Engine battery need to be connected to house ground?

[mrybas]

The alternator only charges the start battery. There are no other charge sources connected to the start battery. Do the house battery bank and start battery need to be ground together?

[smac999]

Yes it does

[mrybas]

Originally Posted by smac999

Yes it does

Can you explain why?

[hellosailor]

I would argue that they don't NEED to be. And, that "ground" is a poorly chosen and arguably misused word in the marine environment as well.

The starting battery NEEDS to be "grounded" to the engine block, or else directly to the starter and alternator in any case. The house bank does not need to be connected to the engine or the starter at all. It does not need to be connected to the starter battery at all. But it will make life more complicated if it is not connected to the alternator positive and ground, which is normally going to mean it is sharing a ground point with the starter battery.

Anyone who doesn't grasp that, really should get and read a couple of the inexpensive and well-recommended books on basic boat wiring and electrical systems, because not knowing about the basics can wind up costing you very dearly when something goes wrong. Firing questions on web forums will not get the comprehensive systems approach that the books have.

[pcmm]

Originally Posted by mrybas

The alternator only charges the start battery. There are no other charge sources connected to the start battery. Do the house battery bank and start battery need to be ground together?

If you ever need to start using the house battery, its negative will need to be connected to the engine also. The end result is that both are connected to the same ground point. Also if you ever want to charge the house bank using the engine alternator, the house bank and start bank will need both their negtives connected to the engine.

so in a round-a-bout the answer is YES

But if under no circumstances ever will the engine charge the house bank, then "Technically" the starter battery could be completely isolated from the house with no common ground.

[mrybas]

Originally Posted by pcmm

If you ever need to start using the house battery, its negative will need to be connected to the engine also. The end result is that both are connected to the same ground point. Also if you ever want to charge the house bank using the engine alternator, the house bank and start bank will need both their negtives connected to the engine.



so in a round-a-bout the answer is YES



But if under no circumstances ever will the engine charge the house bank, then "Technically" the starter battery could be completely isolated from the house with no common ground.

I want to keep the engine/alternator/ start battery isolated. If the start battery is dead, I have a long set of jumper cables that will reach the house bank.

[Zil]

There is no reason your house bank "needs" to share a common ground with the engine.

[pdervaux]

How do you will charge the house battery?

Pascal

[GordMay]

Greetings and welcome aboard the CF, Pascal.

[mrybas]

Originally Posted by pdervaux

How do you will charge the house battery?



Pascal

Primarily with solar and a wind generator. A Honda 2000 with a battery charger as backup.

[pdervaux]

If the charge circuits are totally isolated, the ground circuit can be separated too.

[OS2Dude]

Originally Posted by mrybas

The alternator only charges the start battery. There are no other charge sources connected to the start battery. Do the house battery bank and start battery need to be ground together?

Related question, same situation. If I connect Start (AGM) GND and House (LFP) GNDs together, will that affect the shunt on the house bank?

Some DC-DC chargers are for Isolated systems, others not. So, is there a reason to NOT connect the grounds?

[SailingHarmonie]

Our house (24v) and engine & generator starting battery (12v) do not have their negatives interconnected in any way. Both engine and generator are in addition isolated ground designs.

27 years and 2 circumnavigations later there has never been an issue.

[Kettlewell]

I would venture to guess that on most boats there is a common ground and the engine is included, which could lead to some confusion if you ever have someone else working on the boat.

[Bowdrie]

Engine starting batteries seldom need any real "charging" so to speak.
The watt-hours of energy needed to start a typical smallish 4 cylinder diesel is less than that which is contained in your two-cell size "D" flashlight.
One can use an isolated ground alternator to charge the house bank and a DC>DC unit to keep the engine battery topped-off.
As such there needn't be any direct high-amperage interconnect between house and start batteries and only the P/N cables from the start battery go to the engine.
And a set of jumper cables can be used if the engine battery goes south.
We can take a further step; use the engines stock internally regulated alternator to ONLY charge the start batteries and power the engines pre-heat and gages and add a second isolated ground alternator which ONLY charges the house batteries.
Now we have the best of both worlds, an independent power plant that lives in its own little world and an independent house system that has zero connections to the engine.