargeable AA's as well, but packs are just more convenient. So, how much run-time could I expect from 4 AA's?

Nick2618

reg aa bats are 1.5v and rechargalbes are 1.2v. Also 650 mah is really low for a hump pack. They average around 1100-1600mah.

experimental_pilot

I just checked my Tx. battery for a Futaba Air system. This should work for the Tx.

9.6V 600mah


--
So, I guess this one would be no good for the Rx?

Dawman

My Feedback: (33)

9.6 is pretty low as many radios won`t do well at that voltage and have an alarm when the battery gets to 9.9 and below . I use 2650mah rechargeable AA`s for my tx and use five of the same type batteries to make my own rx packs . Both are the proper voltage and last a long time before needing recharged . Also 600mah isn`t going to get you far and you really don`t want to use nicad for rx and tx packs either.

DaveG55

Dawman,
8 rechargeable AA's are 9.6v --- 1.2v x 8 = 9.6, You would need 10 rechargeable AA's to make it to the "correct" voltage (12v) for the TX.
And unless Duracell has come up with some new technology, those batteries in you picture are 1.2v each.

Experemental,
Those batteries will power what you want them to - just not for very long

Dawman

My Feedback: (33)

That`s what I thought , but when I charge mine for my radio they read as high as 11.1 but usually read 10.8 and I can run three race days until they get down to 9.9 when my alarm lets me know they are getting low . So not sure how they are producing more than 9.6 ? When I get home from racing tonight I`ll charge them and get out a meter and see what`s going on . And it`s not like I just started using these either , I have been using rechargeable AA`s for years and always been like this .

DaveG55

What your looking at is the difference in voltages between nominal (what the battery's are rated at) and the fully charged voltage of a battery. There are terms that I cannot remember offhand for the fully charged voltage and the discharged voltage of batteries.
But, basically, the voltage of a battery will vary some depending on it's state of charge. All batteries have a nominal voltage that depends on the material the are made out of. Lead acid batteries have 2v/cell, alkaline have 1.5v/cell, nickel batteries have 1.2v/cell, lipos are 3.7v/cell but each of those batteries, when fully charged, will exceed that voltage. For example the lead acid battery in a 1:1 car has a fully charged voltage of 14.4v. And that is what you are seeing when you measure the fully charged nimh Duracell batteries. Conversely, each type of battery has a lower limit of voltage past which the battery will suffer significant damage. In lipos that voltage is 3v/cell. The mah rating of a battery is the amount of current the battery can deliver and basically defines the amount of time a battery will provide power between full charge and full discharge.
I know that explanation is lacking a lot but I hope it gives you the idea.

mazdab2600

i use these now.
i guess it depends on the person.
i used alki's and thought they where great.
but after getting the 3rd truck running and going through 8 aa's per tx.the garbage filled quickly.
for me bashing these have saved me lot of cash and worked great. last me more than a day on a charge.
as you noticed the voltage is not 9.6 but up around the 11.v mark. mine are like this as well.

dacaur

Sorry, but this is completly wrong... every (non-2.4) radio I know if is powerd by 8 AA batteries, all of the higher end ones come with rechargable packs with 8 cells (9.6v). When a battery says 1.2v what you are seeing is the "nominal voltage" which is what the voltage will read when the battery is resting and nearly depleted. a fully charged 9.6 volt pack will read closer to 11.6v which is why you will never see a "full" battery meter on your radio unless you are using brand new alkalines (1.5v x 8 = 12v) Rechargables are 1.45V fully charged, 1.45 x 8 = 11.6v. The fully charged voltage of 10 AA nimh cells is 14.5v.... too high for a radio....

Nominal voltage for nimh = 1.2v. fully charged = 1.45
Nominal voltage for lipo = 3.7v. fully charged = 4.2v

DaveG55

Actually, I'm not wrong. What I said was completely correct.

And if you would have read my next thread you would have seen that I explained about nominal voltages also. And finally, 10 AA rechargeable batteries is not too much for a tx any more than 5 rechargables in a hump pack is too much for an rx. When you are trying to determine the batteries needed for an application, any application, you always use the nominal voltage, not the fully charged voltage. You cannot count on the fully charged voltage because as soon as battery usage begins that voltage drops begin.
If your theory were correct, which it's not, then auto batteries would only be rated at 10v since 5 lead acid cells would have a fully charged voltage ov 12v. But we know they are not. They have 6, 2v (nominal rating) cells and a fully charged voltage of 14.4v, even though it's called a 12v system because, again, you determine battery requirements based on nominal voltage.

experimental_pilot

How much run time would I get with 4 AA's onboard?
The rechargeable's I have are NIMH 2300mah.

So, that Futaba Tx. pack is fine voltage wise, but the mah is too low?
I though if it works for the 4channel Air radio, it should be fine for a 2 channel Ground radio?

dacaur

OK, first off, where do you get that a fully charged car battery is 14.4v? 100% wrong. Lead acid cells have a fully charged voltage of about 2.1v/cell The charging system in a car puts out a max of 14.4v yes, but fully charged a car battery is around12.6-12.7v... go check the voltage of your car battery now (while the car is off) if you dont believe me, I bet its about 12.6-12.7 volts if the battery and charging system are in good shape. When a car battery reaches its nominal voltage of 12v, it is nearly completely discharged... its not a theory, its a fact.

Now, let me just make sure I understand what you are saying....
So what you are saying is that every radio MFG in the world that supply's 8 cell rechargeable packs for their radios is wrong? they should be supplying 10 cell packs? Your argument here makes the assumption that radios are designed for 12v nominal... this is certainly not true, its 9.6, or mfg's would be selling them with 10 cell rechargeable packs, not 8 cell. If they were designed around 12v, then every MFG in the world is selling their radios with batteries with to low of voltage... does that make sense to you? Hey i have an idea, do us a favor and hook up a 10 cell rechargeable pack to your radio and use it for a month and let us all know what happens, k? You claim this is a common mod, but i have NEVER heard of anyone doing it, got any examples?. and using a 2/3aa pack to fit 10 cells? well that would be really stupid, because you would have way less capacity, considering that 2/3AA packs normaly aren't more than 700mah, and lots of capacity is what you want in a radio pack. (2500 + mah) There is no reason in the world to use 10 rechargeable cells in a radio, since it was designed for 8... why do you suppose it is that the voltage scale on radios only goes up to 12 volts?

What it comes down to is this, for you to sit there and tell someone that 8 rechargeable batteries will not work for their TX, or will just work "OK" but is not ideal, is not only wrong, but just asinine.. 8 rechargeable will start out at about 11.6v and drop down to the 10.4-10.6 range and stay there until they are almost depleted and then the voltage will drop down sharply to the Tx's alarm voltage. What part of that sounds like 8 aa's is too low? An alkaline cell on the other hand actually starts at about 1.6 volts, but as soon as you start using it, the voltage starts dropping in a linear fashion, that is, the longer you use it, the lower the voltage gets. so its isnt long before the voltage of the alkalines meets the rechargeables...

DaveG55

We are obviously not going to agree on this so, I for one intend to stop hijacking this thread.
I know what is correct and do not post incorrect info. But, whatever, from this point out I'll let the readers make their own decisions.
You feel free to have the last word though, I'm done.

dacaur

run time wil depend on your driving style, I never tried using a 4aa rechargable pack so i cant help you there.

For the TX pack yes it will work fine. The lowe Mah just means that you will have less usage before its time to recharge it. Typical radio draw is 170-250mah, so a 600mah pack will give you, in theory, between 2.4 and 3.5 hours. In reality it will be less. First off your battery alarm will go off long before you have used the full 600mah. Second, you probably wont use all that time in one day, and a nicad pack will self discharge about 1% per day. and third, the 600mah packs that come with radios are pretty crappy, depending on how old it is it probably has less than 600mah capacity, and the crappy cells mean a higher self discharge than 1%. Basicaly my opinion is to use the pack for a max of 1.5 hours, then recharge it....

dacaur

not trying to get the last word here, but do you actualy believe that a fully charged car battery is 14.4v? If thats not wrong info I dont know what is...

Dawman

My Feedback: (33)

I have to agree as I know this from working or my trucks and cars .

DaveG55

OK, I said I was done and I apologize to experimental_pilot for further hijacking his thread.

This is a quote from BatteryUniversity.com, a site that has very good information on all kinds of batteries and is written by a very knowledge man, a man that has made his living with batteries and chargers for many years and is considered an expert in the field.

"Car batteries and valve-regulated-lead-acid batteries (VRLA) are typically charged to between 2.26 and 2.36V/cell. At 2.37V, most lead-acid batteries start to gas, causing loss of electrolyte and possible temperature increases. The exceptions are small sealed lead acid batteries (SLA), which can be charged to 2.50V/cell without adverse side effect."

For anyone w/o a calculator, 2.36v x 6 cells = 14.16v (my previous statement of 14.4v was off by .24v. Sorry I was working from memory)

Here's the link to the entire article if anyone would care to verify my information is correct and not just repeated hear-say.

http://www.batteryuniversity.com/partone-13.htm

experimental_pilot, again I appologize for taking your thread so far off track.
I am truly done with this thread and will not be posting here again.

Nick2618

For the record i use these batteries also in my traxxas radio with no problems... and would recommened them they work good and price was not that bad.

dacaur

Right, they are charged at up to 14.4v... but once the charge stops and you check the voltage, it will be about 12.6-12.7 honestly you can quote all the articles you want, but all someone has to do is walk outside with a voltmeter to find the truth...

nitro _ burner

I use Varta 15 minute rechargables, they work fine for me!

BTW you can get 3/2AA cells up to 1600 Mah, so who ever said they are about 600, is wrong!

Dawman

My Feedback: (33)

You can get them with more mah rating also .

dacaur

You are thinking of 2/3 A cells, not 2/3 AA.... you can definatly get 2/3 A batteries in higher mah ratings, but there is no way you could fit 10 of them in a spaced designed for 8 AA battereies...(they are too fat) 2/3A are differrent than 2/3AA. 2/3AA are smaller and have a lower capacity. best I have seen is 700mah....

nitro _ burner

Ohh, im thinking of the RX reciever batterys, or the 1/18 batterys...