Battery to battery load

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Matthewbalzan

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I have a 260ah agm house battery which connects to a 105ah bow thruster battery with a charge relay in between. I am noticing that as soon as I switch on the mains, a load of 2.5amp is measured, supposedly goong from the house to thruster battery. Over time it decreases, in about 2 hours to somewhere around 0.8amp but stays that way. Is this normal and of no concern? I was given advice to remove the charge relay and put a victron dc to dc charger instead which will allow me to shut off charging between batteries when I wish. On this note I am however concerned of doing damage to house battery since whenever I operate the thruster, the relay shut off connection so to not draw big amp loads from house. Will the dc to dc charger do the same automatically? Thanks
 
You don't say what the voltage of the bow thruster and house batteries are before you turn on the mains.

From what you say the bow thruster is topping itself up to equalise the voltage.

Personally, I have my winch battery connected to the starter motor as I use the winch with the engine on.
 
Sandy said:
You don't say what the voltage of the bow thruster and house batteries are before you turn on the mains.

From what you say the bow thruster is topping itself up to equalise the voltage.

Personally, I have my winch battery connected to the starter motor as I use the winch with the engine on.
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I have a solar panel so I find my house always 13.1-13.3. the thruster battery usually is 12.8-12.9 as I rarely use the thruster. However with mains off the solar charge doesn't transmit from house to thruster battery when i am not on boat
 
Does 'switching on the mains' mean that a mains charger becomes active? I suppose so, as the relay closes. But where are the 2.5 amps being measured? Is it on the AC side? That could be a typical AC current draw for a 25A charger...
 
I am guessing that OP is seeing 2.5 amps out of house battery in to thruster battery when he turns on a mains charger. This diminishes to .8 amp after a while. I think that would be normal as charger via house battery tries to bring thruster battery up tom 14v. I dont think there is any problem. ol'will
 
By mains I mean main switch, as that is where both batteries are connected so when I am off the boat and main switches are off there is no connection between batteries.

I want to know if this load between batteries (measured at both ends) is normal and nothing to worry about, especially since I always have at least approximately 1 amp drawing from the house to thruster battery
 
Matthewbalzan said:
By mains I mean main switch, as that is where both batteries are connected so when I am off the boat and main switches are off there is no connection between batteries.

I want to know if this load between batteries (measured at both ends) is normal and nothing to worry about, especially since I always have at least approximately 1 amp drawing from the house to thruster battery
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OK, so no mains (240V AC) charger involved.
If the relay mentioned is the bi-directional voltage sensitive type, this should open immediately every time the thruster is used, draining the thruster battery only. This could result in a voltage difference between thruster battery and house battery (depending on house battery loads and SOC at the time). The current you measure could be an effect of the two batteries equalizing when the relay is closed, possibly by solar charging.
However, if you normally find the house battery voltage at 13.1 - 13.3v, that would indicate current going in, not out. Could the shunt be wired to measure solar yield rather than in/out of battery?
 
BabaYaga said:
OK, so no mains (240V AC) charger involved.
If the relay mentioned is the bi-directional voltage sensitive type, this should open immediately every time the thruster is used, draining the thruster battery only. This could result in a voltage difference between thruster battery and house battery (depending on house battery loads and SOC at the time). The current you measure could be an effect of the two batteries equalizing when the relay is closed, possibly by solar charging.
However, if you normally find the house battery voltage at 13.1 - 13.3v, that would indicate current going in, not out. Could the shunt be wired to measure solar yield rather than in/out of battery?
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Yes the relay opens when I operate thruster to drain its battery only. I find the house 13.3 because when I am not on boat the house keeps charging by solar then goes to float with mppt controller, but since the main switch is off thruster battery will not charge with solar when i am not on boat. Therefore I can understand that as soon as i turn on main switch the thruster battery starts getting solar charge through house. At the moment this load is 3.5amp and am seeing it going lower...that would be normal?
 
The current might be normal, but in your situation I would consider rearranging the wiring so that the main switch only effects the house loads, leaving the thruster battery connected, so that this also can be charged by solar when the boat is unattended.
 
BabaYaga said:
The current might be normal, but in your situation I would consider rearranging the wiring so that the main switch only effects the house loads, leaving the thruster battery connected, so that this also can be charged by solar when the boat is unattended.
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Nothing wrong with switching all of the loads off when leaving the boat, but switching the charging off isn't the best idea.

The VSR (assuming it is a VSR) should be wired between the batteries, not after the isolator switches..
 
PaulRainbow said:
Nothing wrong with switching all of the loads off when leaving the boat, but switching the charging off isn't the best idea.

The VSR (assuming it is a VSR) should be wired between the batteries, not after the isolator switches..
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I think will do a rewiring in winter....remove the connection from the main switches and install a dc charger instead of charge relay. That way I will have charging available also when I am not on boat
 
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