variable voltage ?

sparky2 · 12-03-2007, 23:56

Has anybody noticed that the interior heater fan runs fairly slow even on its highest setting ? if like me you then reverse into your drive the fan suddenly goes into its proper full speed

so what happens when you select reverse, does it disconnect the power steering which is electrically driven ? I havent measured the voltage but it does seem to increase when reversing.

Conshine · 13-03-2007, 01:07

My fan runs fairly fast at the highest setting, 4 blows quite a bit.

The power steering wont stop, it's electrohydraulic so there is power to it all of the time, I think the hydraulic pump is electrically driven, it just adjusts the response at various speeds, more responsive at lower speed for parking etc.

If you have a Diesel like me, the fan will go into interior recirculation mode to stop fumes entering the cabin while going backwards so the fan will speed up anyway.

The volts shouldn't increase anyway, the car runs on 12 volts, so the motor speed will increase and decrease via a variable resister which adjusts the current flow, not the volts. There is plenty of juice available from the alternator for what the car requires.

Does your fan work on all 4 speeds? sounds like the switch may be playing about?

Td-eye · 13-03-2007, 06:41

Quote:

Originally Posted by sparky2

Has anybody noticed that the interior heater fan runs fairly slow even on its highest setting ? if like me you then reverse into your drive the fan suddenly goes into its proper full speed

so what happens when you select reverse, does it disconnect the power steering which is electrically driven ? I havent measured the voltage but it does seem to increase when reversing.

The fan goes into recirculating mode when you select reverse so that you don't suck exhaust fumes into the car.

sparky2 · 13-03-2007, 11:02

Thanks for that lads, I wonder if the cabin filter needs changing as it would be bypassed when its in reverse and resurculating ? but when I reverse the reversing lights flicker as though its dragging the volts down as I turn the steering, wasn't there a problem with the battery or alternator ? cheers - Stuart.

Conshine · 13-03-2007, 11:34

The alternator is self exciting and will not run at full output when on tickover, it runs at around 12volts, but to overcome the volts coming from the battery, it needs to output 13.2V minimum as this is what volts a 6 cell battery will produce in good condition, so essentially, the power is coming from the battery and not the alternator for a short time until you touch the pedal.

Get a garage to do a drop test on the barttery if all else fails.

I would think the pump for the steering uses quite alot of power.

Try it, put a voltmeter on the battery terminals at tickover and at fast idle and you can see the difference.

12-03-2007, 23:56	#1
sparky2 Briskodian Join Date: Jan 2005 Location: Manchester UK Posts: 259 Members Car: Octavia TDi (me),Fabia TDi (wife),Fabia VRS SE (son) Thanks: 2 Thanked 6 Times in 5 Posts	variable voltage ? Has anybody noticed that the interior heater fan runs fairly slow even on its highest setting ? if like me you then reverse into your drive the fan suddenly goes into its proper full speed so what happens when you select reverse, does it disconnect the power steering which is electrically driven ? I havent measured the voltage but it does seem to increase when reversing.

13-03-2007, 01:07	#2
Conshine Ho Ho Ho Join Date: Feb 2007 Location: Ashford, Kent Posts: 1,904 Members Car: Silver Fabia vRS Thanks: 102 Thanked 56 Times in 56 Posts	Re: variable voltage ? My fan runs fairly fast at the highest setting, 4 blows quite a bit. The power steering wont stop, it's electrohydraulic so there is power to it all of the time, I think the hydraulic pump is electrically driven, it just adjusts the response at various speeds, more responsive at lower speed for parking etc. If you have a Diesel like me, the fan will go into interior recirculation mode to stop fumes entering the cabin while going backwards so the fan will speed up anyway. The volts shouldn't increase anyway, the car runs on 12 volts, so the motor speed will increase and decrease via a variable resister which adjusts the current flow, not the volts. There is plenty of juice available from the alternator for what the car requires. Does your fan work on all 4 speeds? sounds like the switch may be playing about? __________________ Ben Last edited by Conshine; 13-03-2007 at 01:24. Reason: Change text

13-03-2007, 11:02	#4
sparky2 Briskodian Join Date: Jan 2005 Location: Manchester UK Posts: 259 Members Car: Octavia TDi (me),Fabia TDi (wife),Fabia VRS SE (son) Thanks: 2 Thanked 6 Times in 5 Posts	Re: variable voltage ? Thanks for that lads, I wonder if the cabin filter needs changing as it would be bypassed when its in reverse and resurculating ? but when I reverse the reversing lights flicker as though its dragging the volts down as I turn the steering, wasn't there a problem with the battery or alternator ? cheers - Stuart.

13-03-2007, 11:34	#5
Conshine Ho Ho Ho Join Date: Feb 2007 Location: Ashford, Kent Posts: 1,904 Members Car: Silver Fabia vRS Thanks: 102 Thanked 56 Times in 56 Posts	Re: variable voltage ? The alternator is self exciting and will not run at full output when on tickover, it runs at around 12volts, but to overcome the volts coming from the battery, it needs to output 13.2V minimum as this is what volts a 6 cell battery will produce in good condition, so essentially, the power is coming from the battery and not the alternator for a short time until you touch the pedal. Get a garage to do a drop test on the barttery if all else fails. I would think the pump for the steering uses quite alot of power. Try it, put a voltmeter on the battery terminals at tickover and at fast idle and you can see the difference. __________________ Ben

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