Anatomy of a (failed) battery disconnect switch

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Anatomy of a (failed) battery disconnect switch

March 14, 2020, 08:21:29 pm

The disconnect switch option between the standard pair of 6V batteries can - and usually will - eventually make poor contact, causing a variety of potential problems. In this case, under heavy current demand, the battery voltage will drop. For instance, as happened to us, in trying to start the generator, the starter would turn it over easily but it would take a long time for the ignition to start it running.

The switch halves are held together by a couple of open rivets that also serve as switch mounting holes. By drilling out these rivets, I could separate the two parts to examine the contact surfaces. Mounted again with the screws, the switch will still function properly. I noted only carbon spots on the contacts from arcing over time, creating resistance, but no signs of contamination or deterioration from battery fumes. The activation lever simply pushes a shorting bar across the terminal contacts, under spring pressure. I have included some pics, showing components, the carbon spots, and cleaning result using a sharpable ink eraser and alcohol.

Though not a firm indication of performance under load, I measured my meter probe resistance as 0.1 Ohm, and it did not change probing the closed switch.

Steve

Re: Anatomy of a (failed) battery disconnect switch

Reply #1 – March 14, 2020, 09:57:52 pm

Good information--thanks, Steve!

Re: Anatomy of a (failed) battery disconnect switch

Reply #2 – March 14, 2020, 10:52:53 pm

Sure looks like the one I got at Harbor Freight.

Re: Anatomy of a (failed) battery disconnect switch

Reply #3 – March 15, 2020, 01:26:46 am

Steve, how old is that disconnect switch?
Jane

Re: Anatomy of a (failed) battery disconnect switch

Reply #4 – March 15, 2020, 10:48:17 am

Quote from: Jane and Scott - March 15, 2020, 01:26:46 am

Steve, how old is that disconnect switch?
Jane

2004 - it came from the factory that way, I assume. We purchased the rig in 2012.

Steve

Re: Anatomy of a (failed) battery disconnect switch

Reply #5 – March 15, 2020, 12:27:01 pm

Thanks for the teardown. It doesn't seem to take much carbon build up to cause problems .
As we have disused before, it's a cheap switch. True heavy-duty battery switches have corrosion-resistant, metal coated contacts, usually a silver alloy, while the Factory Hella switch does not. At least, it's not difficult to open up and clean the contacts.
I have search for years for a high quality direct replacement without success.

Larry

Re: Anatomy of a (failed) battery disconnect switch

Reply #6 – March 15, 2020, 12:45:02 pm

On our little work boat, the battery switches are located on a bulkhead where there is often heat, high humidity and seawater. After 15 years, I have never had a battery master switch go bad.

How about this?

Blue Sea Systems - Manual 300 Amp "e-Series" - Battery Switches - Switches -...

A B.O.A.T. unit is $1000. Break Out Another Thousand. At less than $40 for the switch, it isn't even 1/20 of a BOAT unit. ABYC pieces and bits are typically good quality and hold up in wet environments.

Harold

Re: Anatomy of a (failed) battery disconnect switch

Reply #7 – March 15, 2020, 12:57:55 pm

The switch I disassembled makes contact simply by push-contact under spring pressure. This is a bad design, since the contacts are not self cleaning. Better designs use a sliding set of contacts, such as a knife switch. Since the marine switch is a rotary one, perhaps it would avoid the issue I found. However, at over 3.5" diameter and almost 2.5" deep, it may not be possible to find a useful mounting spot in the battery compartment.

Steve

Re: Anatomy of a (failed) battery disconnect switch

Reply #8 – March 15, 2020, 01:06:08 pm

Quote from: Blueox25 - March 15, 2020, 12:45:02 pm

On our little work boat, the battery switches are located on a bulkhead where there is often heat, high humidity and seawater. After 15 years, I have never had a battery master switch go bad.
How about this?
Blue Sea Systems - Manual 300 Amp "e-Series" - Battery Switches - Switches -...

Our LD has used a marine switch for 15 trouble-free years. it's the way to go if rewiring or seriously upgrading the electrical system.

Completed electrical/propane compartment | Compartment now h… | Flickr

Larry

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