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  #1  
Old 12-16-2011
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Question Radio battery backup

I'd like to wire in a gell battery between my battery bank and VHS. So I can be garanteed of power to the radio if I drop a cell in my battery bank. Does anyone know how to do this????
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Old 12-16-2011
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A gellcell demands a different charge regime than a normal battery. That means yo will need a seperate charger for this battery. Although blocking diodes or relays might be used, it is best to double the boats battey voltage and use this as a source to charge the battery for your radio. You will need a voltage doubler and a charger for this unit.
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Old 12-16-2011
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Presuming you have both a house bank and a start battery, you could install an A/B switch to power the radio off the start battery in the event of a house failure.

A good handheld and external antenna might be a good idea and a similar investment to an additional battery and charger.
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Last edited by Minnewaska; 12-16-2011 at 06:04 AM.
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Old 12-16-2011
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I keep a 12V motor bike battery with hard wired wire and clips for reserve for this purpose and/or if needed in life raft for handheld/mobile/gps etc
I thought it was a smart idea.

Is this Rockhampton. QLD?
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Last edited by St Anna; 12-16-2011 at 06:46 AM.
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Old 12-16-2011
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Quote:
Originally Posted by Minnewaska View Post
Presuming you have both a house bank and a start battery, you could install an A/B switch to power the radio off the start battery in the event of a house failure.

A good handheld and external antenna might be a good idea and a similar investment to an additional battery and charger.
There are adapters that would allow you to plug the handheld into the mast antenna. I don't know how much power would be lost from a 5w handheld going up 30' or more of coax, but that info can be found online.
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Fastbackfill,

It's pretty simple to do what you originally asked.

All you need do is install a single-pole-double-throw (SPDT) switch to switch the positive power lead from your VHF between the house batteries (normal position) and the new emergency battery.

A VHF radio draws about 5-8 amps maximum, so the switch needs to be capable of handling that amperage @ 12 volts DC. Appropriate heavy duty switches would be like: Cole Hersee Co. 5584 or 5586 SPDT On-On or On-Off-On Toggle Switches.

First, ensure that the negative pole on the new battery is connected to the boat's negative ground.

Now, carefully remove the radio's positive (red) power lead from the existing switch or breaker and attach it to the center pole of the SPDT switch. Then, run a new AWG10 or 12 wire from one of the end poles on that switch to the original switch or breaker.

Test that out. Your radio should work as before with the new SPDT switch thrown one way or the other.

Now, simply attach the positive pole of the new battery to the other end of the SPDT switch, using a new AWG10 or 12 wire.

It would be good to include a 10A fuse in that wire, located close to the battery.

That's all that's needed to wire in a spare battery (emergency power source).

HOWEVER, now you have to find a way to keep the new battery charged. How you solve this will depend on how your boat is set up at present and what type/size of spare battery you use. Also will depend on the type of sailing you do. If you just do weekend sailing or short trips, you could charge the spare battery from shore power using a small smart charger. If it's a gel, you'll need a charger capable of charging gelled batteries. Gels have a very low self-discharge rate, so you wouldn't have to worry about charging it on a short cruise.

Bill

Last edited by btrayfors; 12-16-2011 at 07:05 PM.
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I have mounted a small emergency Gel battery on my boat. The main advantage is can be mounted high up so if the boat is flooded it will still work.
Charging is easy. It has low self discharge, but when the voltage is appropriate, such as when my solar regulator is on float, I Occasionally switch it on to charge. My battery monitor shows how much current its taking so I get a good idea of the state of charge.
Very inexpensive if you fit it yourself and could prove to be useful.

Mine is also wired up to run the anchor lights and gps. If there is lightning about I can disconnect most of the electrics and just run these vital systems. It would not help in a large direct strike, but I had an strike a few years ago and all the equipment that was off survived.
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Why not just install the SPDT switch from the house to the start batt. The later should already have a charger or simply needs the engine on to keep the radio operative for a lengthy period. Presumably, once back to shore, you would fix the house bank.
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Old 12-16-2011
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Quote:
Originally Posted by St Anna View Post
I keep a 12V motor bike battery with hard wired wire and clips for reserve for this purpose and/or if needed in life raft for handheld/mobile/gps etc
I thought it was a smart idea.

Is this Rockhampton. QLD?
Another option is a booster battery.

When I do deliveries and the condition of the boats batteries is unknown which it often is I often will bring my booster.
Has handle, comes with clamps and is easily charged with 110.
The booster is versatile. It will start the engine, run the radio or lights or GPS.
I also bring a hand held VHS.

Of course if I have to take the train home I take my chances.

I really don't like the idea of complicating the boats electric system for a low probability issue. At some point the solution might cause more risk and more points of failure than the risk of the original event.
An independent, portable versatile solution like the booster as almost no downside.

Last edited by davidpm; 12-16-2011 at 07:33 PM.
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All passenger carrying vessels (Can) require this set up. I use a small lead acid snowmobile or similar. Same as all the other batteries on board and all charge together from all sources .Starter bat isolates when key turns off and radio bat is isolated by a designated regulator in line.from house.When the house bats discharge the radio is still good for days and the GPS,also on that line,shows the voltage . Another advantage is that it isolates the lap top from voltage drop/ surges when heavy draw would other wise kick it off line. Works for me.
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