Test your battery switch

[Ed Haley]

In a few earlier messages, there was a question of whether it was safe to switch from one battery to another or to both using the ship's battery switch while the engine is running. Of course, any interruption of the charging current into any battery for even an instant can fry your alternator. One way to test your switch to see if the contacts of the switch make before break is to use an electronic device such as an autopilot or loran that uses battery power (without the engine running). Turn on the autopilot or loran (even in your slip) and get it functioning. Then switch your battery switch from 1 to 2 and to all and back again. If the electronic equipment senses any interruption of electric energy at all (even a millisecond) you will detect an abberation in function. If this happens, I would advise never to switch batteries while the engine is running.



eghaley@dreamscape.com

[D. Stump, Hanalei]

Ed,
I posted the question earllier. Thanks for your comment, I'll try it this weekend. I was going to break out the VOM and test the back of the switch, but your method sounds a lot quicker. Thanks again!!!

[Jon Larson]

Another way is to switch between settings with the VHF on, any corrosion or breaks in the switching will be heard as static in the VHF. At least it does on the old VHF on PERI. I do periodically check this and every once in a while I've got to wipe the switch back and forth to wear stuff off the contacts.

My GPS is backed up with batteries, I'm not sure it would indicate a break in the power as a result of switching the main switch, so be careful of the electronic gear you are doing the testing with if that's the way you are doing it.

Jon Larson
Cape Dory 30 PERI
San Francisco Bay

In a few earlier messages, there was a question of whether it was safe to switch from one battery to another or to both using the ship's battery switch while the engine is running. Of course, any interruption of the charging current into any battery for even an instant can fry your alternator. One way to test your switch to see if the contacts of the switch make before break is to use an electronic device such as an autopilot or loran that uses battery power (without the engine running). Turn on the autopilot or loran (even in your slip) and get it functioning. Then switch your battery switch from 1 to 2 and to all and back again. If the electronic equipment senses any interruption of electric energy at all (even a millisecond) you will detect an abberation in function. If this happens, I would advise never to switch batteries while the engine is running.

jon9@ix.netcom.com

[Stephen]

I'm not sure this is such a good idea. If your electronic unit has batteries or a built-in voltage regulator including a capacitor, I don't think you would detect anything. Your best bet would be to use a sensitive analog multi-meter. You should see the needle drop when the current is broken.

Another way to check would be to call the switch manufacturer and ask them whether it is make before break.



sailing@star.net

[Larry DeMers]

Guys..I have a 1983 CD30, and the battery switch IS NOT a make-before-break switch..based on the fact that someone aboard *did* the deed..switched the damn switch, thus allowing me the pleasure of spending a day rebuilding my alternator (not hard). I had to replace all diodes and the regulator board.Now it works perfectly. I have checked the switch with a Fluke Digital Multimeter and saw no break in the voltage source as I went from 1 to 2, but this may be due to capacitances in the distribution of the 12v (some device may have been holding the 12v up between switch movements making it seem that the contact was a make-before-break type). Assume that it is not wise to make a battery switch change with the engine running until you are certain that the switch will not interrupt the batteries load.
What about switches that have an integrated field switch built in? That would seem the surest way to go. The field switch opens on every change in position of the switch, thus turning the alternator off for an instant. In order to make it work with an alternator that has an internal regulator, the field winding wire will have to be opened (not a problem..it is one of a few wires in the alternator and is clearly identified in the 12v Dr's. handbook on alternators as well as Nigel Calders book) and then led outside of the alternator and connectorized with a bullet connector or something. But this would be a sure way to control the alt.

Good Luck!

Larry DeMers
s/v DeLaMer
CD30 sailing Lake Superior



demers@cray.com