2-Batteries

Martin Gregorie wrote:
wrote:

This is great discussion. I was doing a bit of research myself (it has
been over 10 years since I did any HW design, so am pretty rusty).

Another option that sounds even better is to use the new chips designed
for exactly this to control DirectFETs. That way the voltage drop and
power waste will be significantly reduced with very little additional
cost. The chips I were looking at were IR5001S:
http://www.irf.com/product-info/data...ta/ir5001s.pdf or LT4351:
http://www.linear.com/pc/productDeta...,C1079,P21 73



I have used DirectFET stuff in robotics and found them to be very
reliable and very simple to design with.

My biggest problem is all these components are only available in
surface mount these days and I have never tried to build a circuit
using them.

That should be easy enough to do with a pair of suitable power MOSFETs
and an LM358 dual op-amp to control the MOSFETs. If I don't split my
supply (see earlier post) I'm thinking about making this type of circuit
this because the voltage drop in the MOSFET will be very small.

Size isn't an issue - suitable MOSFETs are in TO-220 type packages and
the LM358 is an 8 pin DIP package.


How much lower thatn 0.3V drop will the MOSFETs get you?

Gary Emerson wrote:
Martin Gregorie wrote:
wrote:

This is great discussion. I was doing a bit of research myself (it has
been over 10 years since I did any HW design, so am pretty rusty).

Another option that sounds even better is to use the new chips designed
for exactly this to control DirectFETs. That way the voltage drop and
power waste will be significantly reduced with very little additional
cost. The chips I were looking at were IR5001S:
http://www.irf.com/product-info/data...ta/ir5001s.pdf or LT4351:
http://www.linear.com/pc/productDeta...,C1079,P21 73



I have used DirectFET stuff in robotics and found them to be very
reliable and very simple to design with.

My biggest problem is all these components are only available in
surface mount these days and I have never tried to build a circuit
using them.

That should be easy enough to do with a pair of suitable power MOSFETs
and an LM358 dual op-amp to control the MOSFETs. If I don't split my
supply (see earlier post) I'm thinking about making this type of
circuit this because the voltage drop in the MOSFET will be very small.

Size isn't an issue - suitable MOSFETs are in TO-220 type packages and
the LM358 is an 8 pin DIP package.


How much lower thatn 0.3V drop will the MOSFETs get you?

The forward resistance is around 0.015 ohms (HUF75337P3, 62A, 55V, TO220
package), so at 5amps that's a 75 mV drop. That looks like a worthwhile
improvement.

The MBR1035 was the lowest drop type (0.6v drop) I could find at RS
Components or Maplins, the only two decent retail outlets in the UK.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Lew Hartswick wrote:
Gary Emerson wrote:


With 18Amps of forward current capability (each), there isn't really
any "need" for the two diodes in parallel, but for an extra $5 and a
few extra minutes of wiring, if any one diode ever did fail "open" the
other would still provide power. Most likely overkill.

Yes because most often (probably at least 90% of the time) a diode
fails "short"
Therefore you may be reducing the reliability. :-)
...lew...

Fail "short" won't leave you without power on a flight. Fail "open"
might...