12v socket low voltage

[jw4821]

I’ve got a small 300w inverter in the back of my van, connected to the 12v socket in the back.  

It’s recently started beeping/alarming even with the engine running. After further investigation with a multimeter, with the engine at idle the 12v supply is dropping down to around 11 volts, and then back up to about 13-14v. 

This only happens after startup and it does this a few time before settling down. 

Anyone know why this might be? Annoyingly when the inverter sees this it cuts out and doesn’t provide power until it’s completely power cycled.

[shtu]

Not specifically, but I'd start by checking the voltage at a few other places at the same time. May b a general system problem rather than just that socket, and it's just the inverter is sensitive to it.

I recently drove mine 50ish miles with a duff alternator, and the low battery light only came on ocassionally. The battery warning light is not immediate on the alternator failing.

Mine had a habit of providing 14-15v, then failing once driven above idle. Turned out to be the slip rings, and that condemned the alternator.

[Drummond]

the engine at idle the 12v supply is dropping down to around 11 volts, and then back up to about 13-14v. 

This only happens after startup and it does this a few time before settling down. 

The alternator starts charging only after about 4 seconds after the engine has fired. During this time, voltage may well be below 12V, maybe at 11.7V or even less, depending on consumption. Once it jumps active, it should not fluctuate anymore.
Separate strategy then is the ”micro-hybridy” of the e-Hdi. I’ve seen alternator resting at 12.4V at lowest on cruise, given the battery management thinks the battery has enough charge.
If your issues have started only recently, then it ofc would indicate something is not right anymore.

[jw4821]

the engine at idle the 12v supply is dropping down to around 11 volts, and then back up to about 13-14v. 

This only happens after startup and it does this a few time before settling down. 

The alternator starts charging only after about 4 seconds after the engine has fired. During this time, voltage may well be below 12V, maybe at 11.7V or even less, depending on consumption. Once it jumps active, it should not fluctuate anymore.
Separate strategy then is the ”micro-hybridy” of the e-Hdi. I’ve seen alternator resting at 12.4V at lowest on cruise, given the battery management thinks the battery has enough charge.
If your issues have started only recently, then it ofc would indicate something is not right anymore.

I think this is the crux of the issue. I've recorded the multimeter screen and you can see the volts bomb down during engine start and then gradually ramp up to 14v. 

Probably doesn't help that I also tend to turn the ignition on and leave for a few seconds before starting, so the voltage drop is even more pronounced to the inverter.

This video was taken about an hour after than van had been ran so I suspect the first start on a morning is worse than this

Video

Only solution I can think of is some sort of 12v delay timer/relay. Anyone know what the fuse rating is of the 12v socket in the load area, so I can specify the correct sized relay?

[shtu]

This says 30 amp, though that is for both,

https://fuse-box.info/citroen/citroen-be...2018-fuses


I know it's a bit of a bodge, but how about a simple switch in line with the warning sounder of the inverter?

edit - would this do what yo uwant? https://www.delcity.net/store/Time-Delay...5.h_804416

[Mark604]

Looking at your video am I the only one who sees nothing wrong?
Your initial voltage steadies at 12.3 then after starting goes up to 14.07.
Why does your multimeter reset at the beginning?

You say, "....with the engine at idle the 12v supply is dropping down to around 11 volts, and then back up to about 13-14v. "
So what does it do when not at idle? Say a couple of hundred revs above?

I admit my knowledge is probably lacking and out of date, but I seem to remember from years ago something about having to go initially a little above tickover after start up to get the alternator charging properly. But so then on modern cars you will get the full charge rate from the alternator when never above tickover?

[Drummond]

I agree, on the video above the voltage ramp up looks normal.

Below is my log capture of starting e-hdi with worn battery. X-axis is time in seconds.

Initially, voltage is maybe 12.4V.

1. At 4.0 seconds key is turned on but not cranking yet. Some fuel pump action or such preparation can be seen for couple of seconds.

2. At 10.0 seconds the key is turned to cranking. You can see deep momentary dip, and then the boost from the ultra capacitor as the startstop is aiding the cold start.

3. At about 10.5 seconds the engine has fired. Electrics are running on battery, voltage below 12.0V.

4. At about 13 seconds the alternator starts ramping up the charging, and as we can see, full charging is going on at 14 seconds, i.e. only 3-4 seconds after the engine has fired.

[jw4821]

Me again....it's still not right sadly.

I've purchased a delay timer relay which I've set to 2 mins. So engine on, relay opens, 2 mins later (when the voltage should have certainly stabilsed!) it closes and the inverter has power.

This works fine, however it's still alarming for low volts and when checking with a multimeter the voltage is indeed briefly dipping to 10-11v. It's sporadic and random, and the dip happens even when on the motorway with the engine at 2-2.5k rpm.

The only thing I can think of is something electrical that is very power hungry is engaging (AC compressor?) causing the brief dip.

Not sure where to go from here other than:

- A feed directly from the battery, which with the engine running is a solid and stable 14 volts. But this involves messing around with cables probably routed underneath the van

- Installing a small 12v battery somewhere between the 12v socket and inverter to act as a buffer. I've not really got the space for this though.

[jw4821]

Any mileage in changing the main battery under the bonnet? 

It's a 68 plate van and on the original battery so approaching 6 years old.

[jw4821]

For those interested I''ve finally gotten to the bottom of this....it's actually the Makita battery charger!

Hooked up a 12v battery to the inverter and it behaved very similar to when connected to the van (i.e voltage drops and inverter cutting out).

I then plugged a mains 240v sander into the inverter and everything was perfect. Connected back to the van and plugged in a few more appliances - absolutely fine. Plugged the battery charger back in, chaos resumed!

The sole purpose of the inverter was to charge batteries for tools, so not sure how I'll get around this. But at least I know the van and inverter are fine!

Thanks again to everyone who suggested things along the way.