Re: H-Bridge for Small Motors...

Is this because I've forgotten about the actual voltage drop I'll have across the H-bridge? So 2x.7 = 1.4V drop - my motors probably won't even notice, I guess...

But wait - I just read the data*** again - Vcesat is 1.2V so 2*1.2=2.4V... I see what you mean now, I think...

2.4+1.5 = 3.9
3.9/1.5 = 2.6 cells...

So 3 cells are required giving me 4.5-2.4=2.1V for the motors...

Is this correct? Or is there more? I've just increased the heat generated, haven't I... I see heatsinks in my future, yes? B-)

I really didn't want to run the motors any faster than I have to - this is my first chassis (as well as the first electronics I've done for 10 years!) so I don't want anything happening too quick... I guess I can try this and see what happens...

Tim Williams wrote:
1.5V isn't enough to really do anything functional, unless you want to get
old, slow germanium transistors (which would work nicely, depending on what
frequency you want). You really want at least 5V, and to use FETs or
low-saturating silicon (Zetex something or other for example) to drive the
motor from a 1.5V supply.

If you want to stick with silicon, such as a couple 2N4401/03 type deals (a
bit more current rating than those, but along those lines), you'll need more
supply voltage, and you'll take a hit in efficiency, say 50-70% efficient.

If you can go with a, say, +/-5VDC supply for support circuitry, you can use
that to push around some MOSFET gates. MOSFETs should be able to do 90%
efficiency or better.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"nobody" <nobody@xxxxxxxxxxx> wrote in message
news:dtc6mt$486$1@xxxxxxxxxxxxxxxxxx

I want to build (a pair of) H-bridges to drive my motors, described
thusly (from Tamiya kit # 70097 - two FA-130 motors):

* RPM: 6990-9100 (6990 Max. Efficiency)
* Voltage: 1.5-3V (1.5V Recommended)
* Amperage: .66A

Assuming I'm going to go for the recommended 1.5V, geared down lots and
with small wheels (don't want the little beasty to move faster than I
can run!), I can get TIP31B/TIP32B - I assume that these will be
somewhat overkill, but will work correctly? Considering they're rated
for 3A, I shouldn't be needing heatsinks?
.

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