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Hot Rods 6v to 12v

Discussion in 'The Hokey Ass Message Board' started by easyrider47, Sep 30, 2020.

  1. easyrider47
    Joined: May 7, 2004
    Posts: 627


    I have blaycock overdrive from a volvo in my Model A. It's designed to work on 12 v. but mine don't. I can put my 12v charger on the solenoid and it clicks. What type of convertor can I get to convert 6v to 12v ? I don't want to switch the whole system to 12v.
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 5,329


    You need to know the current draw the solenoid uses, then account for inrush current, I forget off the top of my head what is normal for a solenoid, may @Crazy Steve will chime in. Then most converters, etc are rated in power (watts) so then do a little math where power/voltage=current to see if the one you are selecting is up to the task.

    I meant to add, if the inrush current is 20 amps, yet draw is 7 amps (both most likely higher than you'd have) you don't need a converter capable of 20 amps, probably a 10 amp rated continuous output would be fine.
  3. This might work....
    The catch is how much current the solenoid pulls when switched on, and particularly how much inrush current it has. A solenoid is technically a motor, and electric motors can instantaneously draw up to 1200% of running current on initial start-up, and 300% for a measurable time. This convertor is rated for up to 10 amps, but how sensitive it is to transient current spikes before it's auto-shutoff feature works is unknown, and also if it can withstand them without failing if it doesn't shut off. Electronics generally don't like big spikes in either voltage or current.

    Best advice I can give is to get an accurate measurement of the solenoid 'running' current, multiply that times 3, and if the number you get is 5 amps or less, this might work. This is the largest unit I'm seeing, if this doesn't work you'll probably have to track down a 6V solenoid that will fit. I suspect that will be the final solution... or you'll have to bite the bullet and convert to 12V.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 47,498


    I'd start with a 20 amp converter, just because you don't want to have to order a second one when the 10A unit doesn't do the job.

    how would you measure inrush current?

  5. 58 Mustang
    Joined: Sep 4, 2020
    Posts: 25

    58 Mustang

    I used to work on British cars which often Had Laycock DeNormanville overdrives. When to double the volts from 6 to 12, you lose half of the amps. You need a fair amount of amperage to hold the solenoid in the engaged position
  6. Jim, I didn't find a bigger unit. There's some 12V to 6V units that output that much, but it's the wrong direction. I thought about possibly paralleling two of these 10A units, but I'd be concerned with interaction between the electronics in two units. You just might kill two units instead of one...

    For a DIY guy, accurately measuring inrush is pretty much impossible. It can be done with a O-scope, and I've seen portable meters with a peak hold feature that could possible do it with somewhat reasonable accuracy but those are big $$$$ units. Even measuring the 'on' current with accuracy isn't easy as most meters aren't that sensitive at that scale. I figure that 300% of the 'on' current would at least get him in the ballpark, beyond that it comes down to where the unit protection thresholds are set and how sensitive they are. My personal experience with these is they really don't like current spikes of any large magnitude even if it supposedly doesn't exceed their capacity as they 'see' them as a short and shut down.
    squirrel likes this.
  7. BJR
    Joined: Mar 11, 2005
    Posts: 6,712


    Why not just put a garden tractor 12 volt battery in the trunk to run the overdrive, and just charge it when not in use.
    firstinsteele and pprather like this.
  8. easyrider47
    Joined: May 7, 2004
    Posts: 627


    I think that may be the easiest BJR
    BJR likes this.

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