Shore power inlet for battery charger

Zonker

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Schottky diodes have less voltage drop (~0.2V?) than regular ones. But lead-acid batteries are still sensitive to voltage levels so even 0.2V matters.

 

weightless

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Schottky diodes have less voltage drop (~0.2V?) than regular ones. But lead-acid batteries are still sensitive to voltage levels so even 0.2V matters.
Yeah and the alleged "point" was to block ~1 V as with a isolator... Putting that block on a wire that's supposed to carry current is starting to seem problematic.

 

Rain Man

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Galvanic isolaters have to be fail-safe now.  That means the ground has to be kept connected even if the isolator fails. 

Fail-safe ones are expensive.  Isolation transformers are even more expensive. A cheaper/better solution would be a solar panel on an isolated ground to keep the battery charged and just run the heater/dehumidifier off the power cord.

 
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weightless

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Another cheapish option might be to try a charger with a two prong plug. I think it's SOP to connect the DC negative to ground on chargers that have a ground and I wouldn't be surprised if that was where the problem is here. Presumably they don't connect DC to ground if they don't have ground.

 
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See Level

Working to overcome my inner peace
Put an amp clamp on the cord and see if it registers above 0, if it does try unplugging things until it doesn't.

Rental shops have them if you don't.

 
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weightless

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weightless

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How does the battery or the charger know it's on shore?
Their attempts to burn up the saildrive are frustrated?

I wonder if "marine" battery chargers have better isolation. Maybe they don't directly connect the earth pin to the battery negative?

 
I am following this topic closely. I have a 30-foot racer and want to install a simple shore power system. The only 120v load I have on board is a Blue Sea Systems 15A battery charger to charge the Lifeline AGM starting battery and a secondary bank used occasionally for distance events. The boat has an inboard. In the past I have always just dropped a cord into the boat through a deck plate in the cockpit cubby. I installed a plug like this, but it hasn't been connected to anything at the moment. I think the big knock on this kind of plug is no strain relief, no means to retain/lock the cord in the plug, so a moving boat on a dock poses failures points for this type of device.

I have most of what I need as far as components but no isolation transformer or galvanic isolator. As I understand it a galvanic isolator may be used as long as it is the failsafe type.

150BBIW_HR.jpg

 
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El Borracho

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I am following this topic closely. I have a 30-foot racer and want to install a simple shore power system. The only 120v load I have on board is a Blue Sea Systems 15A battery charger ...
Resist. Don't do it. Slippery slope. You can see it already: Isolators, corrosion, weight, and the cost. Power cord has none of those issues. Plus such "convenience" attracts all manner of appliances better suited to a condo than a racer.

 
El Bo:

OK sure I don't disagree especially about adding complication, components and weight to the boat - but doesn't the boat have the same (potential) galvanic issues with a dropped in cord than with rudimentary shore power built in? If not, why not?

 
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Rain Man

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El Bo:

OK sure I don't disagree especially about adding complication, components and weight to the boat - but doesn't the boat have the same (potential) galvanic issues with a dropped in cord than with rudimentary shore power built in? If not, why not?
Only if the ground of the dropped in power cord is connected to the ground of the DC system, allowing galvanic and other currents to leak into the water if the DC system ground is connected to underwater metal such as the prop shaft and prop.

The issue is battery chargers run by shore power - because that is the device that often connects shore power ground to DC ground.  Personally, I wouldn't use one if at all possible.  What happens, though, is people want to run things on their boat while it is at the dock such as bilge pumps, so they want to keep their batteries charged. 

A solution is to keep the battery charged with a solar panel, and run everything else (heater, dehumidifier) from a dropped in power cord.  

Good description of isolation transformer operation here: https://www.victronenergy.com/upload/documents/Datasheet-Isolation-Transformers-EN.pdf   Note that the small one (2000W) weighs 10 kg.

Disclosure:  I have a cruising boat with a Xantrex charger.   I had to install a galvanic isolator as the zincs were disappearing rapidly at the dock.  I was lucky and found a brand new failsafe one on-line for $200 - otherwise a new one would have been $500.  It might not solve the problem because galvanic currents are just one possible issue.  If I find the galvanic isolator doesn't solve the problem, I will switch back to a dropped-in power cord - isolation transformers are crazy expensive and heavy - and just keep my solar panel running year-round. 

 
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El Borracho

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El Bo:

OK sure I don't disagree especially about adding complication components and weight to the boat - but won't the boat have the same (potential) galvanic issues with a dropped in cord than with a rudimentary shore power built in? If not, why not?
What @Rain Man ^^^ wrote. Get a solar charger. Can be small. I have a 50' full-on cruising boat with zero shore power capability. If I need to use a power tool, or a heater on a cold night, or charge a flat battery (rare), I temporarily lead the power cord in from where it lives in the dock box. When not cruising, like the present, just a small solar panel suffices. It is even in the shade much of the time.

 
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Quickstep192

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What @Rain Man ^^^ wrote. Get a solar charger. Can be small. I have a 50' full-on cruising boat with zero shore power capability. If I need to use a power tool, or a heater on a cold night, or charge a flat battery (rare), I temporarily lead the power cord in from where it lives in the dock box. When not cruising, like the present, just a small solar panel suffices. It is even in the shade much of the time.


What @Rain Man ^^^ wrote. Get a solar charger. Can be small. I have a 50' full-on cruising boat with zero shore power capability. If I need to use a power tool, or a heater on a cold night, or charge a flat battery (rare), I temporarily lead the power cord in from where it lives in the dock box. When not cruising, like the present, just a small solar panel suffices. It is even in the shade much of the time.
I’m loving this idea. Can you recommend a solar charger? 

 

El Borracho

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I’m loving this idea. Can you recommend a solar charger? 
Sorry, no. As I am a long range cruiser I have a much larger solar capability. Most of it stowed while languishing at the marina. Plus I’m not overly impressed with the Blue Seas MPPT regulator that I have.

I’d get something popular from Defender. For you, something easy to carry or stow. Make some effort to provide a quick, easy, safe way to connect it to the battery electrical system. Size depends on how much you regularly need to bring the batteries back up after a typical race. Best to recharge in a day or two. I’d err on the small side. If is apt to be left connected for a long time make sure it is quality enough, configurable, not to cook the batteries. 

 

Quickstep192

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Chesapeake
I'm mostly interested in keeping the batteries toped up during the winter and during periods of non-use. The boat is kept on a lift at my house, so I'm pretty much able to do anything I'd like. The one restriction that I do have is that there's not enough room for an extension cord to pass between my drop board and hatch cover. Bringing in an extension cord anywhere else would let rain in.  

I think or hope that keeping the boat out of the water should help avoid any galvanic issues. 

 

Rain Man

Super Anarchist
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Wet coast.
I'm mostly interested in keeping the batteries toped up during the winter and during periods of non-use. The boat is kept on a lift at my house, so I'm pretty much able to do anything I'd like. The one restriction that I do have is that there's not enough room for an extension cord to pass between my drop board and hatch cover. Bringing in an extension cord anywhere else would let rain in.  

I think or hope that keeping the boat out of the water should help avoid any galvanic issues. 
For less than $200 USD you can get a 100W flexible panel from Renogy and a 10A programmable controller.  A bit of wiring later and you have a charging system that you can use over the winter to keep things topped up.  Then you also have something to use if you cruise or go offshore racing.  

The biggest problem is figuring out how to get the solar panel DC cables into the boat neatly.  There are some nice deck glands out there but you might have an existing entry port you can use.

IMHO thus is a better investment than an isolator or transformer for your application.

 

Zonker

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The one restriction that I do have is that there's not enough room for an extension cord to pass between my drop board and hatch cover.
You drill a 3/8" diameter hole in the drop board very close to the top edge. Then saw down to the hole and remove the bit of wood or plastic...

This secret technique is what we in the industry call "a notch". I only offer this because I'm a nice guy. Don't spread this sort of secret around.

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