any electonics engineers?

[wotayottie]

odd engine problem as posted earlier but things have moved on a bit now. After a sufficiently long run to get the engine well heat soaked I am getting the engine alarm buzzer sounding at idle every 22 seconds accompanied by a flicker from the alternator light. It all stops above idle and it never happens unless the engine has been run under load for maybe 2 hours.

Set up is a Volvo 2030 with a Sterling digi regulator and a solar panel with one of those regulators which cut it in and out several times a second rather than dump current through a resistor. The digi regulator is in the engine box and will get up to maybe 60/70C, but the engine panel is in the cockpit.

The volvo alarm is designed to sound continuously which suggests that the voltage problem that is likely triggering the alarm is itself only occurring every 22 sec. The regularity rules out vibration / broken wire. Incidentally, the voltage meter on the batteries is showing almost 14 v when the alarm sounds and the meter has been checked.

How does the alternator alarm work? The wiring diagram shows the connection being to D+ /61 on the alternator but it doesnt show what is within the black box that is connected to the alarm buzzer and the tell tale lights. I have been told that its a pcb of diodes and transistors rather than voltage sensitive relays.

But the real puzzle is the constant 22 secs ( counting 1001, 1002 etc) interval.

 

[alan]

Volvo Voltage Alarm

I had this problem with my Volvo after connecting solar panel(s). Although I did not have the regular 22 second alarm. In my case at tick-over revs sometimes the alternator alarm would sound, particularly when the batteries were fully charged. I put this down to the battery volts being higher than the alternator volts (which I understand is what the Volvo alarm circuit compares?); in my case I could "cure" it by increasing the revs untill the alternator was outputting a higher voltage.
Could the 22 second interval be something to do with your smart regulator cycle times??

Alan.

 

[wotayottie]

Not according to Sterling who make the digi regulator. And the odd thing is that the same set up worked without fault last year and with no alternations in the winter.

Is there any alternator fault that could cause the alternator voltage to drop temporarily every 20 secs or so? I cant think of one.

Incidentally, if I turn the engine off when I have the alarm sounding and then start it again just a few minutes later, the alarm has gone. So I cant see the issue being temperature breakdown of some circuit even though things in my engine box run hot.

 

[Evadne]

I had an intermittent "alarm flicker" at idle which went away when I changed the light bulb on the panel. I think the bulb is actually part of the detection circuit, and too high a resistance changes the low Voltage detection level, although I'm not speaking from a point of full and complete knowledge. But it's a cheap fix if it works.
I think if this happens it can give you a false indication if the charging current is too close to what is being drawn.

 

[Billjratt]

Usually the charge alarm and lamp are wired between the battery and the alternator field voltage. If there is a significant difference in either direction (battery too high as well as too low) the alarm may sound and the lamp may show a dull glow. I think the conditions you have now are : battery up to full voltage and alternator revving so slowly it dips enough to trip the alarm.
Last year your battery wasn't so fully charged maybe?
Also, when you've just used some battery power to start the engine, the 'fault' disappears, because the battery voltage has been brought below the critical level. You need to make sure the alternator/battery voltage is not too high, possibly the fault of the solar cells, try dissing them for a while.

 

[scottie]

Damp?

 

[wotayottie]

Usually the charge alarm and lamp are wired between the battery and the alternator field voltage. If there is a significant difference in either direction (battery too high as well as too low) the alarm may sound and the lamp may show a dull glow. I think the conditions you have now are : battery up to full voltage and alternator revving so slowly it dips enough to trip the alarm.
Last year your battery wasn't so fully charged maybe?
Also, when you've just used some battery power to start the engine, the 'fault' disappears, because the battery voltage has been brought below the critical level. You need to make sure the alternator/battery voltage is not too high, possibly the fault of the solar cells, try dissing them for a while.

I think I am finally beginning to understand how the system works but still not the problem. Today I wanted to be sure that the Sterling regulator was working so I set it for open lead acid batteries which meant that it raised the initial charging voltage at the battery to 14.8. The alternator output voltage was something just over 15v. This immediately cause the alarm to trigger albeit it a bit more often - maybe every 10 secs or so. And when the alarm triggered, the tacho flipped briefly to zero.

So the alternator output volts were well above the battery volts. Why did this trigger the alarm?

 

[savageseadog]

Not according to Sterling who make the digi regulator. And the odd thing is that the same set up worked without fault last year and with no alternations in the winter.

Is there any alternator fault that could cause the alternator voltage to drop temporarily every 20 secs or so? I cant think of one.

Incidentally, if I turn the engine off when I have the alarm sounding and then start it again just a few minutes later, the alarm has gone. So I cant see the issue being temperature breakdown of some circuit even though things in my engine box run hot.

First port of call should be Sterling who should know their kit and this setup very well.

I am an electronics engineer it could be many things but if you want to try yourself, I would test the battery(ies) before doing anything else, I would examine all the wiring and crimps very closely, that means undo and remove and put an ohmmeter on it. Look at the voltage that the Sterling is monitoring, preferably with a scope.

You just posted as I was writing this. I would suspect undersize wiring or corroded cabling.

 

[ianj99]

So the alternator output volts were well above the battery volts. Why did this trigger the alarm?

If the alarm takes its input from the alternator terminal (or starter solenoid if this is linked directly to the alternator) then it will see the higher voltage.

The alarm seems to be too sensitive - ie the voltage range where it doesn't rigger is quite narrow.
As for the delay, then this will be a feature of the alarm to prevent nuisance sounding due to voltage spikes. For example, a capacitor can be charged via a resistor, and the higher the input voltage the quicker the capacitor will charge upto the trigger voltage.

The circuit is most probably a 'window comparator' with the 'window' where the alarm does not sound being quite narrow. Delays using simple resistor/capacitor network will be used, as mentioned, to avoid nuisance triggering by filtering out noise and spikes.

 

[lw395]

Sounds like the voltage alarm is basically a pointless bit of junk you should get rid of.
You don't know what it's telling you.
You need alarms for temp and oil only.
Th voltage alarm could mask this.