Can 12V 2500 mah NiMH batteries release around 150A?

[jonnyk]

Hi,
I’ve recently come across brushless motors and their use in rc cars. The motor can supposedly bring a power of over 1000 Watts using for example NiMH batteries. BUT on those packs I read like say 2500mah, 12V , 5 AMPERE. Can an NiMH battery really release around a 150A current? If so can all NiMH battery packs do that? Thanks.

 

[russ_watters]

1000 W sounds impossible to me - certainly it wouldn't be over a very long period of time, since the amount of heat that represents is huge for a small motor (they'd be as hot as a lightb bulb if they were 90% efficient). 5 A seems pretty reasonable to me as a max rating (not that they don't exceed it...). If you run a car for 5 minutes and kill the battery that's an average of 2500/60*5=208 mA.

 

[jonnyk]

@russ_watters

1000 W sounds impossible to me - certainly it wouldn't be over a very long period of time, since the amount of heat that represents is huge for a small motor(they'd be as hot as a lightb bulb if they were 90% efficient). 5 A seems pretty reasonable to me as a max rating (not that they don't exceed it...). If you run a car for 5 minutes and kill the battery that's an average of 2500/60*5=208 mA.

JK- Could you explain this? Thanks.
from http://www.hobbypartz.com/ezbrescfor18.html

1 Specification
1.1 Output: Continuous current 150A, burst current 1080A.
1.2 Input: 6-18 cells NiMH/NiCd or 2-6 cells LiPo.
1.3 BEC Output: 5.75V/3A (Switch mode built-in BEC).
1.4 Resistance: 0.0002 Ohm.
1.5 Motor Supported: Sensorless and sensored brushless motors
1.6 Suitable Brushless Motor: 3.5T and > 3.5T
1.7 Suitable Car: 1/5, 1/8 on-road or off-road cars / trucks for competitive race.
1.8 Size: 68mm(L) * 55mm(W) * 45mm(H).
1.9 Weight: 150g(Without wires)

 

[f95toli]

It is probably a typo (it is definitely an error of some sort), the figures make sense if they mean mA; not A.

You would need AWG3 or thereabout to safely carry 150A; which means a conductor diameter of 5mm; hardly something you would use in a rc car,
And you would probably need a copper BAR in order to safely handle even a burst of 1080A.

 

[TurtleMeister]

I think NiMH/NiCd batteries have an internal resistance of somewhere between 0.1 and 0.2 ohms (at best). This would limit their short circuit current to somewhere between 6 to 12 amps. The specifications you posted may be for the device itself and not what you would expect to get when powered by normal batteries (unless you had a lot of them in parallel).

 

[waht]

You need to combine multiple cell packs to achieve 150 amps. It's reasonable to draw 10 amps from a cell for few minutes. Some of the lithium ion packs can put out 15-20 amps each.

 

[russ_watters]

It is probably a type (it is definitely an error of some sort), the figures make sense if they mean mA; not A.

That would be my guess too.

 

[russ_watters]

You need to combine multiple cell packs to achieve 150 amps. It's reasonable to draw 10 amps from a cell for few minutes. Some of the lithium ion packs can put out 15-20 amps each.

These packs are generally in series, so you'd need to rewire them to get them in parallel to put out more amperage.

 

[jonnyk]

@all
No it is not a typo. I looked further into it. The device which somehow allows for this is an ESC(Electronic Speed Controller) with which all brushless motors operate. Here are a few other examples of such devices being sold:
http://cgi.ebay.com/EZRUN-150A-SD-SENSORED-Brushless-ESC-RC-1-5-1-8-Car-U_W0QQitemZ180358462639QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item29fe33bcaf&_trksid=p3286.c0.m14&_trkparms=66%3A2%7C65%3A1%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50
http://cgi.ebay.com/Ezrun-1-8-RC-Truggy-Car-150A-Brushless-Motor-ESC-FAN_W0QQitemZ200335496912QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item2ea4ed16d0&_trksid=p3286.c0.m14&_trkparms=66%3A2%7C65%3A1%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50
http://cgi.ebay.com/EZRUN-2350-KV-21T-Brushless-Motor-150A-Program-ESC_W0QQitemZ300316198776QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item45ec3d8778&_trksid=p3286.c0.m14&_trkparms=66%3A2%7C65%3A1%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50

 

[TurtleMeister]

I don't think it's a typo. 150A is also printed on the device itself. When choosing ESCs it is normal practice to choose one that has at least double the peak current rating of the motor. 150A does seem a bit of an extreme overkill though. It's just the rating of the device, not the associated motor and wiring.

 

[jonnyk]

@turtlemeister

I don't think it's a typo. 150A is also printed on the device itself. When choosing ESCs it is normal practice to choose one that has at least double the peak current rating of the motor. 150A does seem a bit of an extreme overkill though. It's just the rating of the device, not the associated motor and wiring.

JK- But i looked at both RC nitro and brushless vehicles. The engine of a nitro normally has abt 1.5 hp or abt 1 KW. It travels abt 70 kmh. NOW the brushless electrics are claimed to be FASTER AND ALSO MORE ACCELRATION IN THE SAME CLASS. Check youtube "nitro vs brushless". This means the brushless must develop a peak power > 1000W. And they normally carry arnd 3000mah packs of NiMH. Sometimes LiPo but tht is special.

 

[TurtleMeister]

This means the brushless must develop a peak power > 1000W. And they normally carry arnd 3000mah packs of NiMH.

The mah rating of a battery has little to do with it's maximum current capability. If you are getting peak power of more than 1000 watts from a nicad battery pack then it would have to be one huge pack of batteries (and they would not last very long). There is no way that electrics can have a better power per weight ratio than nitro.

 

[jonnyk]

@turtlemeister

The mah rating of a battery has little to do with it's maximum current capability. If you are getting peak power of more than 1000 watts from a nicad battery pack then it would have to be one huge pack of batteries (and they would not last very long). There is no way that electrics can have a better power per weight ratio than nitro.

Almost the same. The weight of the brushless electrics is a little less than same class nitro but then the accelration is considerably more. You can type in "nitro vs brushless" on youtube and see for yourself. ALSO the battery pack usually consists of 6-8 cells NiMH NOT NiCd usually anymore.

 

[TurtleMeister]

I'm not an RC enthusiast so I'm not familiar with all the variables that must come into play when comparing electrics to nitros. However, I do know a little bit about electronics. The OP asks "Can 12V 2500 NiMH batteries release around 150A?". The answer is NO. 2500 mah does not mean the battery pack can deliver 150 amps for one minute. However, it could possibly deliver 2.5 amps for one hour. Batteries have current limits based on their internal resistance. You could short the 2500 mah battery with a copper bar and it still would not deliver anywhere near 150 amps.

 

[jonnyk]

@turtlemeister

I'm not an RC enthusiast so I'm not familiar with all the variables that must come into play when comparing electrics to nitros. However, I do know a little bit about electronics. The OP asks "Can 12V 2500 NiMH batteries release around 150A?". The answer is NO. 2500 mah does not mean the battery pack can deliver 150 amps for one minute. However, it could possibly deliver 2.5 amps for one hour. Batteries have current limits based on their internal resistance. You could short the 2500 mah battery with a copper bar and it still would not deliver anywhere near 150 amps.

Could each cell perhaps release abt 15A and then if there are 10 cells in the battery pack itd equal 150A together?

 

[TurtleMeister]

Could each cell perhaps release abt 15A and then if there are 10 cells in the battery pack itd equal 150A together?

No, they would have to be in parallel. IF each cell could deliver 15A you would have to have 10 in parallel and 10 in series to get 12V. So, you would need 100 cells in all. And even then they would be delivering their maximum current, and so would not last very long.

 

[jonnyk]

@turtlemeister

No, they would have to be in parallel. IF each cell could deliver 15A you would have to have 10 in parallel and 10 in series to get 12V. So, you would need 100 cells in all. And even then they would be delivering their maximum current, and so would not last very long.

Yes so ten 12V cells in parallel shoud do it or not?

 

[TurtleMeister]

A single nicad cell is 1.2v, not 12. But if you have a 12v battery pack that can deliver 15 amps then yes, you could put 10 of them in parallel and get 150 amps (for a short time). But, in this case your mah rating would probably be much higher than 2500.

 

[jonnyk]

@ turtlemeister

A single nicad cell is 1.2v, not 12. But if you have a 12v battery pack that can deliver 15 amps then yes, you could put 10 of them in parallel and get 150 amps (for a short time).

They use nickel-metal hydride(NiMH) cells. Why shldnt it be possible to make one cell of 12V?

 

[TurtleMeister]

NiMH cells are also 1.2v. If you have a 12v NiMH battery then what you actually have is a battery pack of 10 NiMH cells in series.

 

[jonnyk]

@turtlemeister

NiMH cells are also 1.2v. If you have a 12v NiMH battery then what you actually have is a battery pack of 10 NiMH cells in series.

JK- Is there a min size for a cell to have 1.2V? If not why not just cramp together 10 micro size cells in series and then further cramp 1000 such micro size battery packs together in parallel to get hell lot of amperage?

 

[Phrak]

What you are reading are the specs for the ESC, not the batteries.

NiMH is capable of far less discharge current than Lithium poly. Nickel metal halide and NiCads are about equal (same chemistry) and don't come close to exploiting the low series resistance, and current capability of that ESC. I've spent way too much time comparing these two technologies.

For batteries, you need to look at the "C" rating. For instance, if the battery is rated at 1200mAH and has a quoted C6, then it should be capable of outputting 6*1200 = 7.2 Amperes continuously.

I went to the battery section of the same company that sells the ESC's and they don't design to quote C values. No way would I buy their batteries.

Google "C rating batteries", and someone else might explain it better than I.

 

[TurtleMeister]

Is there a min size for a cell to have 1.2V? If not why not just cramp together 10 micro size cells in series and then further cramp 1000 such micro size battery packs together in parallel to get hell lot of amperage?

Decreasing the physical size of a cell decreases the amount of energy it can store. Battery energy storage is proportional to it's weight (MJ/kg) and it's chemistry. You can read about the different energy densities of batteries at Wikipedia: http://en.wikipedia.org/wiki/List_of_battery_sizes
jonnyk, I think you should consider giving up on the idea of running your RC on a 150 amp battery pack. :)

 

[jonnyk]

@turtlemeister

Decreasing the physical size of a cell decreases the amount of energy it can store. Battery energy density is proportional to it's weight (MJ/kg) and it's chemistry. You can read about the different energy densities of batteries at Wikipedia: http://en.wikipedia.org/wiki/List_of_battery_sizes
jonnyk, I think you should consider giving up on the idea of running your RC on a 150 amp battery pack. :)

JK- So then what is the problem? Instead of having one 1.2V cell of say 1 cm^3 volume have ten 1.2V cells in series each 0.1 cm^3 in volume. The voltage would now be 12 V and the weight and thus combined energy density should be the same or not?

 

[TurtleMeister]

JK- So then what is the problem? Instead of having one 1.2V cell of say 1 cm^3 volume have ten 12V cells each 1/10 cm^3 in volume. The voltage would now be 12 V and the weight and thus combined energy density should be the same or not?

No No No. Connecting batteries in series does not increase their amps. Ten cells in series has the same current rating as one cell. You have to connect batteries in parallel to get increased current and connecting in parallel does not increase the voltage. So you would have to have 10 in parallel and 10 in series (100 cells).

 

[jonnyk]

@turtlemeister

No No No. Connecting batteries in series does not increase their amps. Ten cells in series has the same current rating as one cell. You have to connect batteries in parallel to get increased current and connecting in parallel does not increase the voltage.

Yes i just forgot to mention the 2nd step. Say you have 10 cm^3 of space. First connect ten 1.2 V cells in series each 0.1 cm^3 to get a 1 cm^3 12V battery. NOW connect those ten 1 cm^3 batteries in parallel to get a 10 cm^3 battery pack with 12V and very high amperage. Why could one not do this on the micro level to get a huge ampere output with a relatively small battery pack?

 

[Phrak]

Decreasing the physical size of a cell decreases the amount of energy it can store. Battery energy storage is proportional to it's weight (MJ/kg) and it's chemistry.

Well, that's what I thought too. Try comparing Nickel metal halide AA's and C size, same same manufacturer, latest release. The double AA's have far more bang for per pound; about 1.4 times the energy density per unit mass.

Here's an example from Powerstream (and, yes, I do realize they are a distributor, not a manufacturer, so take it for what it is).
http://www.powerstream.com/BatteryFAQ.html"

AA NiMH, 1.2V, 2.0 AH, 28 grams, $3.73 @ 100
C NiMH, 1.2V, 4.0 AH, 80 grams, $6.97 @ 100

 

[TurtleMeister]

Yes i just forgot to mention the 2nd step. Say you have 10 cm^3 of space. First connect ten 1.2 V cells in series each 0.1 cm^3 to get a 1 cm^3 12V battery. NOW connect those ten 1 cm^3 batteries in parallel to get a 10 cm^3 battery pack with 12V and very high amperage. Why could one not do this on the micro level to get a huge ampere output with a relatively small battery pack?

jonnyk, this is just common sense. If what you're saying were true then we would have AAA size batteries to start our cars. :) You cannot decrease the physcal size of a battery and expect it to continue storing the same amount of energy (without new technology).

Well, that's what I thought too. Try comparing Nickel metal halide AA's and C size, same same manufacturer, latest release. The double AA's have far more bang for per pound; about double the energy density per unit mass.

Yes, new technology can increase the energy density. Also, some manufacturers of C size batteries are actually using AA's inside the C size battery.

 

[jonnyk]

@turtlemeister
Let me put it this way. Is it not as easy for a 1 mah battery to discharge at 5A as it is for a 500 mah battery?

 

[jonnyk]

@turtlemeister

If what you're saying were true then we would have AAA size batteries to start our cars

Actually i know a guy who started his car with an RC plane battery pack:
http://www.youtube.com/watch?v=1w_K08fwZnA&feature=channel_page

 

[Phrak]

Yes, new technology can increase the energy density. Also, some manufacturers of C size batteries are actually using AA's inside the C size battery.

That's not the case, here. But I wasn't referring to new technology, but the current technology of each. It may be an issue with thermal resistance.

 

[TurtleMeister]

Let me put it this way. Is it not as easy for a 1 mah battery to discharge at 5A as it is for a 500 mah battery?

Of what value is an RC that only runs for 15 seconds?

 

[jonnyk]

@turtlemeister

Of what value is an RC that only runs for 15 seconds?

JK- This was just an example. RC vehicles usually have 3000 mah packs as i mentioned earlier. And they only use peak power for a sec or so to accelerate rapidly every now and then.

 

[TurtleMeister]

This was just an example. RC vehicles usually have 3000 mah packs as i mentioned earlier. And they only use peak power for a sec or so to accelerate rapidly every now and then.

Ok then, can you imagine the physical size of a 3000 mah battery that can deliver 150 amps?

 

[TurtleMeister]

Actually, just because of the way batteries are made you would have to have much more than 3000mah battery to get 150 amps. And remember you would have 10 cells in series at .2 ohms per cell, a total of 2 ohms of internal battery resistance.

 

[jonnyk]

@turtlemeister
Example of an rc car with 5000 mah lipo battery pack with 25C discharge rate(25X5=125A):
http://www.youtube.com/watch?v=Vn1zNAvZp-8&feature=related

 

[cf8]

I'm surprised no one has pointed this out yet:

Actually i know a guy who started his car with an RC plane battery pack:
http://www.youtube.com/watch?v=1w_K08fwZnA&feature=channel_page

This is a perfect example of why you can't trust everything you see on the Internet. For curiosity's sake, what do you mean when you say that you "know" him? Have you actually met him? Did you do this yourself? The current required to cold-start a car is insane; that's why they use cables as big around as your thumb, and not 24 AWG wire like the guy in the video did.

 

[TurtleMeister]

Example of an rc car with 5000 mah lipo battery pack with 25C discharge rate(25X5=125A):http://www.youtube.com/watch?v=Vn1zNAvZp-8&feature=related

So we're talking about Li Poly batteries now? I checked and there is a battery of this type rated as specified. The 7.4 volt version weighs 247 grams and costs $125. And according to my calculations it would have to have an internal resistance of much less than 0.1 ohms. I did not know there were batteries on the market with such low internal resistance. And I'm still skeptical because I don't believe everything I read. :) But my answer to your original question is still NO.

 

[jonnyk]

@turtlemeister
Take a look at the Power on this table:
http://en.wikipedia.org/wiki/Rechargeable_battery#Table_of_rechargeable_battery_technologies

As you can see an NiMH battery has btw 250-1000 W/kg output AT 1.2 V which is abt 1.5 times less than the Lipo at the same voltage and weight but much more than the earlier NiCD. Hence at 12V an NiMH will have a 2500-12000 W/kg output OR a 250-1000 W/100g which is a feasible pack for rc cars.

 

[TurtleMeister]

Stacking cells in series does not increase the W/kg. If you double the voltage (power) by adding another cell you've also doubled the mass, so W/kg stays the same.

 

[vk6kro]

I weighed a single AA NiMH cell. It weighed 30 grams.
So, you would get about 3 of them in 100 grams.

They would give you 3.6 volts with an internal resistance of 0.3 ohms (if the previous figures for internal resistance are correct) so they would have a short circuit current of 12 amps. (3.6 /0.3 ). But short circuit means you don't get any voltage out.
Maximum power out of 10.8 watts would be available with a load of 0.3 ohms.
But at that power, the voltage would only be 1.8 volts. So the current would be 6 amps.

Just for fun, if you did somehow pass 150 amps through one of these AA cells, the power would be 150*150*0.1 or 2250 watts. I've never seen one of these explode but, if it was well sealed, it should be spectacular.

 

[Phrak]

This is a perfect example of why you can't trust everything you see on the Internet.

No you can't. But that video is plausible. Try this one.

http://www.youtube.com/watch?v=a2JkMCzjTVE"

Lithium Poly's are in a class by themselves.

 

[cf8]

No you can't. But that video is plausible. Try this one.

http://www.youtube.com/watch?v=a2JkMCzjTVE"

Lithium Poly's are in a class by themselves.

I re-watched the video, and I see your point. However, if I understood correctly, jonnyk was under the impression that the LiIon pack alone could cold-start the car - in the video, though, it was mentioned that the car battery did have some life left.

Also, I liked the video you just posted, that's amazing, however I did hear:

...powered by nine hundred ninety lithium battery cells...

Either way, I want a car made by them!

 

[Phrak]

I re-watched the video, and I see your point. However, if I understood correctly, jonnyk was under the impression that the LiIon pack alone could cold-start the car - in the video, though, it was mentioned that the car battery did have some life left.

Also, I liked the video you just posted, that's amazing, however I did hear:

Either way, I want a car made by them!

Well done. I didn't catch the part about the car battery still having life in it. lithium batteries have their drawbacks in terms of safety. Gasoline still stores energy better. Charging batteries burns coal. If mischarged they can burn real nice, and start a fire. But for peak power output in an electric vehicle, there's no comparison between NiMH and LithumPoly. I think the cost per Joule is about twice that of NiMH.

The series resistance of lithum polymere batteries seems to continue to decline. I'd have to check my notes to see what I was using 2 years ago to be sure (deit: I used 25 mOhms per cell). It may be to the point that the motor resistance is the predominant limit on output torque.

 

[TurtleMeister]

I wonder if anyone has ever considered using an ultracapacitor to enhance the performance of their RC? They have extremely low internal resistance and an amazing specific power of around 15000 W/Kg. Seems to me if you connected one of these across the input of the ESC it would help make up for some of the shortcomings of the battery.

 

[hean8209]

NIMH as used in RC cars have a discharge rate of 5-10C (C = times capacity).
So, with 3000mah nimh cells of good quality (10C) you would get 30 amps.
To get 1000 watts of power output, you would need a voltage of 36 volts,
which means 30 cells.. that would weight 2.5-3.0 kilograms approx, more than most 1:8 cars weigh.
Which translates to.. not very fast.

Good LIPO batterys have a 35C rating, and are available at 8000mah,
weighing only 0.3 kg if even that.
You could pull 3080 watts of power out of that battery alone,
with only 3 cells at 11.1 volt.
It would probably cost 200 USD for only one battery though.

Besides, with NIMH brushless is not on par with nitro in any way.. that's just hype.
you need LIPO to go fast, and you need expensive lipos to go really fast.
To expect anything else is to fall for the exaggerated hype.. an electric motor is only as good as its power supply, nothing more, nothing less.

Another thing on "power output".. a nitro engine is NOT 80-90% efficient,
so a lot of power dissipates as heat.. not drive.. and you can't expect a nitro engine to do
70 000 rpm (possible with brushless, but not safe, and the motor won't last long.)
Electric motors put out more efficient torque, and have a wider power band.. that is why
they accelerate better than a narrow band nitro engine (A lot of power at the last 2-3k of rpm)
All this translates to: higher final gear ratio possible for the same speed,
which means faster acceleration.
To equal 1000 watts on a nitro, at 30k rpm,
you would need twice the gearing, and twice the rpm, at 500 watts.
No big deal for an electric motor.
This, of course is if they weigh exactly the same, which they dont.

So 400 watts electric rc is more powerful than 1000 watts combustion rc,
hands down.
1 kw would equal more than 2.2 bhp, found in common .28 nitro´s in 1:8 cars.

Since the electric LIPO machines are lighter, you can gear them lower to get more speed,
and still accellerate like crazy.
That is why they are faster.. the factor of all things combined, not anyone part in itself.

Less weight + good powerplant + correct gearing = one fast mean car.

At the higher end (read: VERY EXPENSIVE 3 cell LIPO), sure brushless is faster, but costs quite a bit.
At the low end (read: VERY CHEAP 3000mah NIMH), brushless can't even compare, and nitro is the winner in performance no matter how many cells you put in (NIMH is heavy and low power).

I have tried BL and NIMH, and its really fun to drive with insane torque.. just don't buy a
too "hot" motor, or you will explode your poor nimh batteries.. 10 turn or higher works well with NIMH, anything lower REQUIRES LIPO.. don't even consider NIMH for those motors.

To sum up: The power in an electric RC car lies within the battery,
not so much in the motor. A poor motor with a good battery will perform much better than a good motor with a poor battery.

 

[uart]

Just for amusement here's another data point. The NiMH batteries in a Toyota prius are only 6.5AH yet they deliver peak current at around 100 Amps during acceleration. This corresponding to about 15C, though normally (for battery longevity) they deliver/receive considerably less than that amount.

 

[famousken]

Actually I have jump-started a car with RC car batteries. They were two 6 cell packs made of sub-cs, 1700mah, so 14.4V total. It worked, but one of the packs was no good after that. I think it is incredible how much current these batteries can supply, and they CAN supply upwards of 50A in short bursts, I have had shorts on the leads coming out of the batteries (AWG12) and it destroyed the silicon insulation on them, so there was way more than 20A flowing.

 

[The Electrician]

A brand new, just charged, Energizer 2300 mAH NiMH AA cell measures .027 ohms internal resistance (measured with a Wayne-Kerr LCR meter, .001 ohms resolution). Shorted into a 100 amp shunt, I get 35 amps. After 10 seconds of this, it gets hot; no surprise there.

 

[Altrepair]

I am surprised no one mention this so I will. A DC motor controller is like a buck converter in that varying the speed by voltage is done with variable square waves and the motor is like the inductor that stores the energy. One-hundred fifty amps could be supplied to load from a buck converter while pulling less current from the power source such as a battery. But this is an indirect way and the voltage will have to be less on the output. I doubt a direct connection to this battery would allow 150 amps to be pulled from it. If it could then the battery will most likely never function again. Lithium Ion batteries seem to be a totally different animal all together.