The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: BooG on September 13, 2012, 07:44:12 AM

Title: Turnover from wall socket
Post by: BooG on September 13, 2012, 07:44:12 AM

I'm sure I read somewhere that someone had made a transformer type thing so when you need to turn the engine over, it doesn't run the battery down constantly. It plugged into the wall, through the transformer, and straight onto the bike. Anyone else remember that?

Title: Re: Turnover from wall socket
Post by: Bob_Roller on September 13, 2012, 09:40:25 AM

I haven't heard of anything like that, it needs to put out in the area of 120 amps for starter operation .

Title: Re: Turnover from wall socket
Post by: nhmaf on September 13, 2012, 10:40:36 AM

If it were just a transformer with diode bridge for 12V DC output, it would have to be approximately 1.5KVA unit, which would weigh around 30-40 pounds.   If one had a LARGE battery charger (as used for large trucks/farm equipment, and no, I don't mean a "trickle charger") that might also work.

Title: Re: Turnover from wall socket
Post by: Barry on September 13, 2012, 12:08:49 PM

I've sometime turned the engine over with an ordinary automatic  8 amp battery charger attached. All that happens is the charger goes to full output as the voltage at the battery terminals drops during cranking. It helps a little but no use pretending it provides even 10% of the starting current.  Leaving it connected after cranking and watching the charge current fall tells you that the battery drain is being replenished.  It just occurred to me that many modern battery chargers have no ammeter fitted relying instead on a charge completion light.  Where's the fun in that ? I want to see the ammeter needle fall which tells me the battery voltage is coming up.


I would be careful about connecting a really big charger when not actually cranking as you don't want the charge current to exceed 10% of the Battery amp hour rating for any length of time. I often wonder what the amp hour rating of my 10 year old Varta wet cell actually is. Probably less than half of it's original 18 AH so I set the maximum charge current accordingly.  

Title: Re: Turnover from wall socket
Post by: tvrla on September 13, 2012, 09:51:14 PM

Sometimes I've started the bike with the battery charger set to the START function. I think it's fifty amps. If the battery isn't too low, that works.

If not, put it on the 2 amp setting for a bit, then retry.