Second battery mod with Add-a-Battery (SX210)

[Gonzalo]

Hello community!

Happy Monday!
Yet another thread about adding a second battery. After reading many existing threads, I decided to go with Blue Seas Add-a-Battery. I have just a couple of questions and I will try to keep this simple.

Please look at the schematic and picture attached.



1) The "A" fuses protect the relay from overcurrent, and the gauge of the cable and rate of both fuses "A" should depend on the charging current that the stators provide to the batteries. (Of course I can always put a much higher amp fuse, but it's always good to dimension the system well. So the first question is , does anybody know the approximate charging current provided by the stators on an SX210?

2) The B and C fuses are already on the boat (actually the B fuses are 2 different ones, one for the radio and one for the rest) , so there is no problem here. But the C circuit is for the automatic bilge pump, which is always connected to the battery, even when the battery switch is off.
My question is... should I connect the auto bilge pump to the House battery (like I did on my diagram) or to the Start battery?
I'm wondering how it is connected on the Yamaha boats that come from the factory with 2 batteries. Does anybody know to which battery the auto-bilge pump is connected to?

Thank you very much
Gonzalo

 

[JasonB]

2 - My boat only came with one battery, so I don't know how Yamaha wires the bilge to the boats with two. But, if I was doing what you are (and I have done so with my old inboard ski boat), I would wire the bilge pump to the house battery. I only want that start battery to start the boat. I guess you could always lift the battery cables from each battery and test the float to see if which one powers it.

1 - After much digging in these forums, I remember someone did some real world testing on their charging stators. If I remember correctly, they found that at most (during high rpms on the engines) the stator outputs approx. 28 amps of charging current. Less at lower rpms.

When I go to install my second battery, I'll use the Blue Seas Add-a-battery setup again.

 

[marcham]

60A will be plenty for the acr fuses.

 

[Gonzalo]

2 - My boat only came with one battery, so I don't know how Yamaha wires the bilge to the boats with two. But, if I was doing what you are (and I have done so with my old inboard ski boat), I would wire the bilge pump to the house battery. I only want that start battery to start the boat. I guess you could always lift the battery cables from each battery and test the float to see if which one powers it.

Thank you. That's what I thought too. This is why I connected the pump to the House battery in my diagram. But I'm curious to know how it comes wired from the factory in boats that ship with 2 batteries.

1 - After much digging in these forums, I remember someone did some real world testing on their charging stators. If I remember correctly, they found that at most (during high rpms on the engines) the stator outputs approx. 28 amps of charging current. Less at lower rpms.

Awesome thank you.

 

[Gonzalo]

60A will be plenty for the acr fuses.

Thanks! I'm even wondering now if I should put those fuses or not. They are really there only to protect the ACR. If the ACR fails it can either fail open or fail close... no big deal in any way. But of course then I would need to replace the ACR instead of a fuse ...

 

[212s]

Thanks! I'm even wondering now if I should put those fuses or not. They are really there only to protect the ACR. If the ACR fails it can either fail open or fail close... no big deal in any way. But of course then I would need to replace the ACR instead of a fuse ...

Fuses and breakers are not there to protect devices like ACR's or stereos. They protect the wiring in the boat/car/house from device shorts that could draw too much current through the wire causing it to overheat and catch fire.

 

[Gonzalo]

Fuses and breakers are not there to protect devices like ACR's or stereos. They protect the wiring in the boat/car/house from device shorts that could draw too much current through the wire causing it to overheat and catch fire.

Of course, in general, yes.
But the "A" fuses on the circuit above are there for the sole purpose of protecting the ACR.

 

[212s]

Of course, in general, yes.
But the "A" fuses on the circuit above are there for the sole purpose of protecting the ACR.

Why would the ACR need to be protected, and from what? Its purpose is to carry current between batteries to allow parallel charging. The only way you would damage that relay is if you had a massive charging system with over 120a capacity. In that case you'd use a larger ACR with a higher rating.

Fuses and breakers have one sole purpose - to protect the wiring connected to it from overheating and causing a fire. Fuses are never there to protect a device. It's the device that can cause a problem if it shorts out, which draws too much current through the wiring. The fuse pops to prevent that high current flow.

 

[HangOutdoors]

I concur with @212s. You should have the circuit breakers on the battery positive cables BEFORE they reach anything. The breakers between the switch and ACR and worthless, imho. On mine I have 100 amp breakers between each battery and the switch. That way the can pop before the current draw reaches anything else.