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first sailed january 2008
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1,409 Posts
Discussion Starter · #1 ·
It turns out the plug I have on my boat only works when I am connected to shore power, so I got a small 400 watt inverter with two battery clamps.

I have been using it to charge things and removing it from the battery when not in use. I attach the red clamp to the battery post and them the black clamp to the negative battery post. The black clamp produced sparks. It doesn't feel safe.

Is this ok? It does have an on off switch, should I just attach it permanently near my batteries or attach the black clamp to something else or...just not worry about it? I'm doubting we are going to go for the just not worry about it plan.

Thanks for your help.
 

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One of None
Hunter 34
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8,642 Posts
It makes little sparks? Meaning it's always on like a TV set?
 

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One of None
Hunter 34
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8,642 Posts
does it have an led pilot light in/on the switch?
 

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76 Posts
Sparks even when the switch is off (obviously) show current passing even when the switch is off. Do you have a multimeter? You could check the resistance between the red and black battery clamps with the switch off.
 

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Inverters do pass current when the final DC wire is put in place - it is normal. It is also mentioned in the install manuals of many inverters to expect this.

A proper install of a larger inverter includes a switch in the DC positive wire - as well as adequate fusing. This can certainly be done in the cast of a small inverter as well. If the switch is off when the wires are connected there is no spark.
 

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Mermaid Hunter
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5,686 Posts
Is this ok?
No.

Remember that when charging batteries vent hydrogen and water. Add sparks and you have a fuel, an oxidizer, and a source of ignition. THAT is why ABYC and others have so many recommendations for battery boxes, switches, and connections.

In addition to the sparking be aware that battery spring clamps do not make terribly good connections so there will be a voltage drop and heat.

I suggest you permanently connect fused and switched cables to the inverter. If you want to make the inverter portable use good quality connectors like Anderson Powerpoles or Powerlet connectors. For a 400W inverter I'd size wires and connectors for 40A and fuse for 30A or 35A. Make sure the inverter is well-ventilated wherever you put it.
 

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If you are just charging phones, tablets, etc. consider getting a suitable 12V charger. Much more efficient, especially since you are probably using only a small percentage of the 400w capacity of your inverter.
 

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I suggest you permanently connect fused and switched cables to the inverter. If you want to make the inverter portable use good quality connectors like Anderson Powerpoles or Powerlet connectors. For a 400W inverter I'd size wires and connectors for 40A and fuse for 30A or 35A. Make sure the inverter is well-ventilated wherever you put it.
Fuse for wire size. A fuse of 40 amps or less may have nuisance blows.
 

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69' Coronado 25
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323 Posts
If you are just charging phones, tablets, etc. consider getting a suitable 12V charger. Much more efficient, especially since you are probably using only a small percentage of the 400w capacity of your inverter.
That's what I did, I added 12v sockets at the dinette, galley area and v-berth. I want to install a weather proof one in the cockpit.
 

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Mermaid Hunter
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Fuse for wire size. A fuse of 40 amps or less may have nuisance blows.
Design for the system. Set the fuse for some margin above expected loads (taking fast-blow and slow-blow into account). Size the wires and connectors for margin above that.

If the fuse is right at the wire sizing than manufacturing anomalies could make the wire the weakest link, which is bad. The fuse should always blow before the wire melts.
 

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first sailed january 2008
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1,409 Posts
Discussion Starter · #15 ·
Do gel batteries still emit gasses?

Do these inverters not have a fuse already in them that they shut themselves off if overloaded?

I like the idea about cutting of the big clamps and crimping on smaller rings to more permanently attach to the smaller battery posts like how the wires from my engine are.
 

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██▓▓▒▒░&
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Lots of 12v equipment is actually "on" even when it is off. Think about your home TV set, cable box, other devices. They're vampires, always on. A lot of mobile radios are "on" even when they are off as well--and you'd think that when you turned the power switch off, there would be no reason for that. Nope, the engineers are smarter than we are. (ahuh.)

So I wouldn't find the sparking to be abnormal or unusual. Anything that attaches with clips is only meant to be attached when being used.

Whether the sparks could be a problem...only if there are explosive gasses and hopefully your battery is vented well enough for that not to be a problem. If you want to worry, you'd probably want a "marine grade" inverter that was also certified explosion-proof and non-sparking, permanently installed. And probably 10x the price.

You can install a simple inexpensive on-off SPST power switch in one of those power cords if you want, so you can leave the clip attached to the battery and just turn it on afterwards. There will be no spark at the post BUT there's still usually an invisible spark inside when you turn on a switch, unless you go to the sealed explosion-proof ones. That you probably won't find a the local stores, and don't want to buy from China via online.
 

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Mermaid Hunter
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Do gel batteries still emit gasses?
Yes, although less and only at the end of the charging cycle (or if overcharged). That's why there are pressure vents.

Do these inverters not have a fuse already in them that they shut themselves off if overloaded?
Even if they do, what protects the wires? Fuse as close to the source as possible. I really like Blue Seas terminal fuses for that very reason.
 

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first sailed january 2008
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1,409 Posts
Discussion Starter · #18 ·
Thank you both for all the info, and for remembering in boycotting china! lol. Cool people on here.

Does the fact that I have to blue sea fused that say 30 on them next to my battery switch count for anything or will I be bypassing those by connecting directly to the battery?

So I can actually cut these red and black wires and splice ring terminals to them and thy will work? I just can't get over the fact that you can cut wires. You would think sometimes the splicing wouldn't work.

I've got this dialectric silicone compound. I'm putting it on all my splices. Good, no?
 

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Mermaid Hunter
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5,686 Posts
Does the fact that I have to blue sea fused that say 30 on them next to my battery switch count for anything or will I be bypassing those by connecting directly to the battery?
It sounds like you are bypassing them.

So I can actually cut these red and black wires and splice ring terminals to them and thy will work? I just can't get over the fact that you can cut wires. You would think sometimes the splicing wouldn't work.
Go ahead. Read MaineSail's articles on crimping.

I've got this dialectric silicone compound. I'm putting it on all my splices. Good, no?
No. A good splice is cold welded. Don't confuse the issue with insulating material. Look up dielectric on Wikipedia.
 
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