Trying to figure out what kind of DC Power Source I will need.

😀  Wow, that robot looks COOL! I hope you keep us informed of your progress and I can't wait to see it working!

@dubbadan 

I glad you like it.

Thanks to everyone else who is trying to help - Bill

Ok this is me thinking outside the box so it's ok to tell me if I'm crazy.

What about using a power tool battery?

Like this one -

https://www.ebay.com/itm/166320027173

The 18V 12Ah Version. I am sure I could fit the entire battery into the robot, and not take the battery apart at all. Yea I would need some kind of power connector, but I think that's doable. Then I could just take the battery out put it in the correct charger and I'm goo to go. I could over time even buy another Battery or two. Hell I might even buy a cordless drill to use (lol).

Info for anybody who needs to catch up:

I need a power source that can handle 7Amps max load and run for about 90 mins to 120 mins at 12Volts.

Tell me what you all think -

Bill

@greendragon The math works, you are asking for 7A at 12V for 2Hrs or 168 Watt Hrs. The battery claims to have 18V at 12AH or 216 Watt Hrs. You will lose a little when you buck the 18V to 12V but there should still be enough.

HOWEVER, I am very skeptical about those batteries. For LiIon they are awfully big. Does not make sense. But at that cost give it a try and let us know. Run the robot until the battery dies to determine the capacity after charging it to 100%. 

Obviously you will need the proper charger for the battery.

HOWEVER, I am very skeptical about those batteries. For LiIon they are awfully big.

Just to clarify you statement here -

1 - You think they are over estimating the voltage and amps?

2 - or that it's just too much power for a cordless drill?

If it's "it's just too much power for a cordless drill" I would say your right if they only used these batteries in one device, but don't forget that they are going toward using one battery for all types of power tools (saws, j saws, etc..) and they do need more power and amps for longer use.

My thinking on this battery is that they sell it in America and they are selling to a big audience (people what want and use power tools) and so the odds are good that they would have to use sturdy well made battery's an not the knock offs as that would get then into trouble fast.

Bill

@greendragon Sorry, but power, as well as amps, is drawn by the device. You could connect a battery with 10x the AH, which would make no difference other than running 10x longer.

I just found the picture with the dimensions. I withdraw my comment regarding size, they seem correct.

Remember they are selling at least three different batteries on that page, all 18V but 6AH, 7AH, and 12AH. Buy the charger while you are at it. Use the drop-down selector to pick. They are out of 12AH bundles, but the standalone charger is only $19. That is an extremely low price. I would not buy it.

BTW, it is not made in the USA; it is undoubtedly made in China.

it is not made in the USA; it is undoubtedly made in China.

I thought everything was made in china (lol). Seriously though there are many great products made in China as well as every other country in the world. You just have to sort out the good from the bad nowadays.

I keep going over in my mind if I should take the battery apart, and build a smaller battery using a BMS and then I could use a plug in/usb charger? What are your thoughts on this idea?

Bill

@greendragon Just exercise caution when taking them apart, they can bite. Taking it apart will at least reduce the volume, but at what cost? You could reuse the BMS inside the battery pack. Not sure what you mean by plug-in/usb charger. Each battery chemistry requires a specific charge profile. The worst case is an explosion or fire. Do NOT mess with charging, get the right one and a quality one.

Each battery chemistry requires a specific charge profile. The worst case is an explosion or fire. Do NOT mess with charging, get the right one and a quality one.

Wise words. Point taken - Bill

@greendragon 

I was always conscious of the need to have a battery charger circuits suitable for any battery I used. This is the battery I used in a robot project. It had built in electronics as part of the battery.

https://forum.dronebotworkshop.com/2022-videos/safely-using-lipo-batteries/paged/2/

I noticed that all robot vacuum cleaners have special circuits to control the charging of batteries and include sensors within the battery pack to monitor I assume temperature.

Hi @greendragon,

   I can't be sure of anything looking at a screen photo without any dimensions, but my 'guts' are suggesting this might be a 'too good to be true' case.

In terms of energy storage density ... the amount of energy you can store in a given volume is roughly determined by the technology. The 'best' 18650s Li-Ion cells, of a given chemistry variant, will have been optimised by reputable companies, and gives a rough benchmark.

Others may have better data, but I would suggest that an 18650 cell can probably comfortably manage 3.6V 2.5Ahr, maybe stretched up to 3.0 Ahr ... so let's assume 3.0 Ahr for this discussion.

For 18 V 12 Ahr, This would need 5 cells in series (5 * 3.6 V = 18V) for voltage, and 4 columns of (5 in series) cells in parallel to achieve 12 Ahr  (4 * 3.0Ahr = 12.0 Ahr)

So the battery would need to consist of 4 * 5 cells, namely 20 cells.

Does that box have the volume for 20-off 18650 cells? Is my 'per cell' data flawed?

BTW 18650 means 18 mm diameter cylinder, 65 mm high.

Just a thought..

In addition, beware of the current supply ability .. i.e. how many amps can it output continuously? Hand tools like drills are often only used for a few seconds at a time, allowing them to cool down. Continuous use for an hour is a different situation. Cheap cells tend to have higher internal losses, produce a lower voltage under heavy load and create more heat, all factors that are not specified in the advertisement.

Best wishes and please take care, Dave

@davee I don't often get a chance to help Dave, but this time, I think I can. You somehow missed the photo with the dimensions. They are 7.5cm x 11.6cm x 8.2cm for a total volume of 713,400 mm^3. There will be something less than that available for the batteries as there are electronics and mechanical systems in there as well, but 20 18650 arranged in 4p 5s only needs 421,200 mm^3 so lot's of room for the BMS etc.

The batteries are standing up with five along the long dimension and four on the other.

LiIon 18650 is between 2600 and 3500 with a good average of 3000mAh, so 4p gives 12000mAh or 12 Ah. It checks out.

The following is my 2 cents:

I have been watching a few you-tubers taking these types of batteries apart, and believe it or not They have 10, 15 and even 20 cells in them. So yea it's possible, but I will not know the truth until I buy the thing. Have to wait till after Christmas. The only thing I know for sure is when buying 18560 cell is that you are taking a chance. Period. I am just trying to min-mise that risk. Unless you all know where I can but good 18560 cells at $5.00 USA or under.

Bill

@greendragon We know there are 20 cells, simple math. Once you find a reputable supplier, you need to decide between two physical sizes, one is flat top and the other is nipple top. Then decide if you want a battey with a built-in protection board (mini-BMS) or not. Now from that list pick the discharge size you want. Vape batteries have a very high discharge rate, I have seen 30 AMPS. You likely do not need that.

The good news is the cost (I didn't shop around) is $4.50 for 2 2600mAh protected nipple top (slightly longer) from https://18650canada.ca NOTE the similar site but ending in .com has MANY complaints.  Since shipping especially of anything Lithium is expensive, you will need to find a local reputable supplier. Use this Canadian site to find what you want them find a local supplier of the same part. WARNING, these batteries are the most often faked parts I see. Buy one and load test it. That may mean you need to buy a load tester. This one is made by DROK, a brand I have used with no problems, but only goes to 3A if that is a problem https://amz.run/7U8A . This is another tool I use https://amz.run/7U8B , and also this expensive but very useful beast https://amz.run/7U8C . It not only goes up to 6A, but has the ability to display data on phone or computer. Check amazon reviews, and the docs etc are at https://forum.avhzy.com/forum.php?mod=viewthread&tid=1 may not be in English tho.

@greendragon I forgot to add some capacity checkers this is one I have https://amz.run/7U8Q  

I also have https://amz.run/7U8W and this one also https://amz.run/7U8X