I have a question regarding toggle switches. I recently picked up a trolling motor for my boat and I wish to wire the motor up to two alternative source batteries, thus switching between them via a DPDT switch rather than physically unplugging them. The trolling motor manufacturer recommends a 50 amp fuse/breaker on the battery. Does this mean that the DPDT switch must be rated to 50amp? I have looked at mouser and future and cannot find a DC switch with such a rating. Any help is welcome!

Elias

 

Generally you use a relay that you control from the switch. Look at car relays.

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I apologise if this is rather simplistic but it may help :

A high current relay is a very useful electrical control item. The voltage across the coil winding of a relay controls the relay contact closures. When a voltage is applied to the coil of a relay a small current in the coil, a few milliamps, produces a magnetic field that causes two contacts to touch. The two contacts are not electrically connected to the coil and can operate freely in any circuit. The contacts can take amps and are the heavy duty part of the relay doing the real work of carrying current to your electrical system from the battery to your electrical circuits.
When the coil is energised you can normally hear the contacts click together and when the coil voltage is removed you can hear them click back. The contact operation time is very quick.

In order to chose your relay you have to determine :

1. The maximum current that your battery provides to your complete system.
This can be measured with a DC current meter or calculated from the total power of your system, measured in Watts. Current = Power / Battery Voltage.
The current rating of the relay contacts should be rated higher than this maximum current as if you have inductive loads, like electric motors the current at switch on could be several times the normal running current. A relay data sheet may mention this inductive situation.

2. What coil voltage you require. The coil can be connected to your battery through a low current rated switch. So the coil voltage rating will be the same as your battery voltage.

3. The cost of the relay will depend on the current rating as this will determine the size of the contacts and the overall package size.

4. If you require more contacts then the relay must be chosen carefully. Most relays will have either normally open contacts ( N/O ) that will close when the coil is energised. You can buy relays that work the other way around, the contacts are normally closed ( N/C ) and they will open when the coil is energised. Some relays have both options ( N/C + N/O ). A drawing of the contact arrangements will normally make this clear.What contact arrangement you chose depends on what type of control actions you require.

5. From a wiring point of view you will have to use heavy duty wiring to connect the contacts and the type of connection, soldered or crimp, may be important to you. The coil wiring will be thinner wire and easier to connect. Normally the thick wires are kept to a minimum length to avoid excessive voltage drops along the wire. The coil wiring is not so critical. I would put a fuse in the battery line as a safety precaution, this will protect the battery if a huge current is taken by a faulty circuit or in cases where the wiring shorts together somewhere remote from the battery.

Remember that a relay is like a power steering system on a car. A small turning force on the wheel brings much more power into the system that actually turns the wheels. In other words a small current into the relay coil brings large contacts together that switch a much larger current into your circuits.

Note that battery operated relays are sold specifically for cars where fairly large currents, up to 40A are required in various parts of the car for lights, heaters and even audio power amplifiers etc. It would be highly likely that one of these reliable relays would do the job at reasonable cost.
A good quality in-line fuse should also be available in a plastic case.

 

Sounds like a house hold circuit break (2 of them). Flip one 180 degrees and tie the switched together.

Maybe look for a 12VDC contactor and have a to switch toggle it.

 

Residential circuit breakers are rated for AC only, not DC. Switches (and breakers) rated for 50A AC would only be rated for about 5A to 10A DC. Though you can find switches rated at 25A/125vA and 25A/12VDC. The problem is not how much current they can carry, but how much current they can interupt without continuing to arc over. AC current goes to zero 60 times every second, so it helps in cutting off the current. Look for DC ratings only.

Ken

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you only need to switch one pole of the battery, not both. i recommend switching the positive pole, and connecting all the grounds together.

50A dc relay or "contactor" should be readily available at any auto parts store.

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Don't forget that your relay (more properly "contactor" since it's a "relay on steroids") must have its coil powered by the battery. If you're switching the battery over because it's dead and you're powering the contactor from that battery, you could be in trouble. You're not supposed to let a battery go completely flat, but it may happen. You can't let the contactor coil voltage be switched along with the battery (load and coil both connected to the contactor COMMON terminals) because you may end up with a high-powered buzzer.

If you have the batteries, and otherwise must switch over, it would be just as easy to wire the batteries in parallel. Same overall load life, easier switching. Just not as portable if you intend to remove the battery for charging. If they're charged while sitting in the boat, no problem. Just charge them as a parallel-connected pair.

The only problem you'd have with parallel batteries is that they must be identical or you may end up with the one that's a bit "hotter" trying to charge the other. The best scenario is to go out and buy two identical batteries at the same time. If you ever have to replace a battery with a new one, replace them both at the same time.

Dean

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Hi have a look at
http://shop.sailnet.com/product_info...4b720bb69dc018

 

eliask08, I re-read your initial thread and your enquiry was about a simple switch to change from one battery to another battery for your trolling motor. Unless you have a big boat with a big motor then usually extra batteries are re-charged on-shore. A simple permanently installed battery setup is usually trickle recharged while the motor is running from a little diode mechanism. (just like in a ride-on mower). However, this method will not replenish charge in two batteries that are running a trolling motor.
If your setup is such that you do not require "on-board" battery recharging then the simple switch as per the previous post will do the job for charged batteries. If your setup requires "on-board charging" then I suggest that you heed the other members' advice regarding relays and or contactors. There is a wealth of information available regarding dual battery setups in fourwheel drive forums.
Cheers RH

 

Hi there all!!

Have a lil something to make!! dont need it be very expensive.

Here is the deal!!

What Im trying to make is an AC powered switch using a relay that can handle relatively large switching i.e. around 10-15AMPs.

What may aim is.. that when the main supply is there (AC suplpy 220V) the relay switches the load ON.

When the main gets interrupted for like even 5-10 seconds and comes back the relay switches OFF and can only be switched on upon pressing some RESET button/switch.

When the main is OFF, pressing the RESET switch still does not switches on the Relay (ofcourse).

Appreciate in advance help from you guys! Thanks!

 

Use a latching relay, you can get relays rated for 230VAC so the mains requirement isn't a problem.

You can remove the normally closed reset button and replace it with a piece of wire. Press the trigger button, to turn it on and when the mains is disconnected and reconnected, it will disconnect the load.

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Other than simply connecting the 2 batteries together as suggested above, get 3 plugs, something like the SB50 series by Anderson. They are used very widely to connect batteries in forklifts, golf carts, marine, vehicles, etc. They are easy to install, cheap ( $5 each ) and provide years of reliable service.

Newark sells them : http://www.newark.com/96F6194/connec...-PRODUCTS-6319

or you can get them at most RV, or Marine suppliers.

 

Many thanks Hero!! i shall give it a shot!! hope it works for me..