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

1. Use Lipos

2. Buy A power tool battery, and take my chances.

3. Use 189650 by buying them, or salvage them and build my own battery.

4. SCREAM, and RUN AWAY....

The use of Lipos is OFF THE TABLE. (MY CHOICE)

Bill

@davee There is so much in your post I could quibble with, but it's been a long day and you are a master at saying little with lots of words so I am refusing to play anymore today.

This part, though is downright weird

As for the small cells which I suspected existed for mid-range power tools, and you found a reference to a design nominally 10 mm shorter than my wild guess, I suspect they are a version of the most common/well-established chemistry which uses cobalt as one of its 'ingredients' but is usually just referred to Li-ion. i.e. apart from being about half-size, half-capacity, etc., they are probably the same as their ubiquitous full-sized brothers.

I didn't 'find' anything, it's a STANDARD size!!! The international standards fiolks got tired of trying to assign alphabetical designations and did the smart thing naming the cells after their nominal width and length (yes, they did not change the 65 part when they added a few more mm for the PCB under the anode.

There are two formulations often called LiIon, and one is Cobalt-based, the other Manganese. We like Cobalt since we don't live far from Cobalt Ontario. Guess what they mine there? (it was silver, the Cobalt was waste)

Your last sentence totally confuses me. If I didn't already know you, I would think you addled, so either you misspoke, or I am misunderstanding. What are full-sized and half-sized?

I agree I should not have said BMS, as that device does a lot more, but it sent the appropriate message for the audience (other than you). The cells with the PCB are called 'protected' for a reason. It is not as you so famously like to say, marketing, it's just good engineering and producing a better product because it is safer.

Enough for now. Let's help the OP, not try to see who has the biggest xxxx. I think I gave him the answer, it's up to him now as the cost is significant.

@greendragon OK, then I and likely no one else can help without knowing the absolute max size of a battery compartment you have and your country of residence, as that can dramatically affect the cost of parts.

@greendragon I found this on Amazon.ca https://amz.run/7UPT dimensions are in 2nd pic down; they are   10.23 x 5.23 x 8.95 high, but add some to that to get cables attached, etc. Because it is LiFePO4, it has no liquids so it can be mounted in any orientation. I have even seen installations with the battery upside down.

I think you may have more space vertically, so do you have 8.95 x 5.23 and 10.23 high?

@greendragon How about this, https://amz.run/7UQ5 6V (will need a boost converter) 6Ah but will be reduced to a little less then 3 due to the V boost, but dimensions are 70mm x 47mm x 100mm tall. That is 2.76" x 1.85" x 3.9 inches tall.

This is the safest and lightest lithium chemistry. Just make sure you attach a disaster fuse (check solar suppliers) DIRECTLY to the positive post sized for worst case normal draw but will protect against a direct + to - short., and then use normal fusing to each motor circuit based on insulation specs and peak motor draw (@davee might be able to add a factor to the peak, as in 110% of peak) also consult online charts for wire AWG, peak expected amps, and insulation type.

My RV disaster fuse was 400A DC at 12V, my individual circuits were more like 80A for the hydraulics, 50A for main 12VDC leg, then each individual circuit was fused by the factory. If you think 400 is high, consider what that is equal to on a 120V AC circuit, only 40A or two air conditioners starting at the same time. Not likely, but it could happen. My inverter was only rated at 3,000W, 2400VA with a peak of 6,000W. My inverter was programmed with time and current thresholds that would have shut it down long before the disaster fuse blew but the disaster fuse was for the dropped wrench across the + and -. Since my busses were covered in plastic even that was unlikley.

For a charger, it is best if it is programmable, but a inexpensive charger designed for LiFePO4 will be ok, and an AGM will do in a pinch. Just make sure to NOT trickle charge, and store at about 70% capacity. 

Hi Ron @zander,

RE:

This part, though is downright weird

As for the small cells which I suspected existed for mid-range power tools, and you found a reference to a design nominally 10 mm shorter than my wild guess, I suspect they are a version of the most common/well-established chemistry which uses cobalt as one of its 'ingredients' but is usually just referred to Li-ion. i.e. apart from being about half-size, half-capacity, etc., they are probably the same as their ubiquitous full-sized brothers.

I didn't 'find' anything, it's a STANDARD size!!!

I think you posted this...

And in my book, 16340 is fairly close to half of 18650.

... and which is what I meant.

I agree there are several other variants of the precise chemistry, including one using manganese.

https://en.wikipedia.org/wiki/Lithium_ion_manganese_oxide_battery

I think some of these variants have been adopted by car manufacturers, but I am l not clear how many of these are seen in our usual marketplaces. In principle, manganese is much easier and cheaper to source, than cobalt, but sourcing cobalt is still seen as a critical limitation. Unfortunately, most of the adverts we see do not list the precise chemistry, (with the exception of LIFePO4, whose different voltage, etc. characteristics make it obvious.) Sorry if I have understated the number of variations.

Best wishes,

Dave

@davee Ok, now I see how I confused you. Sorry, did not mean to. It is just a hunch on my part, but I think there are dozens of ddlln cylindrical cells on the market. Many are special purpose in that they are for a class of consumer product or industrial use sold in sufficient quantities to warrant a specific sized battery

In my house I have 18650 plus the longer protected version, 14500 and I think I am missing another. I am aware of 16340, 21700, 26650 as well. For a complete list look at  https://en.wikipedia.org/wiki/List_of_battery_sizes there are a lot more than you may have thoght.

Hi Ron @zander ,

  Long day indeed, and my eyes are tired ... but I can't spot a reference to this product

How about this, 6V (will need a boost converter) 6Ah b...

Did it drop off, or is it just me again?

------------

I did know there were lots of cell sizes defined and possibly adopted by OEMs buying by the million... how many make it onto the open market for us to easily buy in small quantities is less clear.

-----------

As for estimating currents, that is a bit of a nightmare with stepper motors unless you have the 'full story', which as @Inq has also been explaining, is not straightforward.

The controller/driver chips usually have a 'high' voltage available, but control the current by PWM drive, using the natural inductance of the stepper motor windings to act like a buck converter

... and a buck converter you may remember is about like a transformer .. e.g. 20V 3A input could become 10V 6A output, if it was completely lossless. Of course, there are always losses, but a 2A (say) current in the windings does not automatically imply 2A drain from the power supply.

Hence, with these multi-motor systems in particular, I advise the other person to try to do some measurements before buying batteries, embedded power supplies, etc. , as there is substantial risk of buying much too high a capability (and dwarfing the real project as well as possible near bankruptcy), or  any amount small (so that it doesn't work)

--------------

Best wishes, Dave

@davee I forgot the link https://amz.run/7UQ5

I did mention there would be some loss.

As to his amperage estimates, they were his with Dennis @inq in support. They estimated 6A total. So that tiny 6V 6AH $40CDN / $30USD battery should give him 30 mins. Buy two or 3 and a decent charger and he will come close to continuous power.

Go to bed Dave.

Hi Ron @zander,

  Thanks for the kind wishes.

  The current requirements thoughts were more associated with your suggestion of the need for a boost converter and its spec, which included my name being dropped.

Batteries are usually tolerant of occasional short, moderately higher, current spikes, providing they do not overheat the battery or trip a protection circuit, whilst boost or buck converters can hit relatively hard limits for a number of reasons, including magnetic saturation, protection circuits tripping and potentially in the worst cases where protection is inadequate, magic smoke.

Remember, Inq's great family of bots (generally) each have two identical motors performing essentially the same role .. this thread started with a description of 13 motors of 4 different types ... estimating the current demand under all conditions, without being very familiar with its design and usage, is going to be tricky at best!

Furthermore, I haven't checked, but I suspect Inq's current estimate of 6A was based on more than 6 V battery/supply voltage. Remember, a boost converter supply output of say 12V at 6A will need more 12 A at 6V, whilst the battery you suggest is 10 A max. I am not saying the battery is too small, just that the error margins on present estimates of power demand are too wide for an accurate determination and decision.

Hence, my advice is to take some decent measurements - they do not need to be very precise, say to within 10% will do, as a margin must be added on for the unexpected. They should cover all cases of usage, and ideally include some scope measurements to look for spikes, although in these circumstances, the risks of not using a scope are probably acceptable.

Best wishes and take care, Dave 

@davee, I didn't notice the 10A limit. With some losses going through the boost converter, we will be some % short of 12V 5A. PLUS, I just noticed the following. Not sure what they are talking about but it sounds like more trouble for this use case.

The output voltage is output directly from 2S Li-Ion battery by through the PCM, so the output voltage is not constant.

I just noticed that battery is probably full of air as it is just 2S1P of 32700 3.2V 6000mAh cells. They are 32.2 x 70.5 +-0.3mm. I am going to recommend he build his own battery of 4S x 2P giving him 12.8V 12Ah and peak 20Amps. He just needs to buy some tools, and BMS as well.

Hi  Ron @zander,

  I agree that 4 cells in series for 12-14V is probably the sensible minimum for driving steppers.

  I am not suggesting the present estimates are wrong, but I'll leave considering the current requirements until I have seen some current measurements. Accurately estimating 13 motors' combined appetite feels too much like shooting blind, for my liking.

Best wishes, Dave

@davee I agree; I don't have a gut feeling for those motors, but I took Dennis's (@inq) word as he has a lot of experience.

Posted by: @davee

↑

I agree that 4 cells in series for 12-14V is probably the sensible minimum for driving steppers.

Posted by: @zander

↑

@davee I agree; I don't have a gut feeling for those motors, but I took Dennis's (@inq) word as he has a lot of experience.

I haven't had a chance to go through the thread if a more detail spec has been given... I've just perused the OP and saw the picture of 42... Way cool @greendragon! 😎 Please don't get discouraged with any of the banter.  We all get in purist modes sometimes and argue with each other.  Any of the suggestions will work. 

Not knowing how things will be driven or configured, there is no reasonable way to make an estimate.  I see 8 wheels on it, so @greendragon stating (7) Nema-17's ain't computing. 🤣 So, I'm taking a WAG that 4 are motive.  The other three '17s and Nema-8, Gear reduced ones are for moving appendages.  Was there an all-up-weight estimate???  I thought I saw someone say erector set, so lot's of steel... I'll guess around 2 or 3 kilos.  The selection of Nema-17 only handle up to 1A and I'm wondering if that's going to be enough Torque/HP to drive something that large and heavy.  Many here know I'm a lead-foot and "too much torque / HP" rarely comes out of my mouth.  Me... I'd use something like two of these 84 oz-in puppies.  

 So... here is a back of the napkin.

Stepper 101

@davee - Remember in one of our educational threads I was wondering how why my bench power supply was showing such low currents... yet my in-line volt meter (reading current) was showing the coil currents were up close to driver spek???  Anyway, I did a lot more tests and I finally clicked with something you said. 

Many people starting out with steppers see the specs and either see a voltage like ~3V or do the V = IR thing with the resistance and say... I only need a 3V battery for these things.  NO!  But... those calculations DO hold for how much is being used.  So even though the power source may be 18V in this case, the motor is only seeing 1.0A at the 3.7ohms (these stepper's spec)... thus at full-tilt, they're only using 3.7W!

So if 42 is run at full throttle, waving everything it has...  we can take a WAG at full-load current being around 3.7W x 7.  The little Nema-8 steppers calculate out to about 1W x 6.  Assume some waste for the drivers and a meager bit for the Mega and support electronics and I WAG around 40W max load.  With the proposed (last I read) Makita clone of 18V x 6Ah / 40W = 2.7 hours! run time.

Any judicial use of disabling idle steppers/drivers and 3 or 4 hours might be a more realistic time.  If this is a "Science Faire" type bot... it might spend most of its life just standing still and waving every so often.  If the all other drivers are disabled... it might run continuously over a weekend while he waves to the audience, talks, blinks lights.

I'm looking forward to seeing it go.  

VBR,

Inq

@inq to catch you up, the fake Makita battery is waaaay too big to fit into the 3" wide opening. I found a much safer LiFePO4 that is 32mm wide so a 4s2p will need 64mm or 2.5" and they are 2.75" high. The opening is 5+" deep so half that space is available for a BMS and the extra height for the Mega etc. The 4S2P tops out at 20A with a 12Ah capacity.