Powering Nema 17 + Uno + Easydriver with Battery.

I've got a motorised camera slider running nicely on AC but need to have it portable. Can someone recommend a suitable battery setup for this application? I had it working on a 6pack of Li-ion AAs with a 5v servo but it was too loud. Changed to 5v stepper but not enough torque so i decided to go for a Nema 17 which has plenty.

Under the impression that all Nema 17s were 12V, and figuring the arduino can regulate down to 5V, I figure I need a 12V battery that I can split to power both. I searched ebay for 'Lithium 12v Battery' and bought one of those cheap chinese things wrapped in blue plastic. It fits perfectly size wise, has DC plug that fits Uno and a charging socket. When I hooked it up this way with the AC charger plugged in at the same time, everything works awesome. The stepper has so much torque I have trouble stopping it with my hand. Problem is when I pull the AC power, it only works for a minute or so before failing. It seemed to work for a while the first time I charged it but now it's got nothing even after charging all night. (I pulled this battery apart to inspect and it seems to be a series of waver like cells bodged together and a whole lot of empty space. I very much doubt the 3000mAh printed on it.) I think there's too much current draw for this dodgy pack.

So, I need something like this, but that actually works. I'm even more confused now as my stepper apparently has these ratings.

2 Phase bipolar 4 wires Rated Voltage 2V DC Rated Current 1.2A

2V is far from 12V that i originally thought, though it works great at 12V. So, should I use a pack of AAs? Will they provide enough current? What voltage should I aim for considering the stepper rating? Are there other, better made battery packs like the one I bought from ebay, but that actually work?

Chunky SLA type things like motorcycle battery are not an option. It needs to be slim and flat and not too heavy.

You can use a 2000mAh 1S LIPO. http://www.hobbyking.com/hobbyking/store/__18558__turnigy_2200mah_1s_20c_lipoly_single_cell_.html

FYI, "20C" means it can discharge at the rate of 20 x 2000mA = 20 x 2.0A = 40A, (2/40=0.05 hours = 3 minutes at 40A)

2.4A/2A= (0.833*60=50 minutes at 2.4A

Ok thanks, that looks interesting. So do you think 3x @ 11.1V or 4x @ 14.8V considering they will likely almost always be in some state of discharge?

Eg. when I tried my 6xAA pack (~7 - 8V), the stepper moves slowly and stutters if it moves at all and my I.R proximity sensors don't trigger.

For anyone looking at the blue ebay packs, this is what's inside. Strangely they say 3.7V on one side and 4.2 on the other.

I'm assuming/hoping that the cells linked above by raschemmel will be better.

FYI the "discharged" voltage of a lipo cell is 3.7V. The "charged" voltage of a lipo is 4.2V..Thus, the charged voltage of 2S (not 2x) is 8.4V and the charged voltage of a 3S is 12.6V and a 4S is 16.8V.

You need a little more knowledge about stepper motors. Nema 17 only defines the physical size of the front face and the screw-hole positions. It has nothing to do with the electrical characteristics.

The important number for stepper motors is the current. You haven't said what stepper driver you are using. Hopefully you are using one (such as the Pololu A4988) which can be adjusted to limit the current and can then be supplied with a high voltage without damaging the motor. The high voltage is important because it allows the full motor current to be reached quickly each time a new pulse is sent. If your driver can't limit the current then you are restricted to using a low voltage that won't cause too much current to flow in the motor.

Your choice of batteries needs to take that into account. You need batteries that can provide the required voltage and which can provide enough current for however long you want the motor to operate. If you are drawing 1.2A continuously you will need a substantial battery - probably 2000mAh or more - just to run for an hour. You don't want to run the battery flat.

The other important thing is how is the Arduino powered. It would be best if it had its own separate battery so it is not affected by the motors.

...R

TijuanaKez: Under the impression that all Nema 17s were 12V, and figuring the arduino can regulate down to 5V, I figure I need a 12V battery that I can split to power both.

NEMA17 is the size of the motor physically and the spacing of the fixing centres, nothing whatsoever to do with voltage or even what type of motor.

Google would tell you that.

A 1.2A bipolar in NEMA17 format is a low impedance bipolar motor and should be driven by a chopper-driver from as high a voltage as you need to get the performance you want (higher voltage = faster top speed), although insulation limitations probably limit you to 48V for cheap NEMA17 steppers.

24V is a reasonable choice. 12V is rather low if for instance you are driving a lead-screw, but may be OK if driving a belt.

Chopper drivers take less current from the supply than they supply to the motor because they are DC-DC buck converters using the motor inductance. When the motor is stationary of moving slowly the current pulled from the supply is even less. You can estimate this from the power consumption of the motor and assuming the converter is 80% efficient or so.

Ok I've had a chance to come back to this project. Thanks for all the info. Since got my head around the stepper hole spacing thing and feeling a little dumb for some comments! So specs for the stepper I have is

200 steps per revolution (1.8 deg/step) 2 Phase bipolar 4 wires Rated Voltage 2V DC Rated Current 1.2A

I have wired up a separate DC jack that is split to feed the Easydriver and the Uno. With a 500mA 12V power pack, everything works perfectly ( relying on the Uno's regulator for 5V) Just need to decide on a portable battery solution that will provide similar power, ideally, rechargeable by plugging in the power pack.

Size and price wise, the cells suggested by raschemmel would suit great. I'm about to press buy but thought I better double check that I'm thinking straight. Would they be appropriate power wise? The spec is

Minimum Capacity: 2200mAh Configuration: 1S / 3.7v / 1Cell Constant Discharge: 20C

So 4 of them would be 14.8V. (but I'm still confused if that's charged or not) Sound like it could do the trick or should i go for 5 or 6? Too much voltage for Uno then?

nS CHARGED VOLTAGE

3S 12.54 4S 16.72 5S 20.90

Ok thanks for that. So how do you think 4S would go with the Arduino DC supply?

NO WAY ! The max input for the EXT DC BARRELJACK is 12 V

Input Voltage (recommended) 7-12V Input Voltage ([u]limits[/u]) 6-20V

17V is within the limits but NOT recommended due to the overheating of the 5V regulator to dissipate the excess voltage.

3S is the maximum for the ext dc input of the arduino UNO.

Don't forget a fuse if powering from a lithium/LiPo, any circuit short and these packs can put 100's of amps through your circuit. This applies to lead-acid batteries too. Other battery types tend have enough internal resistance to get away without a fuse

In case you are not LIPO experienced: https://www.youtube.com/watch?v=-DcpANRFrI4

Ok LiPOs definitely sound like they need some extra forethought.

If I wanted 4S for good stepper power, would a simple dropping resistor sort the arduino? ( I never quite could get my head around selecting right ohms when current is not constant)

Or would I need another regulator? I originally bought some of these http://numato.com/7806-6v-voltage-regulator-breakout-board for the purpose but since read that regulators are inefficient and not a good choice for getting the most out of batteries.