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Date:         Sun, 2 Aug 2015 13:08:24 -1000
Reply-To:     "SDF ( aka ;jim lahey' - Scott )" <scottdaniel@TURBOVANS.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "SDF ( aka ;jim lahey' - Scott )" <scottdaniel@TURBOVANS.COM>
Organization: Cosmic Reminders
Subject:      Re: fridge relay nightmare !
Comments: To: Christophe Guilbert <cguilbert@PICASSO.UCSF.EDU>
In-Reply-To:  <55BE9DC2.7030500@picasso.ucsf.edu>
Content-Type: text/plain; charset=utf-8; format=flowed

see if this helps....

you nailed this part for sure .. " Term 85 , red/black wire, goes to ground starter solenoid, is +12V ONLY when starter is cranking , it is ground otherwise ( before running the starter and once the engine is running). "

Perfect so far on that side of the relay. If there is good voltage opposite of pin 35 ...it will 'see' ground as you mention here. ( ..after the ignition swithch is release back to 'on' from start ) thus engerizing the coil in the relay so that it's energized. In the stock configuration Charging voltage is then sent to the Aux Battery. Which is exactly what one would want ... the Aux Battery is isolated until after the alternator is charging.

I would just put 'good voltage' on pin 86 ..and see if the relay energizes with engine running and alternator charging ..it sure should.

fwiw..I believe the blue wire is the same small blue wire that goes to the alternator small warning light/excitation small terminal.

I wonder if you are trying to use this Aux Battery charging relay in a way that may not work.

Sounds to me what you want is a load reduction relay .. or an isolation relay ..such that your electronics are powered up only during key on or running. ..I would just connect to X contact at the ignition switch ...the same X contact that supplies power to wipers and headlights .. such that key on ..they get power .. during 'start' they do not .. once running they do.

On 8/2/2015 12:46 PM, Christophe Guilbert wrote: > Hi guys, > > I am adding a secondary battery and 6 various gauges , I already started > an ambitious project to rewire the camper and dashboard accessories > dramatically. For that I am re-purposing the fridge relay which protect > the electronics when the starter kick in. > > I spent hours trying to understand it but I still don't have a clear > view how it works especially when my voltmeter does not show what is > expected and my Bentley does not cover it. > > Here is my understanding of how the two wires triggering the relay is > working, please correct me if I am wrong. > > - Term 86, blue wire , goes to ignition switch , is over +10V when the > alternator is running which mean that it is over +10V when cranking the > starter and of course over 10V when the engine is running. I found > conflicting information about this blue wire, some people said in should > be +1.5V (from the instrument cluster alt warning circuit) when the key > is in the switch on position (just before the starter crank) and the > engine stopped; some other people said we won't have + voltage. In my > case I have 0.07V with no key and 0.2V at the switch on position and > around 1V at the cranking stage than 0.2V again with the engine running. > This is Grey area I really would like someone to explain me. > > - Term 85 , red/black wire, goes to ground starter solenoid, is +12V > ONLY when starter is cranking , it is ground otherwise ( before running > the starter and once the engine is running). > > Term 87a (water pump and LED panel) is connected to Term 87 (constant > +12V input). > > Term 30 goes to the fridge > > When the relay is not energized , 87 -> 87a , when the relay is > energized, 87 -> 30 but 87 still connected to 87a > > On my relay currant flows (electron wise) from term 85 (-, red/black > wire) to term 86 (+, blue wire) and not the other way around , the relay > must have a diode. > > So here are the sequences of event, > > 1) When no key, 85 is 0v , 86 is 0v, term 87 being connected by default > to 87a , 87a (water pump and LED panel) receive +12V from 87 , term 30 > (fridge) is 0V not working > 2) When putting key and switch to the on position while engine stopped , > 86 is supposed to be +1.5V and 85 is 0V (grounded), same effect as 1) > anyway because 87 and 87a are connected regardless of the relay state > and 1.5V different between 85 and 86 is not enough to trigger the relay > and close 87 with 30 (fridge) > 3) Engine crank, starter working, the alternator and battery is running, > 86 is +10V. 85 (which was grounded in step 1) and 2)) become +12V and > counterbalance the +10V of 86. Since there's a diode preventing flow > from 85 to 86, the voltage different between 85 and 86 is 0V and the > relay in not energized , terminal 30 (fridge) is not closed with 87. The > fridge is not working during the cranking process. > 4) After the cranking and engine running , 86 re-become +0V and 85 is > +10V, the relay is energized and the fridge is working trough term 30 > > Correct me if I am wrong but the trick here to isolate the fridge during > the cranking seem to be the fact that the blue wire term 85 is +10 V < > +12V term 86 when the starter work. I supposed that the 1.5V you see in > step 2 was "removed" by the instrument cluster for the purpose of > having 10V > > I you read that far without too much headache , thank you so much ! ;-) > So why all this , well I like to idea of isolated my instrument during > the cranking process and this is a nice way of doing so, I also wanted > to be sure I understood correctly because I don't have +10V in my blue > wire right now , maybe it is due to the fact that my instrument cluster > is unplugged , I need to find out. > > Thanks >


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