Smartcom heavy duty unit clicking

[Ads1987]

Hi guys,

I have a 1.7 t25 diesel 1988 model, it's fitted with a zig unit and a smartcom "heavy duty" module, it doesn't seem to have another relay connected in the charging system, so by the looks of it and from what I have read on these forums;
The smartcom module measures the charge on both batteries and provided the main battery is charged enough it will then take power from it to charge the leisure battery?

when the vehicle is running the smartcom relay makes a constant audible click every second or so, it sounds like a relay is trying to switch but keeps flicking on and off.

Problem being I have wired my spot lights to the leisure battery and they actually pulse in brightness when the engine is running, I think this is because the battery is being charged, so does the smartcom relay charge in pulses?

The first solution is to wire the spots to the main battery, which I'm going to do anyway; but do you guys think this sounds ok or is that smartcom unit faulty?

Thanks for reading,

Adam.

[CJH]

Hi Adam

The smartcom relay measures the voltage at the main battery, and switches on and off according to two thresholds. The upper threshold, normally set to 13.5V, is high enough that it should indicate that the battery is being charged from the alternator, and this is the voltage at which the relay closes and connects the leisure battery into the circuit. When you turn off your engine and the alternator stops charging, the voltage in the main battery gradually drops back down, and when it reaches the lower threshold, normally set to 13.2V, it opens the relay to disconnect the leisure battery. When I installed my relay these thresholds were not set to anything like these values, and I had to tweak the thresholds using the adjuster screw inside the unit, next to the permanent live and earth connections. I did this by trial and error, using a voltmeter across the main battery and starting and stopping the engine until the relay triggered at the right times.

What I did find was that when I start the engine the voltage rises quite quickly to the upper threshold so that the relay closes, but as soon as it closes, the leisure battery (if not up to the same voltage as the main battery) will drag the measured voltage down a bit. In my case it didn't take it low enough that the lower 'relay open' threshold was reached, but I can imagine this might be happening in your case, due to the spotlights. I think what might be happening is the following:

1) You turn the engine on - the alternator starts charging the main battery
2) The upper 'relay closed' threshold is reached, so the leisure battery is connected in - at this point your spotlights will be bright because they're seeing the alternator charge.
3) The drain on the leisure battery (due to the spotlights), and perhaps its general condition, are such that the apparent voltage of the two batteries combined is below the 'relay open' threshold, so the relay opens and disconnects the leisure battery - your spotlights will now dim because they are only connected to the lower voltage of the leisure battery.
4) Separated from this load, the voltage across the main battery will now rise again, so the relay closes again, and this will now go on ad infinitum.

If this theory is correct, the solution will be to run the spotlights from the main battery, as you suggest.

Chris

E D I T: If this relay cycling is happening even when the spotlights aren't on, then maybe your leisure battery has a low voltage and/or is on it's way out, so that any time it connects to the main battery it drags the combined voltage down. Do you have a meter to check the voltage on both batteries?

[California Dreamin]

Sounds plausible, especially the suspect leisure battery comment. I would also add an and/or....concerning the voltage regulator....disconnect the leisure battery temporarily and check the charge rate off idle (say 2K). You should be seeing 13.9 - 14.2 volts (unloaded) across the starter battery terminals (original Beru/Bosch regulator brush pack) possibly as high as 14.5 volts with an aftermarket pack fitted.
I suspect your reading to be much lower (13 - 13.5 volts) which is too little and is too close to the Smartcom's switching threshold.

Martin

[CJH]

Sounds plausible, especially the suspect leisure battery comment. I would also add an and/or....concerning the voltage regulator....disconnect the leisure battery temporarily and check the charge rate off idle (say 2K). You should be seeing 13.9 - 14.2 volts (unloaded) across the starter battery terminals (original Beru/Bosch regulator brush pack) possibly as high as 14.5 volts with an aftermarket pack fitted.
I suspect your reading to be much lower (13 - 13.5 volts) which is too little and is too close to the Smartcom's switching threshold.

Martin

Hi Martin - my own alternator was only getting up to about 13.2V, so I followed the advice given to me in another thread and fitted a new regulator. It's raised my charging voltage a bit, but it's still only around 13.5V I think. Would this be a sign that there's something else wrong with my alternator perhaps, or maybe my main battery is past it's best?

Anyway, I've been able to tweak my smartcom relay to work with lower thresholds, and it seems reliable enough. I hadn't previously thought of the scenario I described above, but to add to the other issues with the smartcom (threshold setting, taking time for the relay to close, relay remaining closed for some minutes after the engine's switched off) it seems like a failing leisure battery could conceivably create this on/off behaviour. All in all, I'm hard pressed to see a killer advantage to the smartcom, and would be happier I think with just a conventional relay setup.

[Ads1987]

Ok thanks guys, the relay clicks whether the spots are on or not so I think by the sounds of it the first thing to check would be the condition of the leisure battery.

Ill get a meter and measure what you suggested and then have a look into tweaking the thresholds.

[California Dreamin]

I'm not a fan of the SMART relay TBH for the above reasons....replying to CJH I would say that after the new regulator brush pack you really should be seeing 14+ volts, so something is definitely not right.
Have you measured output directly at the alternator? sounds like substantial voltage drop...as I said, take the leisure battery out the equation by disconnecting it and record the difference in output between what's at the starter battery and that found directly at the alternator.

Martin

[CJH]

I'm not a fan of the SMART relay TBH for the above reasons....replying to CJH I would say that after the new regulator brush pack you really should be seeing 14+ volts, so something is definitely not right.
Have you measured output directly at the alternator? sounds like substantial voltage drop...as I said, take the leisure battery out the equation by disconnecting it and record the difference in output between what's at the battery and that found directly at the alternator.

Martin

Hi Martin - Thanks, I looked into doing that, but measuring the output at the alternator isn't easy because the terminals are fairly well protected so it's not easy to get to bare metal, especially given the position of these terminals. For the voltage at the battery terminals to be significantly different to the voltage at the alternator the resistance in the alternator cable route would have to be very high wouldn't it? I guess that's a worry in itself, so maybe I should persevere with a direct measurement.

[California Dreamin]

As you say but not as difficult as it might seem, just be careful not to short anything in the process.
Don't rule out poor earths to the body...at the battery, to the gearbox and in the engine bay. Remember that you don't necessarily have to clean an existing main earth as a completely new one can be added as a belt and braces approach.

Martin

[bigherb]

Thanks, I looked into doing that, but measuring the output at the alternator isn't easy because the terminals are fairly well protected so it's not easy to get to bare metal, especially given the position of these terminals.

You can check the alternator voltage easily there is a spare terminal for a suppressor marked with a + next the the main terminals, just make a small fly lead to connect a meter to it.

[ghost123uk]

The folk I camped with last weekend had exactly this and Chris's diagnosis was the cause, a knackered leisure battery dragging the whole system down below the relay threshold voltage = click click click click

p.s. Whilst on the subject, protect your leisure batteries from harmful over discharging by fitting one of these = "LVDs" I use this one HERE

[CJH]

You can check the alternator voltage easily there is a spare terminal for a suppressor marked with a + next the the main terminals, just make a small fly lead to connect a meter to it.

Brilliant, thanks! That's another job for this evening then.

[ghost123uk]

Note what bigherb says about making a fly-lead up (Lucar connector on a bit of wire) because it is all too easy to get a meter probe to short against the body of the alternator, when attempting to touch that terminal. And you don't want to do that !!!!

[CJH]

Note what bigherb says about making a fly-lead up (Lucar connector on a bit of wire) because it is all too easy to get a meter probe to short against the body of the alternator, when attempting to touch that terminal. And you don't want to do that !!!!

Noted, thanks!

[California Dreamin]

even easier if you have a later 65amp or 90ah alternator with 8mm post.

As I said earlier.....it is important to disconnect the leisure battery whilst doing this to eliminate any affect it might be having BUT in the process of DIAGNOSIS, it might be worth reconnecting and comparing the difference 'With' & 'Without' this second battery connected.

My money is on a 14+ volt output once the leisure is disconnected BUT the difference between what you see at the alternator and across the starter battery still remains of interest...this should be minimal (certainly less than 0.3 volts). engine running, no load, say 2,000rpm

Martin

[CJH]

Hi Martin
On reflection it could well be the leisure battery causing the drop in voltage. Before I fitted the new regulator I checked with the smart relay fuse removed, so that I could rely on the leisure battery staying disconnected. But I must admit I haven't done that since fitting the new regulator, so there's an outside chance that my voltage check after fitting the regulator was corrupted by the leisure battery. In fact it must have been, since the smartcom relay closes when the voltage hits the threshold, which therefore means it will have connected before the main battery voltage reaches its maximum. D'oh - I'll be sure to check methodically this evening.

Thanks for your suggestions.
Chris