Nickel Metal Halide Vs Lead acid battery

[BradtheRad]

which battery specification can suite my application.

NIMH batteries are a popular consumer item, and it's easy for a merchant to sell you a sub-standard product with a claim it meets big-time specs. You can expect to pay between $30 and $60 for a 6-cell pack rated 6 Amp-Hours. It is important that you purchase from a reputable source. Shipping costs can add another $10.

NIMH are not indestructible. You need to be careful how rapidly and how long you charge them. You need to be careful how far down you discharge them.

It is still reasonable to consider a 6V lead-acid battery. You might find them carried in a motorcycle shop.

A 12V supply will charge okay, but you must make sure the charge rate is suited to the Amp-Hr rating. If necessary you must limit current with an inline resistor. You must charge for only a certain amount of time, stopping when the battery is full.

 

[ep.hobbyiest]

Thank you all of you.
Means in terms of reliability and life-time NiMH D-cell is better.
So i am going to choose NiMH battery.

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But if i want it to run all for 6 hours then what is current rating i will need?
And how to calculate the current rating require to battery?

 

[Audioguru]

You need 6V at 500mA + 30mA= 530mA.
The voltage of a Ni=MH battery that has 5 cells will average at 6V but will be 7.2V when fully charged and will drop as the battery voltage runs down. We do not know how slow you will allow the motor speed to be.
The capacity ratings (number of mAh) for a battery are from fully charged to almost dead. Your motor will not run for an hour or two at the end of the ratings capacity. That is why I added 50% more capacity in my post #20.

530mA for 6 hours is 0.53 x 6= 3.18Ah. Adding 50% then the capacity must be 4.77Ah.

 

[BradtheRad]

And how to calculate the current rating require to battery?

It is rare that we see max ampere figures for batteries. Different battery chemistries deliver different maximum amounts. And if you draw anywhere near the maximum, it quickly drops.

In general...

AA batteries can provide a few amperes.
Sub-C, probably 10 A.
C, even more A.
D, I have heard amounts over 20 A.

 

[schmitt trigger]

The most difficult part in estimating how many mAHr you'll require is to determine what your motor's average current will be.

The current drawn by a motor is highly dependent of its mechanical load. Is it constant?
Also at start up the motors draw inrush current, so stopping/ starting frequently will increase the average current.
Lastly, a motor's parasitic losses increase with speed even when unloaded.

 

[ep.hobbyiest]

There is no load on motor. That is motor is free running with constant speed.

 

[Audioguru]

I think he means, "And how to calculate the capacity rating of the battery?", not its current rating. I answered him.

Has anybody seen a motor with no load draw 0.5A?? It must be a HUGE motor or it has a lot of friction. Maybe there is air motion inside the motor causing a load.

 

[schmitt trigger]

Has anybody seen a motor with no load draw 0.5A?? It must be a HUGE motor or it has a lot of friction. Maybe there is air motion inside the motor causing a load.

It must be a large motor, indeed.

Anyways, the required battery capacity is simply (time X current), with at least 20% safety factor added to it.

 

[ep.hobbyiest]

No sir. My i have motor with following specification as

Voltage : 6 V
Watt : 2.8 Watt

So i calculated as = 2.8/6 = 0.46 something.
This is motor look like.

 

[Audioguru]

I found an electric model airplane motor that looks like yours with a no load current rating of 0.36A at 6V. It has a stalled current rating of 9.1A.
It is stalled when it starts running and when something prevents it from turning. The stalled current of your motor is probably 11.8A.

I think the size of your motor is a little larger than this one:

 

[ep.hobbyiest]

Here i have attached image with dimension.

 

[D.A.(Tony)Stewart]

Any 6V battery with a >5h capacity should work well for you. Since batteries are rated on a 20h curve, you will get less Ah than rated. Since the motor is rated at ~0.5A at rated torque, 6V you would need >2.5Ah x 5 cells=6V This is based on a guess since the starting current is >10x rated nominal current at speed, due o low winding resistance. The higher Ah batteries have a lower ESR which s needed to start the motor, when the charge becomes depleted.

Any questions? https://www.digikey.com/product-sea...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

NiMH keep getting better, but are only 1.2 nominal so you need 5 cells or 6 V, but they will be much bigger than the motor and cost much more.
thats the way it is.

although NiMH may cost >5x SLA, they are also <20% of the size
SLA start at $10 for 1.2Ah **broken link removed**

 

[Audioguru]

The Energizer Ni-MH battery pack has a crazy price. It costs more than 3 times as much as newer consumer cells that are not connected together. It uses OLD 2500mAh AA cells that were a consumer product about 5 years ago and lost their charge in a month. Newer cells are 2300mAh and hold a charge for 1 year.