Mains charging bus connected batteries

[Elemental]

I have a house bank (2 x 120AH) and a seperate starter (1 x 120AH). Under shorepower, the house bank is charged by a CTEK M300 and the starter by a seperate CTEK MXS5.0 charger. Both are 8 stage chargers.

The house and engine batteries can be connected vi a breaker. Now, I never have had to do this (never flattened the engine battery) but I'm wondering what would happen if someone switches the breaker and the shorepower is connected. I don't expect sparks, but the chargers will be getting strange feedback from their respective batteries as they'll each be sensing charging output from the other. I presume chaos will reign....

Also, I could remove the starter batter, and rely on charging the engine battery via the connected bus couldn't I? The M300 is good for banks up to 500AH. That would rely on me switching/breaking the bus connection though.

 

[dt4134]

I have a house bank (2 x 120AH) and a seperate starter (1 x 120AH). Under shorepower, the house bank is charged by a CTEK M300 and the starter by a seperate CTEK MXS5.0 charger. Both are 8 stage chargers.

The house and engine batteries can be connected vi a breaker. Now, I never have had to do this (never flattened the engine battery) but I'm wondering what would happen if someone switches the breaker and the shorepower is connected. I don't expect sparks, but the chargers will be getting strange feedback from their respective batteries as they'll each be sensing charging output from the other. I presume chaos will reign....

Also, I could remove the starter batter, and rely on charging the engine battery via the connected bus couldn't I? The M300 is good for banks up to 500AH. That would rely on me switching/breaking the bus connection though.

I don't expect there would be many problems, the batteries would equalise themselves and the chargers should cope with that. You'd get a similar-ish dip in voltage if you were charging a battery on shorepower whilst using it to start the engine.

When I bought my boat the PO had installed a shorepower charger but had obviously got confused with the result that the starter battery wasn't charged under shorepower. Once I found the problem, which cost me a starter battery in the meantime, I just used jump leads from time to time to sort out the starter, until I could re-wire things properly. Never had a problem with it.

 

[Elemental]

I don't expect there would be many problems, the batteries would equalise themselves and the chargers should cope with that. You'd get a similar-ish dip in voltage if you were charging a battery on shorepower whilst using it to start the engine.

When I bought my boat the PO had installed a shorepower charger but had obviously got confused with the result that the starter battery wasn't charged under shorepower. Once I found the problem, which cost me a starter battery in the meantime, I just used jump leads from time to time to sort out the starter, until I could re-wire things properly. Never had a problem with it.

As I thought, but connecting them (in order to shore charge the engine starter) is a hassle, so my primary concern is really about accidentally having two, 8 stage chargers, connected to the bank...

 

[dt4134]

As I thought, but connecting them (in order to shore charge the engine starter) is a hassle, so my primary concern is really about accidentally having two, 8 stage chargers, connected to the bank...

The batteries are going to stay within a reasonable range of voltage & current. If you've suddenly got a voltage drop when the battery is on trickle charge, for example, then it should (if the bumpf on my multi-stage charger is correct & yours is the same) just cause it to restart the cycle.

If you are really concerned you could always just turn off your chargers, link the batteries and turn one of them back on.

Personally, I wouldn't be too worried. If your chargers are not going to go over the voltage limit for the type of battery you've set, and are not going to deliver too much current, what's the issue. Even with two in parallel they shouldn't pump current through over a sustained period to boil the batteries.

Between those limits you've only got inefficiencies to worry about, and as you say connecting them would be an occasional accidental event.

 

[Stork_III]

I have a house bank (2 x 120AH) and a seperate starter (1 x 120AH). Under shorepower, the house bank is charged by a CTEK M300 and the starter by a seperate CTEK MXS5.0 charger. Both are 8 stage chargers.

The house and engine batteries can be connected vi a breaker. Now, I never have had to do this (never flattened the engine battery) but I'm wondering what would happen if someone switches the breaker and the shorepower is connected. I don't expect sparks, but the chargers will be getting strange feedback from their respective batteries as they'll each be sensing charging output from the other. I presume chaos will reign....

Also, I could remove the starter batter, and rely on charging the engine battery via the connected bus couldn't I? The M300 is good for banks up to 500AH. That would rely on me switching/breaking the bus connection though.

On my boat the emergency starter switch connects the house battery to the output side of the starter battery switch, so the starter battery can be kept isolated. If it flat why? duff cell, so don't connect it to a good battery. Come and see if you wish 2 HR's away from you.

 

[Elemental]

On my boat the emergency starter switch connects the house battery to the output side of the starter battery switch, so the starter battery can be kept isolated. If it flat why? duff cell, so don't connect it to a good battery. Come and see if you wish 2 HR's away from you.

I don't connect it - well, never have yet. I suppose the only reason it might get flattened is if I left the engine ignition on for a long period of time...
I'll look out for you when I'm next at the boat.

 

[VicMallows]

Both are 8 stage chargers.

Just intrigued what the EIGHT stages are? ... never heard of that before?

Vic

 

[VicS]

Just intrigued what the EIGHT stages are? ... never heard of that before?

Vic

From one of the manuals:

The battery charger has an 8-step fully automatic charging cycle:

Desulphation
Desulphation with pulses recovers sulphated batteries. Indicates with lamp 1.

Soft start (Lamp 1)
Start mode for the charging cycle. The start phase continues until the battery’s terminal voltage has risen above the set limit, at which
point the charger switches to bulk charging. If the terminal voltage has not passed the voltage limit within the time limit, the charger
switches to fault mode (lamp 0) and discontinues the charging. If so, the battery is faulty or its capacity is too large.

Bulk (Lamp 2)
Main charge when 80% of charging takes place. The charger delivers maximum current until the terminal voltage has risen to the set
level. Bulk has a maximum time, at which point the charger automatically switches to Absorption.

Absorption (Lamp 3)
Complete charge up to virtually 100%. The terminal voltage is maintained at the set level. During this phase the current tapers
successively. Once the current has tapered to the set limit, this phase switches to being timed. If the total time for Absorption exceeds
the time limit the charger automatically switches to maintenance.

Analysis (Lamp 3)
Testing self-discharge. If self-discharge is too high, charging is discontinued and fault mode is indicated.

Maintenance charging - Float (Lamp 4)
Charging at constant voltage.

Maintenance charging - Pulse (Lamp 4)
Charging varies between 95% and 100% state of charge. The battery receives a pulse when the voltage drops and keeps the battery
in perfect condition when it is not in use. The charger can be connected for months at a time. The charger continuously measures the
terminal voltage to determine whether a charging pulse should be initiated. If the battery is loaded and/or the battery’s terminal voltage
drops the charger starts a charging pulse until the terminal voltage reaches the set level. The charging pulse is then discontinued and
the cycle is repeated infinitely. If the terminal voltage drops below a lower limit, the charger automatically goes back to the beginning
of the charging curve.

Recond (Lamp 5)
This mode is used to recover deeply discharged flooded batteries. Recondition of deep discharged batteries. The voltage increases
with reduced current for a limited time period. The higher voltage starts some gassing and mixing of the acid, which is beneficial for
both battery capacity and expected life. Note that the battery could emit explosive gas during Recond. Recond is performed between
Analysis and Maintenance​

 

[mitiempo]

I think a few of those 8 stages are more for advertising purposes than actual purposes - but it worked as you bought 2.

As far as paralleling the batteries with both chargers connected it isn't a problem. One will likely defer to the other. Chargers do not pump current, they have differing voltage settings depending whether they are in bulk, absorption, or float stages. The batteries accept current up to the maximum output of the charger (or alternator) depending on their internal resistance, which relates to their state of charge. As long as 2 chargers have the same voltage settings, a battery at a given state of charge will accept the same amperage from each, even if the chargers are of different amp ratings, as long as the smaller can supply what the battery will accept. The only way to increase the current to a battery is to raise the voltage.