Contactor economizer

[manny]

Have seen a couple of different solutions to make a contactor coil economizer. The simplest one is the resistor and capacitor in line. For my contactors the resistors will dissipate 6.5W so they need to be big.

On the forum I have see someone using a resistor and capacitor in combination with a dcdc converter to supply the hold current. In this case the resistor is there mainly to discharge the capacitor after switch off ready for the next use.

I have taken this idea a step further. Use a dcdc converter and at switch on bypass it with a mosfet. The dcdc converter is a mini360 really cheap

With the first prototype I built up there whas a problem, the dcdc converter got quite hot. After some troubleshooting I put the scope on the switch node on the dcdc converter. It whas not stable at all, random pulse timing and pulse length. The datasheet suggests an extra compensation capacitor (C6) so I guessed that 10nf would be in the right range. And it workt, nicely spaced pulses

before

after

This is the resulting voltage on the coil.

I have several contactors from volvo V60 hybrid packs.
They are made by Tyco Electronics. the pack has two types:
- 2138084-1 EVC 500 Main Contactor 450VDC 500A coil 3.14Ω
- 2138084-1 EVC 135 Contactor 450VDC 135A coil 3.8Ω

The datasheet states: "Un-economized coil must be economized by the customer to avoid overheating"

For the EVC 500 the datasheet gives a minimum hold current @ 650mA
For the EVC 135 the datasheet gives a minimum hold voltage @ 2V

[Zieg]

Pete made a pretty nice one with a DRV103 a while back, have been using it during all the tests on my build and so far so good. viewtopic.php?t=3636

[andybpowell]

I see what you have done but didn't feel the need for additional complication when I did it just an additional resistor and capacitor in series placed in parallel around resistor 2 in the diagram provided a 12v peak on power up to pull the contactors in and then drops to hold voltage why over complicate it ?