Battery On/Off Switch Project - completed

jbeletti, while perusing your photos again in preparation for my purchasing of a disconnect switch like yours, I noticed that your "Power King" battery is a marine deep-cycle battery. Your battery is not the true deep-cycle type that is best suited for our RVs. The marine batteries are more akin to automobile batteries and have a much shorter life span than true deep-cycle batteries. The primary advantage of a true deep-cycle battery is that it may be discharged way down (i.e., deep-cycled) without the damage that would occur if you did this with your marine battery. For a good source of information about deep-cycle batteries, read the FAQs at:

http://www.windsun.com/Batteries/Bat...le%20Batteries

Windbreaker, an electrical engineer like Bill will be better qualified to answer your question than me. My stab at a response to your question, however, is that most household switches are usually rated at 20 amps of current. Since the current being drawn from the battery may exceed this at certain times, there may be a danger of overheating the switch (the heat generated within an electrical component is directly proportional to the current multiplied by the resistance squared). You may get away with using a 115v household switch but it's better to use a heavy-duty switch made for the specific purpose. After all, severe electrical overheating can lead to a fire inside your trailer.
Larry

[jbeletti]

Hi Larry,

Thanks for your comment on my battery. It's what my dealer supplies with his trailer prep, so it's nothing I had a say in, nor would I have been informed enough at that time to even ask about something different. When I eventually kill this battery, I'll probably replace it with a couple of 6 volt deep-cycle units as the running commentary seems to favor this arrangement. I have a contact that will allow me to purchase at a very good discount as well, so this should help offset the incremental cost of the 2 battery arrangement. Thanks again.

Followed your excellent directions today and installed the battery shut off switch. Your directions were very clear and the project was easy. Didn't need the 30 amp in line fuse as the 2005 3023 had one installed already about 6 inches down the cable on the + side.

Thank you very much,

John

[Bill]

Originally Posted by Larry_Loo

Windbreaker, an electrical engineer like Bill will be better qualified to answer your question than me. My stab at a response to your question, however, is that most household switches are usually rated at 20 amps of current. Since the current being drawn from the battery may exceed this at certain times, there may be a danger of overheating the switch (the heat generated within an electrical component is directly proportional to the current multiplied by the resistance squared). You may get away with using a 115v household switch but it's better to use a heavy-duty switch made for the specific purpose. After all, severe electrical overheating can lead to a fire inside your trailer.

Larry has it exactly right - almost. Actually, most household light switches are rated at 15 amps, rather than 20 amps. Since the TM battery current can approach 30 amps at times (limited only by the 30-amp fuse), there is some risk of overheating the switch. A marine switch, as Jim B described, is really a good way to go since it is intended for this application, and is generally weather-resistant and vibration-resistant, as a household switch is NOT. And since it is only a few bucks more, I would not skimp.

And Larry, power is currrent-squared times resistance, not the other way around. Most likely a typo.

Finally, a minor nit for Jim. Your 4th picture shows the red wires crimped into the ring-tongue lugs. Although commercial crimp connections made with special tools are perfectly reliable (your car has literally hundreds of crimp connections, and they all last for 20 years), I have come to distrust homemade crimps made with hardware-store crimp tools. They just are not reliable, because the tool just cannot create enough force in the proper pattern. Try grabbing the ring lug with a pair of pliers and pulling hard on the red wire with your other hand. I bet the wire pulls right out of the crimp, and it shouldn't. I always crimp first, and then solder. I admit I am a belt-and-suspenders guy - but it makes me more comfortable.

Otherwise, nice installation!

Bill

I decided to post this update on how my Concorde AGM battery and marine disconnect switch are faring because I've been impressed with the battery's performance in storage. Last week I decided it was time to check my TM's battery, a Concorde absorbed glass mat (AGM) deep-cycle one. Voltage across the terminal posts was 12.58 volts. This nearly floored me since the battery hadn't received a charge for at least 6 possibly 7 months (I'm not very diligent with preventive maintenance). When fully charged, its voltage has been about 13.08 volts. I've had the battery disconnected, of course, from all parasitic loads by keeping its marine disconnect switch in the "Off" position. That's a half volt decrease over the 6 or 7 months, an extremely small drop per month due to internal losses. In contrast, over a year ago this same battery's voltage dropped to about 10.5 volts during a storage period of about the same length of time. At that time it was connected to all of the TM's parasitic loads since I had not installed a disconnect switch. Then I was really worried that I had killed my battery through neglect but a charger brought it back nicely to full voltage.

The combination of an AGM battery and a marine disconnect switch seems to work very well when a trailer is sitting idle.

[Leslie & Nick]

I like those sealed, glass mat batteries too! I had one in a Miata. The battery was in the trunk compartment, so it was important that it didn't leak or "gas off". Unfortunately, I was sidelined with an injury for several months and could not drive the car, and the four year old battery did die on me. Should have had somebody start the car every month or so.

This is one of my next projects, as soon as I figure out where to mount the switch. I have the 2720 with swing away tongue, So I need to mount it on the tongue somewhere. I'd like to find a covered weather proof box, somewhat like a "bell" box for outdoor electrical. I'd like the switch to be covered from mud and rain, but easily accessible. The wiring behind the switch should be out of direct rain and mud. I'm not worried about fog and moisture.

[I responded to the topic, not realizing there was a second page of responses, but just to expand some more...]

A house switch isn't designed for the potential current flow.

In a house, as an example, the most you'd want to switch is approx 1800 watts, which = 120 volts X 15 amps. That same load (1800 watts) = 12 volts X 150 amps! You're talking some serious current flow and some serious arcing if you switch off that load; of couse if you turn everything off before you turn your battery switch off, you might get away with it (for a short period of time).

The battery switches are also designed so that sparking (while switching) is concealed so as not to ignite battery and or other fuel fumes, unlike a house switch.