Alternator and engine HP

[LittleSister]

When my little 1GM10 (9hp) engine is running and I move my electrical switch to both there is a distinct change in engine note and I guess this is the alternator working harder and therefor putting more strain on the engine.

To add to the advice already given by others.

The change in engine note you describe seems to me entirely normal.

When you put an additional load on the alternator, this puts an additional load on the engine. (I would not describe either as 'strain', as such a load is what they are both designed and built to deal with.) This additional load on the engine will inevitably cause some change in the engine note, and this will likely be readily audible on a small engine and somewhat discharged domestic battery, where the alternator load is a significant proportion of the total power available.

When you set the 'throttle' (a misnomer) on a marine diesel, you are not setting an amount of fuel, you are setting a speed. Put an additional load on a marine diesel and it will slow up very slightly (whether or not you hear it) then automatically increase the fuel supply to get the engine back to the original speed. As the engine is now working harder, and burning more fuel, it will quite likely sound noticeably different. That is OK!

Only if turning the second battery on causes the engine to stall, or it cannot recover to the original revs, is there a problem. Even then it's more likely to be the engine needing attention rather than the alternator, switching or wiring.

Personally, I prefer a voltage sensitive relay (VSR) controlled connection to the domestic battery (just for convenience and to make sure I never accidentally flatten the engine battery), but fitting one would not stop you being able to hear when the engine is working harder.

 

[Gixer]

Help, I’ve confused myself again!

I got a vsr and a victon BMV For Christmas!
I’m going to use the BMV to monitor my domestic battery and the vsr to link the charging between domestic and engine battery.

Question is, if I connect my battery charger to the domestic battery which will then charge the engine battery though the vsr, will this screw up the BMV readings?
My brain says it will, as the charge it records will be for two batteries but it will only monitor discharge for one.

Does this make sense?

 

[pvb]

Help, I’ve confused myself again!

I got a vsr and a victon BMV For Christmas!
I’m going to use the BMV to monitor my domestic battery and the vsr to link the charging between domestic and engine battery.

Question is, if I connect my battery charger to the domestic battery which will then charge the engine battery though the vsr, will this screw up the BMV readings?
My brain says it will, as the charge it records will be for two batteries but it will only monitor discharge for one.

Does this make sense?

If you install the shunt correctly, following the instructions, it will only record the current in and out of the domestic battery.

 

[PaulRainbow]

PVB is correct, because the VSR only parallels the battery positives, the negatives are still two slightly separate circuits, the domestic negative goes through the shunt, the engine battery does not.

 

[Gixer]

Thank you pvb and Paul.

I was overthinking it again. I couldn’t see how the Shunt on the domestic negative wouldn’t read the amps going though the positive into the engine battery.