Battery Vehicle Society

Hi All,

Update: been driving around the last few days pulling a main fuse then disconnecting the LV battery whenever I was parking for more than an hour or so.

Found the time today to go through the options, test the battery properly, start taking bits off to check things like the relay and the temp sensor.

Just needed to run one errand first. Reconnected the LV battery, fan came on. Re-inserted the main fuse, fan went off. Fan stayed off. Fan is /still/ off. I've been outside several times to check it hasn't turned itself on. It hasn't yet.

So for the moment I'm holdng my breath. I'll run a proper battery test when it stops raining (I'm in Wales) and try to add to my knowledge by working out where the potentially problematic bits actually are. If it re-occurs or if I find out more I'll update the thread so it's here for the next person with a sticky fan.

Until then can I just thank everyone for the help and support? It was much appreciated and I hope I'll get the chance to buy you a drink at some point.

Cheers,

Evan

Hi,

For completeness, another (hopefully final) update.

After the marathon 'fan on' stuff in May the fault didn't go away but did reduce in frequency. About once a week the fan would stick on, I'd pull a fuse and disconnect the LV battery on parking it up and usually after two or three such 'resets', or after charging, the fan would go off and behave normally for a few days.

Seperately, I'd always had a minor issue with getting the van to 'start'. Sometimes, about every third start, I'd turn the key and no clunk. If I paused it would usually start second or third go. Occasionally more often. More likely first thing in the morning. Anyway, the other day I wasn't paying attention, turned the key and 'drove' downhill out of my drive to coast to a gentle stop in the road, where I realised the engine wasn't on. After much swearing and no starting (it did eventually) I resolved to change the LV battery as the old one seemed marginal.

Bought a new battery - and the fan hasn't played up since. It hasn't /entirely/ cured the occasional no-start problem which still happens occasionally but at least I don't have to get the bonnet up and pull fuses every time I park up. So the regular advice of "if it does wierd things change the LV battery" seems to hold good for this one.

Cheers,

Evan (J)

Glad its sort of fixed it.

The 12v does seem to play a major part of keeping the electronics happy.

The odd starting could be down to a dodgy ign switch possible ??

ChrisB

The hesitation to click the contactor could be down to the new battery not being fully charged. If its above a certain voltage the DC to DC wont cut in to charge when the vehicle is turned off, but it may be high enough to do what you need, just not enough to do all you need when starting . Check the battery voltage, while its standing and when its running, I may improve as you use it and charge up the battery to its full extent. The DC to DC provides a large proportion of the running current. If you have lights heater , power steering under usage etc the battery wont be getting topped up to its max but using up power. You could try giving it a bit of a help by giving the new battery a decent charge.

Grumpy-b

Grumpy-b wrote:The hesitation to click the contactor could be down to the new battery not being fully charged. If its above a certain voltage the DC to DC wont cut in to charge when the vehicle is turned off, but it may be high enough to do what you need, just not enough to do all you need when starting .

Well, your mileage may vary but I think that will not be the problem.

The DC to DC provides a large proportion of the running current. If you have lights heater , power steering under usage etc the battery wont be getting topped up to its max but using up power. You could try giving it a bit of a help by giving the new battery a decent charge.

That's not quite right, the DC-DC provides *all* of the 12V current that the vehicle can use.

Grumpy-b wrote:The hesitation to click the contactor could be down to the new battery not being fully charged. If its above a certain voltage the DC to DC wont cut in to charge when the vehicle is turned off, but it may be high enough to do what you need, just not enough to do all you need when starting .

Well, your mileage may vary but I think that will not be the problem.

The DC to DC provides a large proportion of the running current. If you have lights heater , power steering under usage etc the battery wont be getting topped up to its max but using up power. You could try giving it a bit of a help by giving the new battery a decent charge.

That's not quite right, the DC-DC provides *all* of the 12V current that the vehicle can use, apart from very short-term spikes from e.g. the wiper motor or electric windows.

The Dc to DC does provide all the power as it has to change the traction power to 12v. But the 12v battery does give a buffer that must allow a peak current to be delivered in excess of the DC to DC convertor. That is supported by the fact that many DC to DC units have been damaged when the 12v battery goes.
Grumpy-b

Grumpy-b wrote:That is supported by the fact that many DC to DC units have been damaged when the 12v battery goes.
Grumpy-b

Ah .........my take on the DC-DC going west when either the 12v bat dies or if you remove the 12v BEFORE isolating the main pack was due to the converter using the 12v to reference its output and thus sort of goes into a run away situation

ChrisB

ChrisB wrote:

Grumpy-b wrote:That is supported by the fact that many DC to DC units have been damaged when the 12v battery goes.
Grumpy-b

Ah .........my take on the DC-DC going west when either the 12v bat dies or if you remove the 12v BEFORE isolating the main pack was due to the converter using the 12v to reference its output and thus sort of goes into a run away situation

ChrisB

No,

Grumpy-B wrote:the 12v battery does give a buffer that must allow a peak current to be delivered in excess of the DC to DC convertor.

This is correct (also what I said). But that peak current only exists for milliseconds, on average it is charging the battery.

What I was arguing with was the idea that the 12V battery wouldn't be getting fully charged if you started out with it not fully charged? Perhaps that's not quite what Grumpy-B was saying, so I was just trying to clarify.

All that is needed is a battery that is healthy - a new battery one one which tests OK on one of those cheap resistor testers will be perfectly fine, even if it's a bit flat. Batteries that have been allowed to sit dead flat a few times are the problem (as they have such high internal resistance that they may as well not be there).

EVan wrote:

ChrisB wrote:

Grumpy-b wrote:That is supported by the fact that many DC to DC units have been damaged when the 12v battery goes.
Grumpy-b

Ah .........my take on the DC-DC going west when either the 12v bat dies or if you remove the 12v BEFORE isolating the main pack was due to the converter using the 12v to reference its output and thus sort of goes into a run away situation

ChrisB

No,

Ah interesting .........

EVan wrote:

Grumpy-B wrote:the 12v battery does give a buffer that must allow a peak current to be delivered in excess of the DC to DC convertor.

This is correct (also what I said). But that peak current only exists for milliseconds, on average it is charging the battery.

What I was arguing with was the idea that the 12V battery wouldn't be getting fully charged if you started out with it not fully charged? Perhaps that's not quite what Grumpy-B was saying, so I was just trying to clarify.

All that is needed is a battery that is healthy - a new battery one one which tests OK on one of those cheap resistor testers will be perfectly fine, even if it's a bit flat. Batteries that have been allowed to sit dead flat a few times are the problem (as they have such high internal resistance that they may as well not be there).

So whats killing the DC-DC then, is it the millisecond spikes that causes them to fail if the 12v isnt good or even connected ??

ChrisB