Author Topic: Battery questions  (Read 10999 times)

Offline j45on

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Battery questions
« on: March 12, 2011, 02:53:06 PM »
I'm trying to build a remote control video platform to explore the house/garden and maybe further depending on video signal from my arm chair (until i get stuck)
Bassed on this chassis

http://www.dealextreme.com/p/robby-rp5-educational-electronic-robotics-kit-6-aa-45541

I have already squeezed in the radio gear/motor controller and batteries I still have to make a pan and tilt for the camera
and I want to add another battery to power the video transmitter and camera
These draw nearly 400ma how long would a 1000ma battery last ? is there a way to figure out the runtime ?
Jason

Offline John Hill

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Re: Battery questions
« Reply #1 on: March 12, 2011, 03:27:23 PM »
Is that battery rated at 1000ma or 1000maH? 

1000ma just indicates the maximum current the battery can provide but 1000maH would tell me the battery can provide energy equivalent to 1000ma for one hour.  I say equivalent because batteries are usually(?) rated at their 10 hour rate, so a 1000maH battery would be able to provide 100ma for 10 hours,  if you were drawing 400ma from it it would last, in theory, 2.5 hours but in practice somewhat less.
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Offline spuddevans

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Re: Battery questions
« Reply #2 on: March 12, 2011, 03:28:09 PM »
These draw nearly 400ma how long would a 1000ma battery last ? is there a way to figure out the runtime ?

I assume you meant a 1000mAh battery? (that means Milli-Amp-Hours) Battery capacity is usually measured in mAh, and that makes it easy to calculate how long a known current draw will last for a given battery.

In your case your 1000mAh battery with a 400mA draw will last for 2.5 hours, or slightly less as most batteries are overratted on their capacity.


Tim

ps. john just beat me to it
Measure with a micrometer, mark with chalk, cut with an axe  -  MI0TME

Offline j45on

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Re: Battery questions
« Reply #3 on: March 12, 2011, 03:54:43 PM »
Many thanks guys  :beer:  I did not know it would be that simple  :doh:
Yes I meant milli-amp-hours it is this one http://www.active-robots.com/products/power-supplies/00339.shtml
I would have been happy with 40-60 minutes so more is great  :ddb:
Jason

Online Bluechip

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Re: Battery questions
« Reply #4 on: March 12, 2011, 04:37:28 PM »
If you look at the somewhat rubbishy data sheet ..

0.2CA takes about 300 mins to 2.75V
1.0CA takes about 51 mins to 2.75V

So, I would expect about 100 mins or so @ 400mA ... IF
Whatever is dangled on the end will still work at 2.75V ???

Any reputable outfit would give the set of discharge curves ..  :scratch:

BC



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Offline j45on

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Re: Battery questions
« Reply #5 on: March 12, 2011, 04:58:39 PM »
« Last Edit: March 12, 2011, 05:02:58 PM by j45on »
Jason

Online Bluechip

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Re: Battery questions
« Reply #6 on: March 12, 2011, 05:21:50 PM »
Hi Jason

Like everything in electronics .. they will have a max / min operating voltage.
 
Looked at one of the links, suggest you enquire what the drop-out voltage is ..

( One does say 3.3 to 6V ?? )

It may well be that they will still work, except they are not GUARANTEED to work at a somewhat lower voltage.

Not much is going to happen if the volts drop below spec.

Hardly likely to run amok and devour the world is it?  

Just have to put the battery on charge when the kit acts the goat ..


Dunno how much, if any, you're into electronics. But 3.3V is a standard regulator. Not difficult to lash up a PSU from a 6V 2Ah (or larger ) SLA battery.

http://www.rapidonline.com/Electronic-Components/Integrated-Circuits/Voltage-Regulators-LDO/800mA-Low-drop-out-voltage-regulators-LD1117/34991

Some PICs run from 3.3 V. they're still OK @ 2.7V  IIRC ( not confirmed, just seem to think it's correct .. )

BC
« Last Edit: March 12, 2011, 05:28:08 PM by Bluechip »
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Offline andyf

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Re: Battery questions
« Reply #7 on: March 12, 2011, 05:31:46 PM »
I'd be tempted to build a superstructure which would take 3 x 1.2v AA NiMH rechargeables to give 3.6v. You can get 2700mAH (allegedly) versions of those from places like Technobots. I seem to recall (but may be wrong) that NiMH cells hold their voltage until they are nearly exhausted, whereupon the voltage takes a sudden dive.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Online Bluechip

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Re: Battery questions
« Reply #8 on: March 12, 2011, 05:49:30 PM »
Hi Andy

That would be another way  :thumbup:

 :offtopic:

Although I don't have much love for NiMH batteries .... :(

My super duper Bosch 12V drill died after 2 yrs .. battery packs plastic welded but yielded to some butchery

10 batts in each pack, 3 shot in one, 2 in the other ... drill kit with drill, 2 batts, charger, case was 70.

ONE !!! new batt. 53 ??? WTF ???

Crappy (?)  Nu-Tool ( 9.99 )  with one 18V NiCad pack is STILL alive and kicking some 4 years after the demise of the BOSCH ..

End  :offtopic:

BC



 

« Last Edit: March 12, 2011, 05:53:11 PM by Bluechip »
I have a few modest talents. Knowing what I'm doing isn't one of them.

Offline j45on

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Re: Battery questions
« Reply #9 on: March 12, 2011, 06:44:34 PM »
Andy I have some 2700 mah AA,s I will give them a go if the lipo is no good
I have seen AA,s up to 3800mah on ebay
Or go with bluechips suggestion and run a 3.3V  regulator from one of the other batteries
The trouble is I am really short of space in this tiny chassis If I had the money
« Last Edit: March 12, 2011, 06:51:37 PM by j45on »
Jason

Offline andyf

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Re: Battery questions
« Reply #10 on: March 12, 2011, 07:39:07 PM »
Jason, I watched the vid. If that's the size of garden you want your vehicle to roam around, something more than milliamps per hour will be needed.
:lol:

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline picclock

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Re: Battery questions
« Reply #11 on: March 13, 2011, 07:15:29 AM »
Have you considered using the same battery for motive power and video - all the bits running off of one power source ?

This would ease your space requirements, and if the traction battery voltage is higher would allow the use of a small switch mode psu for the camera.

Something like :

http://uk.farnell.com/national-semiconductor/lm2675m-3-3/switching-reg-1a-3-3v-smd-2675/dp/9489800

could probably be made about the size of a thumbnail, around 6-8mm thick. This one works with an input of 6.5 to 40v.

The advantage of this is that the high voltage current is much lower than the camera current (so for a 12v supply a current of 120mA would be converted to 3.3v @400ma), and no power is wasted in heat. Also only one battery to charge.

Hope this helps

picclock

Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline j45on

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Re: Battery questions
« Reply #12 on: March 13, 2011, 04:49:10 PM »
Thanks for all the good info guys  :beer:

Andy I wish my garden was that big but I don't think this vehicle will run outside I tested it today and it manages carpet all right but it is crap on grass and rolls over if i try to climb anything  :(.

Picclock I am using two batteries from my rc helecopter one for drive motors and speed controler and the other for the radio and when my servos arrive a small pan and tilt for the camera.
There should be plenty of capacity left for the camera and transmitter so I shall look into building a 3.3 reg

EDIT: I have had a chance to wire up all the transmitter and receiver bits today and could not get any of it to work  :zap:

 
« Last Edit: March 15, 2011, 12:07:55 PM by j45on »
Jason