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G'day All

Being cheap, poor and.. well, "thrifty", I have to make the most of
what I've got. So here is one of the things I've done, and brings up
a topic of sharing thrifty tips in an EV context.

Using surplus (not Ebay, but similar) contactors with 48V coils and
72V coils, instead of (more expensive) 12V coil ones. Also using DC
input power supplies with multiple output modules (Lambda Omega
units) that do duty for 120V to 12V system DC/DC and also provide the
voltages for the 48V and 72V coils (thanks Richard, if you're watching!).

But having a pair of 48V coil contactors to turn on the DC converters
that give me 48V is a little catch-22.

Fortunately these contactors turn on at about 31 volts, and will
actually hold in quite well with only 12 volts.

So a 3-pole relay, 2 x 10,000uF capacitors, 2 x 100-ohm resistors and
3 x diodes makes a simple 'pump' circuit, that charges up the two
10,000uF capacitors, then when the relay switches puts them in series
with the 12V supply to give a solid 36 volt pulse to pull the
contactors in. All from my collection, nothing in this circuit bought
specifically for this job.

Ascii art time:

+12V from battery
|
-|-|>|----------
| D1 |
| |
| o- |
|-|>|- o\ |
| D2 | \ |
| / \-----
| R1\ |
| / o--------)--> out
| \ | to
| | ------ === coils
| | | | C1|
| | / o----| |
| |R2\ o\ |
| | / \ |
| | \ \-----|
| | |
| | | o--------
| --)-------| |
| | |
| | |
| |------- ===
| | o-----|C2|
| | o\ |
| | \ |
| | \-----|
| |
| | o----|
|-|>|----)------|
D3 |
|
ground (neg)

For clarity I've omitted the control coil, but it would work equally
as well with a 3-pole switch.

It takes about 10 seconds to recharge the capacitors for the next go,
would be quicker with lower value caps and/or resistors, but I wanted
a solid pulse, and to use 0.6W resistors for low-mass mounting
(straight in the wires at the relay). If a capacitor fails short, the
dissapation will be 1.4 watts, and should blow the resistor open
without a fire.

I bought recently for $14 including postage a "DC Power Supply 10~32V
to 12~35V 100W Converter Module" from Ebay that could have been used
to power the contactor coils, too. (using the search term "DC Power
Supply 100W Converter" gets more hits).

Regards

[Technik] James

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