Unstable 12v power

**101RRS** · 8th April 2021, 11:17 AM

My 101 has a 24v system which powers start, lights, fuel pump and original instruments. I also have a 12v system that powers wasted spark ignition (EDIS 8 module), tacho, aftermarket instruments, engine low water alarm and digital voltage gauge. At this stage the 12v system is not charged by the vehicle charging system but later will be powered via a 24/12v Dc Dc charger.

A little while back I went to start the truck and didn't realise my smart charger was still attached to the 12v battery but it was also going through its battery rejuvenation/desulphurising program. My understanding is that it pulses current through the battery.

After starting the engine with the battery rejuvenation system on the electronic parts of the vehicle started playing up. With just ignition on there is no issue, but with the engine running the the 12v system seems unstable in that electronic displays flicker and jump around, the low water alarm sounds with a jittery sound and when I plug in a 12v meter into a 12v socket it just flashes - switch the engine off and all returns to normal.

I thought that maybe emf from the ignition system was jumping across the the 12v system as the main power line from the battery runs near the ignition so I moved the power line but no change.

So looking for suggestions before I start pulling things apart.

Thanks

Garry

**Homestar** · 8th April 2021, 01:20 PM

Assuming the earths are common between the 12 and 24 volt system? While it shouldn’t matter, I’m wondering if there is a condenser in the back of the 24 volt alternator that’s crapped itself and there’s some noise in the system? Shouldn’t make a difference but just a thought? Has the ignition system got anything in it that may cause issues like large capacitors, etc?

Do you have an old analogue multimeter at all? This will show fluctuations in the voltage far better than a digital meter unless you happen to have an occiloscope handy?

Just spitballing here mind you, it’s a bit of a strange one if it only started after the running of the engine with the charger connected.

**101RRS** · 9th April 2021, 12:01 AM

Thanks Gav - I have had similar thoughts. While the 24v charging light goes out i have not actually checked it is charging the batteries - now while it is separate to the 12v system there are a number of 24v relays that come on with the ignition and provide switched 12v to things like the engine watch dog - if the 24v system is not stable maybe it is crossing to the 12v system there.

I will break out the old multi meter and do some checking around.

Cheers

Garry

**Old Farang** · 9th April 2021, 02:35 PM

Not had anything to do with these hybrid type of systems, but I would be looking to check that the 24 volt generator is actually putting out DC, not AC or some where in between. Your charger MAY have damaged the 24 volt regulator.

**101RRS** · 9th April 2021, 04:49 PM

Good thoughts there - actually just checked the the alternator output and it is 28v DC. The charger was on the 12v system - charging the 12v battery so no direct cross over to the 24v system - only where a 24v relay acts as a switch to turn 12v systems on and off.

I am leaning to the HT system which is in the 12v system is causing the variations due to inadequate shielding somewhere.

Cheers

Garry

**AK83** · 10th April 2021, 09:05 AM

sounds like the charger caused a capacitor(or something) in the DC-DC convert to fail.

I'd be looking at the DC-DC first.

What charger did you use, ie. on the repair/desulphation mode on the 12v side?
My understanding of this mode is that it outputs quite a high voltage, at lowish current. about 16v at 1amp.
My NOCO does this, and from what I've read, C-Tek is similar(15.8v or whatever). And it's pulsed .. so maybe the pulse back to the DC-DC killed something within.

What do you have at hand to test with?
eg. do you have a 24v charger? if so, you could hook up a 24v charger to the 101 to charge it's batteries. Obviously 101 is not running. 24v charger should ouput about 28v or so and check if the 12v side is still flickering about.

If it all runs fine, then you know that it's something on the 24v side on the 101 that's causing the spikes/fluctuations.
Or, if it does the same thing as when the 101's 24v side is charging then more than likely the DC-DC has failed.

I would have thought that if the 101's 24v side is acting up, you would at least see some electrical device(light, gauge, or whatnot) also flicker or play up in a similar way too.
So why would it only direct an issue it has to the DC-DC converter to cause a flickering effect.

**101RRS** · 10th April 2021, 11:30 AM

Thanks Arthur but it does not have a DC to DC charger fitted at the moment - I charge the 12v battery at the moment via an old 240v SuperCheap smart charger. While the vehicle is driveable on the road it is a work in progress at the moment and a charged 100ah battery provides a lot of ignition pulses before needing recharging.

While I have a leaning towards unshielded ignition pulses crossing over into the other wiring but you could also be correct that the high voltage from the battery reconditioning process could have damaged the EDIS 8 ignition module or electronics elsewhere. Whan I took it for a run yeaterday, the ignition was running rough and the tacho would not go above 1200rpm - so maybe the tacho signal module is the culprit as it gets its input on the coil pack low tension input.

Cheers

Garry

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