Powering Shaved Door Solenoids through voltage drop.

Thread Starter

Matthew Paulin

Joined May 14, 2018
4
Hello Team,

I have a large electronic project I am working on to add touch sensors to pop (shaved door = no mechanical handles) door solenoids, but I am having issues with the solenoids working correctly. It seems that the solenoids draw a lot of power and after 4-5 times opening with the car off, they no longer work due to battery voltage drop.

Is there a circuit I can add to beef up the voltage when the battery drops below 12v? As in some sort of OpAmp/Regulator/buck converter circuit?

Side note, this is a show car that is only driven to car shows (maybe 3-4 times a month) so the car tends to be not running the majority of the time.

I usually have to keep a battery charger on it when I'm home, but this is not helpful if I am out at a show and leave it off all day. I assume that there is something drawing the battery down while it sits, also, but this is an incredibly complex vehicle and difficult to trace.

Thank you for your time.
 

MaxHeadRoom

Joined Jul 18, 2013
19,057
How come it is designed with power necessary when not in use, sound as though power is required to keep in activated position?
I would have thought that some kind of magnetic latch unlatch type of solenoid would be preferable.
Max.
 

Thread Starter

Matthew Paulin

Joined May 14, 2018
4
How come it is designed with power necessary when not in use, sound as though power is required to keep in activated position?
I would have thought that some kind of magnetic latch unlatch type of solenoid would be preferable.
Max.
They do not require power when not in use. They are just momentary solenoids that engage when they get 12 volts and stay engaged as long as you hold the button. But they draw power when engaged, and after engaging them several times with the car not running, they draw down the battery just enough that they stop working.
 

crutschow

Joined Mar 14, 2008
23,368
What is the battery voltage when the solenoids won't work?

Add another battery in parallel when at a show.

Add a very large capacitor in parallel with the battery to provide the momentary power required by the solenoid.

What size wire is going from the battery to the solenoids?
Larger wire could help.
 
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Thread Starter

Matthew Paulin

Joined May 14, 2018
4
Add a very large capacitor in parallel with the battery to provide the momentary power required by the solenoid.

What size wire is going from the battery to the solenoids?
Larger wire could help.
What is the battery voltage when the solenoids won't work?.
Voltage is around 10VDC when they stop working.

I believe that the wire is 10 or 12AWG. I'll check when I get home. And when you say 'Very Large Capacitor', can you help me narrow it down a bit? something like this?:

https://www.amazon.com/Belva-1-0-Farad-Power-Capacitor/dp/B00OYFVREA/ref=sr_1_2?ie=UTF8&qid=1526319448&sr=8-2&keywords=12+volt+capacitor

Thank you
 
Last edited:

crutschow

Joined Mar 14, 2008
23,368
Voltage is around 10VDC when they stop working.
That's a dead battery.
Those solenoids must draw a heck of a lot of current, if their occasional momentary operation causes a fully-charged auto battery to go dead. :eek:
I think either you have a bad battery or you have a short somewhere in the system that's drawing a lot of current.

Nothing that you can do will allow a car battery with a 10V open-circuit voltage to generate a significant amount of additional power.
 

Thread Starter

Matthew Paulin

Joined May 14, 2018
4
Ok so we just discovered that the issue is a poor ground. Ran the ground back to the neg battery terminal to test and they worked just fine. We originally grounded it to the chassis. Still might go with that Capacitor idea. Thanks for all your help :)
 

olphart

Joined Sep 22, 2012
78
Howdy, I once solved a solenoid actuated latch issue (distance vs pull strength).
I swapped the solenoid for a door lock actuator from a Mopar minivan.
They're a simple gear motor to rack (others are lead screw) that do similar function, but at Much less current.
I've also used a Blazer rear window latch release as a saddlebag latch (~2 yrs B4 A.Ness showed it).
If long term actuation is possible, put a "decent" capacitor (I used 68000uF) fed by a power resistor.
Size the capacitor to reliably actuate, the resistor to hold it open.
 

shortbus

Joined Sep 30, 2009
6,987
AND - Don't many cars use small motorized lead-screw actuators for door locks?
That is a rack and pinion actuator. May not be GM but looks like the ones they use. The O/P isn't doing a lock - unlock. He is pulling the latch mechanism to open a door with shaved/removed outside handles, a pretty common thing on custom cars. Usually with hidden switches, back in the day, but done now with remote lock fobs.
https://en.wikipedia.org/wiki/Shaved_doors
 

olphart

Joined Sep 22, 2012
78
Sorry Shortbus (Great Avatar) on any confusion.
I was allowing for a lead screw build, even though I've only seen / used rack & pinion units.
Amazon has RF remote relays well suited to a basic carrier control of a lock.
I'd insert a pulse sequencer in the tx, and pattern matcher (uC) in rx for Some security.
Maybe better -- replacement garage door opener remotes & associated relay contacts.

The rack & pinions I've used are an easy spring load to retract on deactivate.
It's why I favor the capacitor for actuate power pulse & current limiter resistor for hold.
The Blazer latched saddlebags were first shown at the '06 BMW National on (see attached):
Which was built in '03 -- Fun Toy. Good Hunting <<<)))
 

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