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Topic: Powering arduino with 4.8V NiMH battery (Read 5627 times) previous topic - next topic

larryd

I fully agree with using a SMPS buck converter.
Use one and get on with your project.

No technical PMs.
The last thing you did is where you should start looking.

anvoice

I agree the buck module is a nice suggestion, and I'm not trying to discredit it, but the robot has 16 total leg servos, plus 2 servos for a camera, as well as the board and sensors. Assuming all 16 servos stall at once, for example (unlikely, but possible scenario), that's an 8A power draw. That's without the amps or so the board and sensors will be using (the ESP8266 wifi module alone, which I'm planning to use, takes about 300mA I believe). So I'd need quite a bit of a safety margin or a lot of buck converters. I did find a 10A converter on ebay for a reasonable price, but it's too big and probably too heavy to fit on the small robot. At that point I'd really be better off getting a small separate battery for the arduino, I just wanted to avoid having to go that route.

larryd

This is the highest amperage version I've used.
http://www.ebay.ca/itm/DC-DC-Step-Down-Power-Module-4V-38V-to-1-25V-36V-5A-LED-Voltmeter-Adjustable-/371358493678?pt=LH_DefaultDomain_0&hash=item5676b0ebee

All the versions I have used are short circuit (you could call this stall current) protected.

I see there are 12 and 15 amp versions on eBay.
.

No technical PMs.
The last thing you did is where you should start looking.

DrAzzy

Yeah, that is actually a pretty good point on just using a buck or boost converter.

12A, $5 shipped. http://www.ebay.com/itm/DC-DC-CC-CV-Buck-Converter-Step-down-Power-Supply-Module-7-32V-to-0-8-28V-12A-EC-/221670461819?pt=LH_DefaultDomain_0&hash=item339c96d17b


Actually, you could use a buck/boost converter to supply the arduino with a constant comfortable voltage, while running servos straight off batteries....

$2 shipped buck/boost http://www.ebay.com/itm/DC-DC-Boost-Buck-Converter-Step-Up-Step-Down-Supply-Module-3-35V-to-2-2-30V-HG/271720088700?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D32237%26meid%3Dff97540d481642989f28d171bc93103a%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D290833291375&rt=nc

No endorsement of those specific vendors - there's a huge number selling same units and similar ones.
ATtiny core for 841+1634+828 and x313/x4/x5/x61/x7/x8 series Board Manager:
http://drazzy.com/package_drazzy.com_index.json
ATtiny breakouts (some assembled), mosfets and awesome prototyping board in my store http://tindie.com/stores/DrAzzy

anvoice

The step-down converter is too bulky to comfortably fit on the robot chassis. It's a fairly small machine.

Yes, that was along the lines of my original question. The step-up converter might be a good solution, it's a lot smaller since I only need enough current for the arduino, thanks for the tip.

Still, it'll take precious space and add weight, so if anyone happens to know whether the arduino itself might be fine with the 4.8V (as mentioned, a bit higher at peak and probably lower towards the end) I'd appreciate hearing it, it'd make the whole setup easier.

Wawa

#20
Jun 26, 2015, 06:59 am Last Edit: Jun 26, 2015, 07:03 am by Wawa
Step-up converters have a different behaviour than stepdown converters.
Read up about noise, short circuit protection, dropout voltage, and efficiency before you choose one over the other.

Personally I think higher voltage batteries and buck converters that are just ok for the job (not calculating total stall current) are the best overall choice.
An efficient 5volt/2.5A buck converter should be the size of a postage stamp.
Use two if you have to.
Leo..


anvoice

It's pretty difficult to grasp everything at once, didn't know there's a difference in behavior. Would something like this work?
http://www.ebay.com/itm/DC-DC-Converter-Mini-Step-Down-Module-BUCK-Adjustable-3V-5V-16V-for-RC-Plane-/371295065523?pt=LH_DefaultDomain_0&hash=item5672e915b3

Very small, 2-3 should provide enough current, efficiency characteristic for this DSN-mini-360 module is listed as 96% max. Not sure if there's a catch I'm missing.

I also ordered a XL6009 step-up board just in case, no idea about what it's noise is. Efficiency is 92% top but with an amp or so of current needed it's better than losing 4% of 5 amps. I feel like worst case I might be able to boost the signal up to 7-9V, then run it through the arduino power jack where the regulator will take care of the noise.

Need to figure out which of these setups will be more efficient so I can choose the battery.

Wawa

I would try those small buck converters with a 2C LiPo (7.2volt).

Boost converters can be noisier with a small voltage difference, and buck/boost could be less efficient.
Lineair regulators are not very good at removing switching noise.
Capacitors and inductors are.
Leo..

anvoice

I'll get the step down converters, they'll be good to have around in any case.

After doing inventory of available LiPo/LiFe batteries, I noticed that all of them with reasonable capacity are a bit big to fit the robot chassis. The best thing I could find was a NiZn, which has smaller dimensions for the same capacity. Might have to give the step-up converter a try, if that doesn't work I'll make a filter for it, and if that fails switch to a step-down.

Thanks for the help, I appreciate it.

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