Ground on LifePO4 house bank

[Tia Bu]

If I keep my lead acid starter battery and keep it connected to the engine as it currently is, and if I then use a DC to DC charger between the starter battery and the new LifePO4 house bank, does the negative bus of the house bank need to be connected to the engine block?

The house bank would also be charged directly via solar panels and an AC battery charger.

[Tia Bu]

I'm bumping this to see if I can get an answer.

[Cheyne]

I have a single primary ground that is connected to my Port engine. My starter battery connects directly to the engine. My house bank connects to that engine via a bus bar inside the electrical room. This is they way we set it up about 5 years ago when I was working with a friend who is a marine electrician. We recently connected the starboard engine ground to the port ground also.

Cheyne

[wholybee]

Yes, all grounds connect together. The house battery could connect to the engine, or it could connect to a negative bus bar for the the start battery, or directly to the start battery negative.

What is important is that it only happens at one place, so there is only one path from one battery to the other. The path should also be short and low resistance, because your charge current will go through this path.

[GordMay]

“DC Negative & Grounding Diagram”
➥ https://www.cruisersforum.com/galler...r&imageuser=79

[Tia Bu]

Originally Posted by wholybee

Yes, all grounds connect together. The house battery could connect to the engine, or it could connect to a negative bus bar for the the start battery, or directly to the start battery negative.

What is important is that it only happens at one place, so there is only one path from one battery to the other. The path should also be short and low resistance, because your charge current will go through this path.

Thanks, but I don't understand what you say about the charge current. Each charge source has a negative in and negative out. The house bank would charge from solar, an AC to DC charger, and the DC to DC charger. The starter battery would charge only from the alternator. The two banks are of two different chemistries (lead acid and Life PO4,) and I thought the two banks were never to be connected?

[newhaul]

Originally Posted by Tia Bu

Thanks, but I don't understand what you say about the charge current. Each charge source has a negative in and negative out. The house bank would charge from solar, an AC to DC charger, and the DC to DC charger. The starter battery would charge only from the alternator. The two banks are of two different chemistries (lead acid and Life PO4,) and I thought the two banks were never to be connected?

All grounds should eventually end up at a hull zinc grounding plate. .

[Tia Bu]

Originally Posted by newhaul

All grounds should eventually end up at a hull zinc grounding plate. .

Is it ok to ask why?

[newhaul]

Originally Posted by Tia Bu

Is it ok to ask why?

Corrosion protection and protect from lightening strike damage

[wholybee]

Originally Posted by Tia Bu

Thanks, but I don't understand what you say about the charge current. Each charge source has a negative in and negative out. The house bank would charge from solar, an AC to DC charger, and the DC to DC charger. The starter battery would charge only from the alternator. The two banks are of two different chemistries (lead acid and Life PO4,) and I thought the two banks were never to be connected?

A DCDC normally only has the positive in and out, and a single ground. So, the current for charging from battery to battery would flow through the negative path between them.

There are very few reasons to isolate the grounds on multiple banks. And unless you have a reason and can articulate why, you should not isolate them. Connecting all the negative terminals together is not the same as connecting two batteries together. It is perfectly fine and the normal practice, even with different chemistries.

[CarlF]

As long as there’s no positive cable connection between the two banks no current will flow between the banks even if they share a common ground.

[newhaul]

Originally Posted by wholybee

A DCDC normally only has the positive in and out, and a single ground. So, the current for charging from battery to battery would flow through the negative path between them.

There are very few reasons to isolate the grounds on multiple banks. And unless you have a reason and can articulate why, you should not isolate them. Connecting all the negative terminals together is not the same as connecting two batteries together. It is perfectly fine and the normal practice, even with different chemistries.

Not correct .
My renogy 40amp dc2dc has both positive and negative in and out on it .total isolating the batteries at that point.
Why I don't know considering all of my grounding connections are on a common busbar

Victron has both in and out as well it appears

[Tia Bu]

Originally Posted by newhaul

Not correct .
My renogy 40amp dc2dc has both positive and negative in and out on it .total isolating the batteries at that point.
Why I don't know considering all of my grounding connections are on a common busbar

Victron has both in and out as well it appears

Which is what I noticed. Why? What's the right answer?

[Tia Bu]

I'm going to bump this one more time:

Should the grounds on the lithium house bank and the lead acid starter battery be connected or not? Real world experience? Reference to an authoritative source?

Thanks to everyone for their help so far.

[newhaul]

Originally Posted by Tia Bu

I'm going to bump this one more time:

Should the grounds on the lithium house bank and the lead acid starter battery be connected or not? Real world experience? Reference to an authoritative source?

Thanks to everyone for their help so far.

I will say it one more time
ALL grounds are eventually connected to a single hull grounding plate.
Again
ALL grounds are eventually connected to a single hull grounding plate.