Battery voltage dropping low with full electrical load

**unity** · 15-06-2009 10:43 PM

I've noticed that my battery voltage is dropping below 12V with a full electrical load while in idle. Is this normal?

**tron07** · 16-06-2009 08:53 AM

where does this device take the reading from?

**aaronng** · 16-06-2009 09:27 AM

If your revs are low, then you are not producing as much juice from the alternator, hence the battery having to bear the brunt of the current draw and the voltage will drop slightly.

**unity** · 16-06-2009 10:25 AM

Originally Posted by aaronng

If your revs are low, then you are not producing as much juice from the alternator, hence the battery having to bear the brunt of the current draw and the voltage will drop slightly.

I think the reading is taken from the ECU.

I thought taking the battery voltage under certain conditions was a way of testing your battery/alternator. I haven't found information on the Euro but I've found information on other cars and the numbers seem very similar.

Voltage with car off approx 12V. Mine 12.1

Voltage with car on at idle, no electric load 14V. Mine 14.1

Voltage at idle with full electric load not less than 12V otherwise could be battery/alternator problem. Mine did show a reading as low as 11.6V

**integral90** · 16-06-2009 11:09 AM

Your coolant might need a top up

**unity** · 16-06-2009 12:19 PM

Originally Posted by integral90

Your coolant might need a top up

I checked my coolant and it's at the maximum level. My last service was only 3 months ago.

I have noticed starting my car on a cold night (with electrical load) that the idle suffers (louder(whine?) and rougher) so I was told that my alternator might be struggling with the load.

Is there any other test I can do or any other sensor I can monitor that will give a more definite answer?

**integral90** · 16-06-2009 12:45 PM

Originally Posted by unity

I checked my coolant and it's at the maximum level. My last service was only 3 months ago.

I have noticed starting my car on a cold night (with electrical load) that the idle suffers (louder(whine?) and rougher) so I was told that my alternator might be struggling with the load.

Is there any other test I can do or any other sensor I can monitor that will give a more definite answer?

Haha, I didn't mean that the coolant would be affecting volatage, just that I always try and stop my coolant reaching 90 or above.

You can just start the car with the radio, lights, seat warmers etc. off until the idle starts to drop a bit. That's what I do and I don't get any of the whine you're talking about.

**unity** · 16-06-2009 01:58 PM

Originally Posted by integral90

Haha, I didn't mean that the coolant would be affecting volatage, just that I always try and stop my coolant reaching 90 or above.

You can just start the car with the radio, lights, seat warmers etc. off until the idle starts to drop a bit. That's what I do and I don't get any of the whine you're talking about.

How do you manage to keep your coolant under 90? Mine was noted at 90 in the screen shot but it was mostly 88 for the journey that I logged.

So true that if I let the car warm up for a few minutes than theres no problem. It's stated that you don't need to warm up the car for more than one minute so I would have thought that the car would be able to cope with this electrical load before it's fully warmed up.

**integral90** · 16-06-2009 02:02 PM

Originally Posted by unity

How do you manage to keep your coolant under 90? Mine was noted at 90 in the screen shot but it was mostly 88 for the journey that I logged.

So true that if I let the car warm up for a few minutes than theres no problem. It's stated that you don't need to warm up the car for more than one minute so I would have thought that the car would be able to cope with this electrical load before it's fully warmed up.

hehe, I usually drive with the heater on. And make sure the last few km of a journey I don't go WOT or rev high.

Could your alternator be on the way out? Maybe you should upgrade to a K20A accessory pulley

**unity** · 16-06-2009 03:01 PM

Originally Posted by integral90

hehe, I usually drive with the heater on. And make sure the last few km of a journey I don't go WOT or rev high.

Could your alternator be on the way out? Maybe you should upgrade to a K20A accessory pulley

Okay. Interesting. I'll drive one day with the heater on full and see exactly how much a difference it makes to the operating coolant temperature.

So what's the issue with a higher coolant temperature? Does this affect the efficency of the engine?

What's the difference between the K20A accessory pulley and the one that comes stock on the car? I'll get it to the dealer sooner or later. It's just not convient at the moment to have to leave my car overnight with the dealer.

**CRXer** · 16-06-2009 03:16 PM

the question is,how long did the 11.6V occur for?,if its just a logged minimum value spike,dont worry about it.

at 90deg your motor is in perfect operating range,again dont worry about it.

i think u should put scanner away till real problem occurs,its like someone who just sneezed & after reading the internet they think they are dying from brain tumor

**unity** · 16-06-2009 04:27 PM

Originally Posted by CRXer

the question is,how long did the 11.6V occur for?,if its just a logged minimum value spike,dont worry about it.

at 90deg your motor is in perfect operating range,again dont worry about it.

i think u should put scanner away till real problem occurs,its like someone who just sneezed & after reading the internet they think they are dying from brain tumor

Yeah it was just a spike. Not a constant low voltage. However, I'm sure there is a gremlin somewhere in my car. I just haven't found it yet. I'm sure the problem I'm having with my SRS light upon start up is of an electrical nature.

It's also a good noob tool. You never learn anything if you never ask "who", "what", "where", when"' "why" and "how".