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Relay chatter problem

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thorntonforce

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I have been doing installation work on a vehicle and have encountered a problem. I have 2 AC electrical inputs to the system, a 1kw inverter and a socket for external mains electricity or generator. When the inverter switches on it powers the coil of an ac relay which switches the contacts from normally closed (external socket) to normally open (also the inverter). the common contacts of the relay connect to the input of my consumer unit. Downstream I have multiple sockets and lights etc.

the system works fine and switches seamlessly between the 2 inputs with no loss of power to my PCs and monitors etc. Unfortunately I cant run the fluorescent arc lighting I have installed from the inverter. There is plenty of capacity to run them but the initial inrush current causes a voltage drop on the inverter which switches off the relay. the result is high frequency relay chatter and the lights never come on.

If this was a DC voltage drop problem I would consider using a large capacitor but this wont work for AC - will it??

Is there any other solution??

Thanks in advance
Nick
 
If this was a DC voltage drop problem I would consider using a large capacitor but this wont work for AC - will it??

Probably not. I've had more problems with AC relay chatter than DC. They effectively cut out twice each cycle anyway, and it's only the sheer momentum of the armature that keeps the circuit from being broken even when the sorry things are working properly.

However, if the problem is actually high-frequency noise from that arc lighting you mentioned, then a cap might do the job and help smooth out the noise in the line for everything else attached, too.

Say you used a .22μf poly cap (don't use ceramic) rated for a good 250V. This would present a 13kΩ impedance @ 60Hz - too much resistance to affect anything. At 20kHz, however, it would only present 36Ω, and short a lot of HF noise to ground.
 
I have virtually the same system. Better quality ballasts have a lower THD ( Motorola typically 5%) I believe there is a good chance this will cure the problem.
 
The OP is thinking it's an inrush current prob. He'd need a decent inductor sitting just before each ballast to limit that. The inductor will also inhibit HF noise via by converting the HF to heat energy. A cheaper alternative is a -ve coeff thermistor. This works well if power isn't cycled off and on frequently as the thermistor needs a cool off period of a few minutes w/o forced cooling.
 
In my system the relay (ATS) coil is energized by the DC battery voltage so I don't get problems.
The coil is fed thru an Under Voltage relay with adjustable time delay.
 
The OP is thinking it's an inrush current prob. He'd need a decent inductor sitting just before each ballast to limit that.

An inductor will limit inrush current with DC, but with AC it will only present a fixed reactance to the frequency.

Your NTC thermistor idea might do the trick. The ballasts probably already have one if they are electronic, but adding a bigger one externally may be a cheap and easy fix.
 
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