Relay dropping out momentarily

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Originally Posted by newkirk

Can't we surmount this with a capacitor on the output?

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Well I've been consulting with a friend/coworker on this. (he regularly disassembles, debugs, and rebuilds SMT circuit boards - I have only moderate knowledge in that area, I'm in the software and communication end of things) His first suggestion at amelioration was to drop a diode across the relay. Unfortunately, while that led to a noticeable improvement at first, it still drops out. (just not as noisily)

Round 2 probably tomorrow, will report back what transpires. Gonna see if he can propose a root cause as well as an effective fix. (and eventually we'll get around to ordering a replacement voltage regulator so I can fix my Brain:rolleyes:)

j

First we tried with a 1000v 2.5a diode across the relay. (the cathode (white-banded) end is connected to the positive (red wire) terminal on the relay) Helped some but it still dropped out. It drops out less frequently at first, but the most noticeable change is that most of the buzz/hum is gone.

Then we added a ~0.6µf capacitor, made minimal difference.

Finally I've got the diode together with a 10µf capacitor (neg to neg if it's polarized) and it stays on. :nod:

(we're still going to try to find the cause next week, though)

j

any word on the cause yet? I'll try the diode and capacitor.

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Originally Posted by acbusdriver

any word on the cause yet? I'll try the diode and capacitor.

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Unfortunately no, we didn't have a chance this week. Sadly, the friend+coworker helping me with this is fighting his second battle with lung cancer, and isn't always at work, or working at his best.

j

I'm having the same problem on all 4 off my brains in the car. Some relays are buzzing rather loudly, which is a real problem considering there are over 30 relays, and some are just dropping in and out randomly. I'm going to check mine to see if it's the one's on the 2 ends as well.

Hope someone finds a solution for this, buzzing and clicking relays are not a good thing in a show car!

I think the problem is actually simple... the board wasn't made to support enough current to the outputs. The resistance is too high and there is too much of a voltage drop. The drop only increases with more current passing through, more relays, more drop.

This is actually an issue for me now again. Though this brain is perfectly working, and though 11 volts is enough to push a relay, the voltage drop to under 10 volts the brain causes is an issue.

In all honesty, nearly all of my reliability issues in the car are due to the Fusion Brain. I'm swapping it out for an arduino soon.

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Originally Posted by PaulF

I think the problem is actually simple... the board wasn't made to support enough current to the outputs. The resistance is too high and there is too much of a voltage drop. The drop only increases with more current passing through, more relays, more drop.

This is actually an issue for me now again. Though this brain is perfectly working, and though 11 volts is enough to push a relay, the voltage drop to under 10 volts the brain causes is an issue.

In all honesty, nearly all of my reliability issues in the car are due to the Fusion Brain. I'm swapping it out for an arduino soon.

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I don't think that's the problem. I have this problem regardless of the number of relays i'm running, and the frequency of the dropout on any given output doesn't increase with more relays. In fact, the dropout still happens just as frequently on the outputs with nothing attached to the brain. I can see the LEDs on the output flicker every time there's an interruption.

I'm running a full 12 volts on mine and most of my tests of this problem have been with only one relay attached to the brain. So it's not a low voltage issue. With one relay, yes it takes a bit of current to pull the relay closed, but once it's closed, a relay draws very low current.

That said, the voltage across the outputs on my brain, even with 12V attached, ranges from 10 to 12V, but I was able to close the relay on 9V (it didn't do it happily, buzzed real loud and took a second, but it did close) and holding current is very low so the dropout doesn't seem to be related to the voltage.

Hmm... my problem only happens with the relays connected and does increase with the number of relays connected. Certain output are worse than others. For example, if my battery is at 11.0 volts and I try to turn on the relay on output 8, it's not possible. If the voltage is up around 11.5, it does it just fine.

If I look at the output with a multimeter, it can be as low as 8.6 volts. There's definitely some ridiculous resistance going on there.

newkirk... what is the purpose of the diode across the coil? I could only see it as a way to prevent the induced current from flowing back to the brain when the power cuts, but I don't understand how that would keep the relay from dropping. I am going to try adding a capacitor, and if you can explain to me why I'd use a diode (since we are dealing with DC already), I might try that as well.

You shouldn't need a diode across the coil - that's for back EMF, and the drivers we use on the brain are back-EMF protected.

You shouldnt need a capacitor, either.

Email us for replacements - fusioncontrolcentre@gmail

EDIT: Turns out we've replaced both of yalls, and the ones you sent back worked fine.

What are you using to power the board? Have you verified its output voltage with a DMM?