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.