What is this thing? (Electrical)

[Chotu]

This is from a 28 foot Grady white.

A family member got one of these boats. I have been helping them go through the wiring a bit.

this is connected to the battery switch on one side, and to the starting battery on the other side. On the side of it it talks about protected connections. As if it is some sort of fuse.

However, it kind of has to be an echo charger or battery isolator, right?

is anyone familiar with this exact model? I don’t seem to be finding any markings or numbers on it. Just a sticker on one side that talks about the protected circuits.

[Singularity]

Looks like a battery isolator.

<3 minute video from eMarine on testing a battery isolator: https://youtu.be/oqCUyJ2P3yI

[s/v Jedi]

Where it says “circuit protection” it shows the symbol for a fuse. You are supposed to install fuses there.

Yes, it is an isolator… I would guess it’s diode based so high loss. Victron ArgoFET is the modern version of it with minimum losses.

[Chotu]

Thank you!

I will test it to make sure it's functioning properly.

Ahhhhh. Makes sense about the circuit protection diagram.

[stormalong]

Yes, it is an isolator but the way it is installed serves no useful purpose. The idea is to be able to charge two batteries from one alternator. Without a second battery all it does is create a voltage drop which undercharges the battery. If the alternator is externally regulated with a voltage sense at the battery it will work OK but it is pointless. On an internally regulated alternator the voltage to the battery is about .6 volts less than the alternator is producing. Consistently undercharging the battery and shortening it's life.

[smac999]

It’s either a battery isolator. Although very uncommon on out boards.

Or the opposite, a dual power source isolator. To power critical things from 2 different sources. I see them on engine controls or steering pumps from both engine batteries.

But with only 2 wires. It’s not doing either of those things. Not correctly anyways

Edit I looked at the full size pic and it’s clearly a battery isolator. But with only 2 wires it’s hooked up wrong. It may be constantly taking power from one battery to the other. I have seen that before..,

[Chotu]

precisely.

this is part of the investigation. For some reason, unknown to me, there are voltage readings on several of the electronics items.

There is a Garman GPS that reads the voltage. There is a humming bird radar system which also reads the voltage.

then there is the standard voltmeter in the instrument cluster.

when they bought this boat very recently, their first boat, the seller told him don’t worry about the fact that these things all read different voltages.

Red flag. Lol

so I am looking through things to try to investigate a little bit. This little piece might be part of the problem I’m thinking. And yes. I noticed it’s not installed properly.

where it sits is between the 1/2/All battery switch and the starter battery. Does that make any sense?

The house bank is connected to the switch directly and the starter battery is connected to the switch with this isolator, wired just like that, sitting between them.

The idea must be to preserve the starter battery when you run the house back down. But, it doesn’t really make any sense. Because I can switch to the starter battery or the house bank and run everything from either one. Using the battery switch. If I turn it to off everything shuts off.

so if it were preventing a drain from the starter battery, all of that stuff shouldn’t work when I select the starter battery as the source of power.

thinking about it the other way around, maybe it’s trying to do something with the charging. But I don’t see what.

It’s not set up in a way that I am familiar with.

[Chotu]

It seems to be set up something like this diagram.

[Chotu]

But the battery switch makes it really confusing. On pole #1, the battery switch is connected to a positive bus bar, and both house batteries. One cable from each of those items goes to pole #1. Three cables and terminals are ganged on pole #1.

On pole #2, the battery switch is connected to the starting battery with this isolator in between, wired as shown.

On pole #3, the battery switch is connected to the starter motor. My head hurts. Hahaha

The battery switch takes pole #3 (the starter) and connects either pole #1 or pole #2… , or “all” which is pole #1 and pole #2 at the same time. To the starter!

[rslifkin]

Originally Posted by Chotu

There is a Garman GPS that reads the voltage. There is a humming bird radar system which also reads the voltage.

then there is the standard voltmeter in the instrument cluster.

when they bought this boat very recently, their first boat, the seller told him don’t worry about the fact that these things all read different voltages.

That may or may not be a concern. I've seen a few chartplotters, etc. that read lower than actual voltage due to voltage drop in the provided wiring pigtail and/or inaccuracy in the internal measurement. So I wouldn't rely on that as a good/bad thing.

[Rumrace]

It’s a Zeener I think. Most Grandy’s have a big alt on one motor and the power steering rack on the other. At 3500-4400 the motor(s) may produce more power than the batteries need the zeener prevents excess juice from destroying the alt. They have been around pre alternators we’re pretty common in the 50’s on motorcycles with a generator and magneto. On the front neck of a triumph Ducati etc you’ll see a tiny finned piece with a single wire to it. Zeener Diode.
That’s my guess. That said there are dozens of folks imitating the Mercathode and merc knows better than suing China for patent infringement. The ground where the imitations or the original will have 3 plastic layers and suffer really bad wire corrosion.
Made mostly for Fords and they work really well. Mercathode was a dealer option on any Mercruiser inboard driveline package. Protects the driveline

[Chotu]

Yeah. This is a single engine MerCruiser. V8.

I probably should have mentioned that.

[rslifkin]

Originally Posted by Rumrace

It’s a Zeener I think. Most Grandy’s have a big alt on one motor and the power steering rack on the other. At 3500-4400 the motor(s) may produce more power than the batteries need the zeener prevents excess juice from destroying the alt.

Modern alternators are regulated and there's no need to dump excess power, etc. As long as the output isn't totally disconnected, it's a non-issue. So I highly doubt that's what this is.

[Chotu]

Originally Posted by rslifkin

Modern alternators are regulated and there's no need to dump excess power, etc. As long as the output isn't totally disconnected, it's a non-issue. So I highly doubt that's what this is.

The thing certainly is a mystery. At least how it is wired. The battery switch seems to be dealing with where the starter is obtaining its power.

It’s also a bit of a mess because I haven’t been able to exactly trace where the electronic components are getting their power. They do turn off when the battery switch is in the off position.

But there are a lot of wires connected directly to the batteries. I guess I’ll have to keep working through it and show him how to systematically and slowly figure it all out.

[Chotu]

I worked up a drawing. A schematic. This is the wiring.