| |
In lugnet.robotics.handyboard, Mike Schubert writes:
> > > 1) What is a good battery to use? I don't have 8 nicad batteries.. I
> use
> a
> > > R/C car 9.6V battery pack.. is there some specific need for certian • mAh
> > > values?
>
> > The recommended battery pack I ordered from DigiKey is rated 9.6V at
> > 500mA.
> > So, Don't over kill the board. And I think the motor chip L293D can go
> > up
> > to 700mA (the TI SN754410NE can go up to 1A) (I think I am right)...
> > So,
> > watch out...
>
> Oh, you are missunderstands some "electrical" details :)
> You can use a battery pack with 9.6V and 2000 mA or more if you like,
> because the unit is exactly mA/h.
>
> It means you can get this current over a time of one hour. Or the
> half current over 2 hour's.
>
> The current of the motor chip is only limited of the resistor (from
> motor and the cables to the motor). That the reason why you can't use
> a "big" motor with the L293. The Motor get's too much current.
> (but you can limit the current with a resistor)
>
> hope it helps :)
Yes. Exactly the right point. The two different things to woory about, are the
mA/Hr rateing of the battery (which tells you how long a particular current
can be delivered), and the _internal resistance_ of the battery, which limits
the maximum current it can deliver. Now if you take some examples. The small
batteries used in some 'micro' radio controlled cars, have mA/Hr rateings of
just 500mA/Hr, but are run at currents (in some cases) as high as 15Amps,
giving a battery like usually measured in just a couple of minutes. If shorted
through a system only rated at 700mA, these can blow it just as easily as a
much larger battery. In the case of the Lego battery pack for the 9v motors,
few people realise, that this actually contains a 'self resetting' thermal
fuse, just to prevent a short from damageing anything else (it is a tiny 3/8
inch 'disk' hidden behind one of the battery clips). So the answer if you want
to use a larger capacity 'pack', is to use one as large as you want (provided
it is the right coltage of course), but limit the maximum current with a
similar fuse (or a conventional one, though obviously this has the
disadvantage of needing replacement if too much current is drawn). So
something like a 500mA self resetting fuse, and a 10A/Hr battery can be fine,
when much smaller batteries without the current limit of the fuse, could cause
problems
Best Wishes
|
|
Message has 1 Reply:
 | | Re: Just some questions...
|
| Is there a general guide to what fuse I should have with a certian current? Please excuse some of this if it doesn't make sense, I am learning a lot of electrical concepts as I go... Would the internal resistance of the battery be shown if I measure (...) (25 years ago, 24-Feb-00, to lugnet.robotics.handyboard)
|
Message is in Reply To:
| | Re: Just some questions...
|
| (...) use a (...) mAh (...) Oh, you are missunderstands some "electrical" details :) You can use a battery pack with 9.6V and 2000 mA or more if you like, because the unit is exactly mA/h. It means you can get this current over a time of one hour. (...) (25 years ago, 24-Feb-00, to lugnet.robotics.handyboard)
|
3 Messages in This Thread:
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
