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
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.png)
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
![Smile :)](./images/smilies/icon_e_smile.png)
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