I use many 40 amp 1" cube automotive relays with 12 VDC coils. The 
sockets are available with the diodes installed.

On 3/17/2010 8:25 AM, Peter Feucht wrote:
> Hi,
>
> For me it sounds like missing spike suppressor diodes.
>
> As long as several relays are activated the spikes, which are generated by
> swiching off another coil will be suppressed by still activated relay coils.
> But when you switch off the last relay there is nothing left which would be
> able to supress the spikes...
>
> Just add a common diode (1N4148 will do) across each relay coils.
>
> Regards
>
> Peter
>
> Hi people
> I have a circuit where I have a pic16f877 that commands four water pumps.
> The connections between the pic and the pumps is made this way:
> PIC ->  5k6 resistor ->  Bc337 transistor ->  relay ->  contactor ->  pump I
> start the pumps in secuence and when a presure sensor signals, I shut down
> every pump one by one.
> When the last pump stops, the pic resets, and it should not.
> Could it be my interface pic-pump the problem?
> Could it be some EMI interference from contactors or pumps resetting the
> pic?
> The most strange thing is that it resets only when the last pump power off.
> the software is ok, because I put the circuit in my workbench, with leds
> simulating the pumps and it works great.
> If somebody has a clue, let me know.
> Thanks a lot!
> Matias
>
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> Matias Vidoni
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