Stepdown Converter ACC?

[coldfish]

I converted my boat to electric and have a nice 72v 100ah LifePo4 battery. I still have the old 12v system set up, but it's a bit heavy (2 agm deep cycle marine) and honestly unnecessary. I'm going to replace them with a smaller, lighter 12v LifePo4 that will be really just for 2 of the bilge pumps and some smaller things that need to be on all the time.

Moreover, I put in an electric toilet in the bow, and as my daughter found out, it really needs ALL that 12v power.

I bought a stepdown converter (Cllena DC 40V-90V to 12V Converter Voltage Regulator Reducer 48V 60V 72V Step Down to 12V 40A 360W Converter) and I'm going to run a 72v line to the forward electrical cabinet and use that for power.

The problem is that I've heard some horror stories about battery drains and fires, etc... And I realized that this particular converter has an ACC input, so the converter doesn't actually do anything until that input gets power.

If you just want it on all the time, then you can put a jumper on it and the main power will be attached to it and you get it all the time.

So, here's the problem/question: I have a 72v line going to the bow already. It's on the starboard side and the pilot console in the galley is on the port side. I would like a toggle switch on the console to energize the stepdown.

Now, that seems like no big deal, but right now I have a bunch of toggles that are running from the console on a multi-core line to a set of relays that turn on nav lights, bunk lights, office lights, cameras, wifi, etc... But, the relays are switched with tiny little 18awg wires at 12v. Now, on a relay, I could have as little as 5v positive hit it and that would be enough to kick it over. I'm just wondering if I could just use a regular 12v wire like I do with all the relays to put it in ACC mode, or is that going to blow everything up.

My alternative is to run a single 72v line from the batter, to the console toggle switch, and then to the acc on the stepdown converter. And I'd like to avoid yet another wire. I really like one fat line running from the console to the bow and one from the console to the stern.

Does anyone know anything about this?

note: I know some people will say that I need to have a ground back to the 12v battery. I actually do that with the relays, but the stepdown doesn't have an alternate ground for the acc. However, using that massive 72v battery's ground for the amount of electricity coming via an acc should be negligible.

[Statistical]

Do you have a link to manual for the converter?

As for the relay (remote on/off ssitch) yes the wiring can be small and in most cases can/is lower voltage. Exactly what is allowed should be spelled out in the manual.

As for the negative there should be no such thing as 72V negative and 12V negative. There should just be DC negative and everything requiring a negative connection goes there. That is important for safety because othewise you can end up with floating negative and different negative wires at different voltage relative to ground. Even if you have seperate 72V - and 12V - busbars for orgnization they should be tied together.

[SailingHarmonie]

Not wanting to hijack your question thread here, but.. I guess I am...

I am curious, what additional safety measures do you add to a 72V DC system that is distributed around the boat? My understanding is that anything above 50V is normally considered to be potentially lethal and falls outside the usual recommendations for small boat DC wiring.

[Statistical]

Originally Posted by SailingHarmonie

Not wanting to hijack your question thread here, but.. I guess I am...

I am curious, what additional safety measures do you add to a 72V DC system that is distributed around the boat? My understanding is that anything above 50V is normally considered to be potentially lethal and falls outside the usual recommendations for small boat DC wiring.

ABYC has some requirement in E-30 "Electric Propulsion" for those who follow ABYC or are looking for best practices. It involves some extra stuff beyond E-11 but none of it seems esoteric. They require DC voltages >60V nominal to have orange markings and indicate voltage level. Battery and other primary disconnects must have a means to lock them in the open configuration. Battery and other >60VDC connectors must have covers to ensure they can't be touched. DC to DC converters between >60VDC system and <60VDC systems (like house 12/24 loads) need to be isolated. Electric propulsion >60VDC must have emergency shutoff.

I think the biggest real world challenge is finding stuff like switches. Not all marine switches even support 48VDC and even fewer support 72VDC.

[coldfish]

Originally Posted by Statistical

Do you have a link to manual for the converter?

As for the relay (remote on/off ssitch) yes the wiring can be small and in most cases can/is lower voltage. Exactly what is allowed should be spelled out in the manual.

As for the negative there should be no such thing as 72V negative and 12V negative. There should just be DC negative and everything requiring a negative connection goes there. That is important for safety because othewise you can end up with floating negative and different negative wires at different voltage relative to ground. Even if you have seperate 72V - and 12V - busbars for orgnization they should be tied together.

This is the converter: https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

I finally found some information on it and it seems that the accessory is 12v and is normally connected to the ignition on a car/rv, so the 12v switch will be perfectly to spec.

which is awesome, since I don't feel like running more wires!

[coldfish]

Originally Posted by Statistical

ABYC has some requirement in E-30 "Electric Propulsion" for those who follow ABYC or are looking for best practices. It involves some extra stuff beyond E-11 but none of it seems esoteric. They require DC voltages >60V nominal to have orange markings and indicate voltage level. Battery and other primary disconnects must have a means to lock them in the open configuration. Battery and other >60VDC connectors must have covers to ensure they can't be touched. DC to DC converters between >60VDC system and <60VDC systems (like house 12/24 loads) need to be isolated. Electric propulsion >60VDC must have emergency shutoff.

I think the biggest real world challenge is finding stuff like switches. Not all marine switches even support 48VDC and even fewer support 72VDC.

Luckily, the 72v system is really from the battery to the controller to the motor. And it's got a solenoid and emergency cut-off and a fat fuse as well. (and they're like 2 feet from each other.

The line I'm running to the forward electrical compartment is the only line out and it just goes to the stepdown. And trust me, that line is going to have a tone of "DO NOT TOUCH" tags on it!

[Statistical]

coldfish,

Actually I am going to correct my prior post regarding grounds.

ABYC says this

30.8 GROUNDING
30.8.1 The boat’s propulsion electrical system (e.g., batteries, generators, inverters) shall remain isolated from the boat’s grounding system.

30.8.2 Exposed, noncurrent carrying conductive parts of the propulsion system (e.g., motor case) shall be connected to the boat’s grounding system per ABYC E-11, AC and DC Electrical Systems on Boats.

That is different from DC voltages of 60 VDC nominal or less. So the "high voltage" (not really high medium voltage?) system should be completely isolated to include 72V neg which it sounds like that you were already doing before I steered you wrong.

[Statistical]

Originally Posted by coldfish

This is the converter: https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

I finally found some information on it and it seems that the accessory is 12v and is normally connected to the ignition on a car/rv, so the 12v switch will be perfectly to spec.

which is awesome, since I don't feel like running more wires!

Sounds good. One question I have is don't you already have a 12VDC distribution panel. Why not wire this into the input of that and provide 12 to all 12V loads. How are you powering other 12V loads?

Also be aware if the amazon listing is correct this converter is not isolated
"1. 100% full power and stable current output, non-isolated module"

You may wish to consider an isolated model. This is unfortonately more than double the cost but meanwell is a solid company and there is isolation between the 12V and 72V sides.

https://www.google.com/search?q=RSD-...hrome&ie=UTF-8

[coldfish]

Originally Posted by Statistical

Sounds good. One question I have is don't you already have a 12VDC distribution panel. Why not wire this into the input of that and provide 12 to all 12V loads. How are you powering other 12V loads?

Also be aware if the amazon listing is correct this converter is not isolated
"1. 100% full power and stable current output, non-isolated module"

You may wish to consider an isolated model. This is unfortonately more than double the cost but meanwell is a solid company and there is isolation between the 12V and 72V sides.

https://www.google.com/search?q=RSD-...hrome&ie=UTF-8

The boat actually doesn't have a real distribution panel. It's 1968 Alden Pilothouse, and it's been through a LOT. wires everywhere, little fuse boxes here and there. I literally replaced a light and even though the main power was off for that area, the light has power .... I have no idea how! Hunting through painted over bundles of wires tied up every 6inches with twine has been an exercise in futility .

Which is why I'm slowly just rewiring it.

Some new appliances that didn't exist in 1968 also needed power. Electric head, water pump, fridge, microwave, wifi, cameras, deck lights, stereo, etc.... So, it's been a lot of pulling a panel up and cringing.