240VAC power relay coil diodes

[SparkyTris]

trying to fix a dysfunctional booster-starter-charger. there is a large chinese relay (part nr WJQX-38F-2H) which has a funny little set of diodes which seem to ahve been connected across the coil terminals.
I would have expected a diode in this position on a DC coil but Im not sure what the idea is on an AC coil....
anyway the diode board has clearly been toasted, and resultant arcing seems to have blown off the coil conductors resulting in open circuit.
I have attempted to trace out the nasty little PCB carrying the diodes and .... weird. I cannot work out what it's supposed to do. the diodes are marked A7
maybe they are not even diodes?
very low quality chinese parts by the look of.

relay body is marked "FOR-YOU-R-OW-N-SAFE-TY" which is encouraging.

 

[ericmark]

I would guess a DC relay to stop any chatter, and a full wave rectifier. However battery chargers today are complex little things, often including some switch mode technology and often only way to repair if repair is the right word, is to replace circuit boards.

 

[bernardgreen]

The diodes on an AC coil would normally be back to back Zener diodes rated at 400 Volts ( for a 230 V coil )

 

[SparkyTris]

yeah I wondered if they were zeners. 2 diodes checked out OK 0.5V forward & open cct revers. the other 2 were dead short.
replaced them with 1N3094's tried it. relay chattered away like it didnt have enough pull.
coil meters at 5K.
think the coil must have gone o/c.
replaced it with a contactor, seems to be working now.
it is a Maypole charge/starter. no intelligence whatever just a whopper trafo and rectifier.

interestingly it comes retail boxed with an unterminated 2.5mm mains tail, instructions specify that it will blow fuses if conencted to a 13A plug, and that it should be connected to a 32A supply via industrial plug.
not too familiar with legislation but this *feels* like it might be on the dodgy side. weird for Maypole, they are a popular & recognised brand.

 

[SparkyTris]

I would guess a DC relay to stop any chatter, and a full wave rectifier. However battery chargers today are complex little things, often including some switch mode technology and often only way to repair if repair is the right word, is to replace circuit boards.

I wondered that too but on close inspection, the relay's coil inside was tape-wrapped and on the tape was stamped 240VAC.

 

[SparkyTris]

by the way the relay's sole function is to jumper the trafo in some simple way that I didnt bother to follow for the cranking amps function