 | Home > In Car Electronics > Supply permanent live to headunit during cranking |
 
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20359  
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Sounds normal to me, you'll also maybe notice there may be a voltage increase when the revs go up. $W33T $0U7H3RN $UG4R
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24th Mar 2014 2:21pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5699 
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It's very different characteristics to the Td5. And not sure it can be completely normal that it sets of the alarm on the monitor. It also takes longer than I would have thought to return to a decent level once engine has started. How much control does the ECU have on the alternator? I would not have thought any control.
Andy |
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24th Mar 2014 8:14pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20359
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No control, when you say alarm do you mean the vehicle alarm?
Sounds a little like it might be the battery that needs testing and possibly replacing. $W33T $0U7H3RN $UG4R 🇬🇧🏴🏴🏴🇮🇪🇺🇸⛽️🛢️⚙️🧰💪 |
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24th Mar 2014 10:09pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5699
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Not vehicle alarm but alarm on battery monitor. Batteries are oddesey and in good order, must just be a quirk of the Tdci.
Just thought it may have been the same reason as the topic starter, due to the period of time of low voltage after start. Andy |
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24th Mar 2014 10:28pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20359
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Are you running a twin battery set up then? $W33T $0U7H3RN $UG4R
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24th Mar 2014 10:34pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5699
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Yep
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24th Mar 2014 10:35pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20359
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If your running a split charge I'd imagine it's because the alternator has to work harder to charge than a single battery.
If twin battery's have more juice to give on starting but as they are depleted take more to charge up. Slight delay in this, same as a single battery behaviour but exaggerated. I notice even with mine if the hazards are on each flash the headlights ever so slightly dip each time due to voltage drop. Soon cure that by going LED but I'd imagine your issues are down to the twin battery set up. I'm not an expert though.. $W33T $0U7H3RN $UG4R 🇬🇧🏴🏴🏴🇮🇪🇺🇸⛽️🛢️⚙️🧰💪 |
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24th Mar 2014 10:40pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5699
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At point of start batteries are not joined, and only main battery drops, once started and voltage high enough you can then hear relay kick in and join them.
I have also started a post in the Tdci section, mentioning this, and have also included a photo of glow plug connection that doesn't look happy. Am thinking possible related! Andy |
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24th Mar 2014 10:57pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 20359
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Ah I see, I didn't know that. $W33T $0U7H3RN $UG4R
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24th Mar 2014 11:57pm |
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| munch90 Member Since: 26 Oct 2013 Location: guildford Posts: 3558 
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anyone get to the bottom of this
i got much the same problem ( if its a problem , but its drive me mad ) thinking maybe add a small battery just wired to headunit ( to kept radio live while cranking ) and fit a smartcom relay to charge it when engine running ? any other ideas out there done so far heavier wire to radio delay off relay to keep ign feed live while cranking ( but seems to be voltage drop problem and hu drops out ) new bigger battery got idea of adding a small battery only wired to radio ( so will only run radio nothing else ) maybe motorbike battery say 12v 20ah so will run radio for a while without engine running and be charged ( and radio powered ) via smartcom relay when engine is running wiring small battery positive to radio perm feed and ign feed (ign feed switched via standard relay switched by standard wiring so will go on and off as normal negitive to body ( to save running extra neg to head unit ) wire from main battery via smartcom relay to small battery to charge reason for only running a small second battery , second small battery is only going to power radio when engine not running if parked up , power radio during cranking , keep radio memory live when parked up and switched off and small battery will be disconnected from starting battery while cranking by the smartcom relay any thoughts on this ? Last edited by munch90 on 22nd Feb 2015 10:23am. Edited 1 time in total |
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22nd Feb 2015 7:26am |
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| munch90 Member Since: 26 Oct 2013 Location: guildford Posts: 3558
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anyone have any ideas / can see problems etc with above idea ?
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22nd Feb 2015 10:18am |
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| mrd1990 Member Since: 16 Aug 2012 Location: Wales Posts: 600  
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I did some experimenting and found two things are causing the problem, ignition feed goes off during cranking and voltage drops too much from the permanent live.
Ignition feed isn't a problem, I'm sure all head unit resume straight away. The only realistic way around the voltage drop is a second battery. If you use a split charge system this should work, you can have the radio on with position 1 without draining the engine battery 
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22nd Feb 2015 11:45am |
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| Green Machine Member Since: 19 Nov 2010 Location: North Yorkshire Posts: 1226 
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Excuse the ignorance, but isn't the simplest solution to this just to manually switch the HU off before switching ignition off when parking up, and then turning it back on manually after start-up? The voltage drop of start up has caused problems with my Kenwood HU (amongst a whole load of other problems with it!), so I'm now in the habit of doing the above. Sounds like a faff, but once you're in the habit of doing it you don't think about it. 2005 Td5 | 90 Station Wagon | Tonga Green
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22nd Feb 2015 12:11pm |
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| dgardel Member Since: 30 Nov 2008 Location: Veneto (Heart & Head) Posts: 3586 
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easiest way Phonocar 5/146
http://www.phonocar.it/en/accessories/elec...5-146.html Click image to enlarge I solved with it Discovery 5 td6 HSE Stornoway Gray Outback Engineering Limited Edition
IID Pro MV License |
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22nd Feb 2015 12:59pm |
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