Using circuit breakers with VSRs

[dusan19]

Hello,
I am going to add a house battery in addition to the starter battery and I am looking into using a VSR instead of a manual switch. I am going to add a current protection at each side of the VSR to protect those wires, as instructed. I was wondering if I could use circuit breakers here instead of fuses, since I could also use them as switches to cut off batteries when Im not using the boat for a longer period.

I attached a diagram of what I wanted to do.
Now, I am not sure circuit breakers are a viable option here as DC circuit breakers are current directional (the ones I have).
I would basically have to wire them such that they are directed from the first battery towards the VSR, and from the VSR towards the second battery, having in mind that the alternator is attached to the first battery, as that is where the current is going while charging (i think).
My concerns:
1)Is there a situation where the current could go in the other direction and cause the circuit breaker failure, for example if the current is drained from the second battery to the first?
2) Do i need the circuit breaker 2 at all since the circuit breaker 1 is on the same line, the only place where the current can diverge is to the VSR ground terminal which is also fused with a low amp fuse of a few amp rating.

Does anyone have experience with using circuit breakers with VSRs?
Opinions and advices are much appreciated
Cheers

[smac999]

I doubt the breakers will care which way the current is going. I don't understand the need to disconnect part. the VSR will disconnect itself when the batteries stop charging.

[cal40john]

Originally Posted by smac999

I doubt the breakers will care which way the current is going. I don't understand the need to disconnect part. the VSR will disconnect itself when the batteries stop charging.

What happens when the VSR fails as a short?

[CassidyNZ]

Why would you want to complicate your life with this device? Is a manual switch too much work? A manual switch has an infinitely less chance of failure. Don’t complicate your life by putting labour saving devices into your systems. KISS.

[noelex 77]

A lot of high current DC circuit breakers are directional (a magnetic field is used to quench the arc), but not all.

Most of the marine thermal DC breakers are not directional, and these should be OK . The one thing to watch is the IC rating of the circuit breaker. This may be too low if the battery banks are large.

[YANDINA]

We have been selling 100 amp VSRs for 28 years now and frequently get that question.
The question that we ask is "What are you trying to protect with the fuses or circuit breakers"?
Our Combiner 100 already has a built-in fuse in the event it had an internal short so you don't need to protect that.
So all you are protecting is the copper wire between the batteries which in a majority of cases is less than a couple of feet.
The ABYC standards requiring a fuse close to the positive terminal doesn't apply to all situations, in particular starter motor cables or parallel jumpers.
Unless the VSR cables are exposed to mechanical damage that could pierce the insulation against a metal bulkhead and cause a fire, spending $30 per breaker to protect $1.00 of copper wire makes little sense.
Personally I would prefer to see the money spent on conduit to protect the wires if they are exposed to damage in the first place rather than shutting the barn door after the horses got out.
Battery terminal mounted disconnect switches, however, are an excellent investment for emergency isolation and for separating parallel batteries for diagnosis.

[mitiempo]

Originally Posted by dusan19

......I was wondering if I could use circuit breakers here instead of fuses, since I could also use them as switches to cut off batteries when I'm not using the boat for a longer period.
------------------------------------------------------------------------------

Use fuses. Less expensive and there is no reason to ever cut off the batteries that I can see. The VSR will automatically separate the batteries when there is no charge current present. When there is you want it to combine to charge both battery banks.

While Yandina thinks you do not need protection for $1 of wire you do to protect the boat is is on.
-------------------------------------------------------------------------------------

Now, I am not sure circuit breakers are a viable option here as DC circuit breakers are current directional (the ones I have).
-------------------------------------------------------------------------------------
I have not seen marine rated circuit breakers that are directional - eg Blue Seas. What breakers do you have? What is their AIC rating?
-----------------------------------------------------------------------------------

The forum states this reply is too short for some reason.

[CassidyNZ]

Originally Posted by mitiempo

The forum states this reply is too short for some reason.

If you’re modifying a comment within a quote, the forum doesn’t see it as a post so you have to also post outside of the quote for it to be recognised as a post. I suspect that your line above achieved that.