Here is an interested by option.

Bob

 

I wasnt aware of the CR123A size. I think I will try those with the charging board mentioned. Thanks for all your help, I think this should work.

 

The charging is done with a standard phone charger. They provide a splitter that can charge 4 at a time. You might also be able to purchase a single one, I didn't look further.

Bob

 

Are No-Name-Brand EBL batteries as bad as their Chinglish?

 

You could still read it though right?

 

Hi,

I am making a small robot and want to select the battery that gives me the most prolonged use at the lowest price and fits into the smallest space allowable. It only needs to power the drive mechanism and no micro controllers etc.

I have already made the mechanical parts of the robot (e.g., gearing).

When I run the robot with a lab power supply, the wheels turn as I would like from 3V, showing as 130mA. When I resist the rotation with my physical strength, it goes up to around 230 mA. If I increase the voltage, the wheels spin faster, but I don't think I need this (although it would be allowable if it offers some advantages related to the above points). From observing it, I can see that anything above 5V would be too fast for what I need.

The motor was taken out of an sg-90 servo. I think it is a 5V motor, but I could be wrong. This motor is used because I have a lot of them on hand, so it is convenient for me to use them rather than buy another. For this practical reason, the choice of the battery should be selected to fit this specific motor.

I got some cheap CR2032 3V lithium cells from a local discount store (pack of 20 cost me €5). I can't see a mAh rating on the packaging. From Google, my understanding is that it is typically around 225 mAh. These are very cheap batteries, though, so I don't know if that would also apply to these batteries or more premium versions of the CR2032. The robot motors do not turn with one coin cell, but it does with two coin cells placed on top of each other.

The motors spin for about 30 seconds, then the robot motors sound like they are struggling, and it stops shortly after. I thought that the batteries had run out, but if left for a few minutes, the process can be repeated. I can see that the voltage goes back up. Do you know what the issue could be? If they are 225 mAh each and my robot only draws 130mA, should it not run for several hours?

If I used a 3V regulator, would this increase the runtime, or would it just add inefficiency and unnecessary cost?

Do you have any other suggestions about how I might be able to increase the runtime?

I might also use AAA batteries instead, but the rechargeable versions are pretty expensive for what I need. The CR2032 has a rechargeable version called the LIR2032, and I am thinking of using those if I can increase the runtime to at least 10 mins of use. I can see that these are also very cheap.

Many thanks for your help

Hi there,

These kinds of applications are usually all about energy density with the price tag taking a back seat.
In other words, you should not worry about price so much and go with the highest energy density which means the most power with the least weight.

The best is probably Li-ion because right now they have high energy density and they are not super expensive either. They are also rechargeable, so you dont have to keep buying new batteries. You do need a proper charger though, but if you are not in a hurry to recharge these come pretty cheap also these days. The fast charge chargers are a little more expensive, but it's a one time investment.

Because battery technology is so important these days there is a lot of ongoing research today so there are a lot of brand new chemistries about to hit the marketplace. I havent seen any yet but there should be soon.

 

2400 mAh from a CR123A sized cell isn't real; knock a zero off that capacity and you'll be closer to the truth. Realistic RCR123A cell capacities seem to range from 400 mAh to 750 mAh.

 

2400 mAh from a CR123A sized cell isn't real; knock a zero off that capacity and you'll be closer to the truth. Realistic RCR123A cell capacities seem to range from 400 mAh to 750 mAh.

The EBL brand of CR123A battery says 2400mWh because they know that people like you will think mAh.
2400mWh/3.7V= 649mAh.

 

If saety is an issue because kids will be playing with the thing, add a series fuse so that if there is any overload the fuse will open and everything will stop. Inconvenient but safe.And the little fuses do work nearly instantly, at least that was my experience. Not cheap, but very effective.