Changing Ohm load using relays
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=27
Printed Date: April 24, 2024 at 9:02 PM
Topic: Changing Ohm load using relays
Posted By: jtf78
Subject: Changing Ohm load using relays
Date Posted: March 11, 2002 at 11:39 AM
I wanted to know how to setup switchable ohm loads when using dual voice coils subwoffers. I have seen this before where a switch on the dash changes the sub configuration from 8ohm to 2 ohm. Any one have a diagram or some insight? Thanks. ------------- Jerry
Replies:
Posted By: the12volt
Date Posted: March 11, 2002 at 11:43 AM
Hi jtf78, I beleive this is what you're referring to here: 
To read more about it, go here: https://www.the12volt.com/relays/page5.asp#stbm If this is not what you're looking for, please lets us know. the12volt
Posted By: jtf78
Date Posted: March 11, 2002 at 11:57 AM
I did see this but this is not exactly what I was looking for. I wanted to hook up a switch so that when going from sound quality competition to SPL I could set the subs to a difference resistance (2ohm at SPL and 8ohm at SQ). Normally whne wiring the DVC subs you can choose which ohm load you want by wiring the subs together in the box but I wasnt to switch them between competitions. I have seen this done before at a show but I never found the owner to find out how it was done. ------------- Jerry
Posted By: the12volt
Date Posted: March 11, 2002 at 12:10 PM
I see what you want to do...give me a little bit to draw up a diagram for you. I'll post here as soon as it's done. the12volt
Posted By: the12volt
Date Posted: March 11, 2002 at 12:50 PM
Hi Jerry, try this out for size: 
When the relays are at rest (normally closed position) the woofer coils are wired in series. When ground is applied to each coil (energizing the relay coils), the voice coils are wired in parallel. With 2 four ohm voice coils you'll have an 8 ohm load at rest and a 2 ohm load when the relay coils are energized. For each dual voice coil woofer that you want to change from series to parallel, you'll need two relays for each. They can all be controlled from the same toggle switch. If you need anything else, let us know. the12volt
Posted By: jtf78
Date Posted: March 11, 2002 at 1:22 PM
Thanks for your help. That should work out well.
-------------
Jerry
Posted By: the12volt
Date Posted: March 11, 2002 at 1:24 PM
You're welcome ...glad I could help. the12volt
Posted By: bayvanman
Date Posted: March 19, 2002 at 4:36 PM
I'm new to the forum, and all I can say is... you have already answered my question before I asked it!!! THANK YOU!!!
Posted By: BlackGti
Date Posted: March 21, 2002 at 11:44 AM
what gains/losses do u get with this setup? and what subs/amps can u do this with...obviously DVC ones but which ones? ------------- Best Buy Mobile Install Tech.
Posted By: the12volt
Date Posted: March 21, 2002 at 1:43 PM
Hi BlackGti, you can use this on any amplifier capable of handling the lowest impedance level produced by the two given voice coils. What you gain in the example above with two 4 ohm voice coils is the ability to change from an 8 ohm load to a 2 ohm load at the flick of a switch allowing you to change from a setup geared towards sound quality to one geared towards loudness. the12volt
Posted By: chrispcwiz
Date Posted: April 03, 2002 at 6:22 AM
hi, what about power handling!!?? thise relays wont handle alot of power that way!!! chris
Posted By: wirewise
Date Posted: April 03, 2002 at 8:25 AM
Hey Chris, try this...according to Ohm's law (I = Square Root of (P / R)) at 500 watts at 4 ohms, current would be 11.2 amps, at 1000 watts at 4 ohms, current would be 15.8 amps and so on. Rated contact current capacity of a Bosch relay = 30 amps, Potter & Brumfield relay = 40 amps. Rated contact power capacity @14VDC = 500 watts...(500 watts@14VDC = toasted voice coil!) Power handling looks fine to me :) Try it yourself https://www.the12volt.com/ohm/page2.asp#12~~wirewise~~
Posted By: hot_shot_guy123
Date Posted: April 03, 2002 at 4:33 PM
This is a handy feature to have so you don't have to mess with setup.
Posted By: 2DamnLoud
Date Posted: April 03, 2002 at 9:41 PM
Have any of you ever actually tried this?!? 12 volt and ground running with the speaker wires in a magnetic relay,...... damn that's gotta be noisy
Posted By: wirewise
Date Posted: April 04, 2002 at 9:17 AM
Yup, no noise in either mode!
~~wirewise~~
Posted By: 2DamnLoud
Date Posted: April 08, 2002 at 9:28 PM
I've had the diagrams for a long time, never tried either though
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