Mystery electrical system problem - not sure how to proceed.

Bill K · Posted: Thu Oct 24, 2013 9:45 pm Post subject:

Sunbeam,

I think where some of the confusion comes from is that the wiring diagram's don't show all of the fuses that you say you have.

Bill Kelleher

Ray · Posted: Thu Oct 24, 2013 9:54 pm Post subject:

Hi Bob,

I'm not one to stick my nose in where it's not wanted, but I thought I'd offer a few thoughts...

Sunbeam · Posted: Thu Oct 24, 2013 10:04 pm Post subject:

C-Nile · Posted: Thu Oct 24, 2013 10:08 pm Post subject:

Something happened to me year's ago. One day, my car would not start. The battery was fine, and there was no visible signs of corrosion. The (hot side) battery cable looked fine on the outside, but when I checked, the wire was corroded a few inches inside the cable. The starter could not get sufficient current to crank the engine over.

Is it possible that you have a problem with one of your cables? Internal decay or a defect could cause it to heat up under load and possibly blow a fuse.

Rich

Ray · Posted: Thu Oct 24, 2013 10:14 pm Post subject:

Sunbeam,

Re-looking at your diagram, it seems to me that if EITHER of your batteries, start or house, were very low, then the instant that either the ACR or the COMBINE switch joined them together, then a HUGE amount of current would be sent through the safety switch fuse as the good battery tried to transfer energy into the depleted battery (the physics tries to make this happen instantaneously).

In the case of the ACR, it is designed per the installation instructions such that the wire, likely 16ga, offers quite a bit of resistance to this in order to limit the current, and the 30A fuses in those wires (I assume you have them) would protect the wires themselves. When ACR-combined, though, there are then THREE fuses in series connecting the two batteries together.

[EDIT]
2 issues -
1) Looking back at your pictures, I don't see any fuses in your ACR wires that join the batteries. These are recommended by Blue Sea in the installation instructions (http://assets.bluesea.com/files/resources/instructions/990170140.pdf). This means that in all of the dissimilar batteries cases, the 30A safety fuse would be the only thing trying to limit surge currents. This fuse would definitely open if the batteries were far apart is charge when the ACR closed.
2) I was working from memory on other installations for the ACR - the wire sizes (16ga, etc.) are a function of the charging currents available in your system. The wire (and fuse) sizes are recommended in the installation link above.

The fuses in the ACR lines are the same value as the safety switch fuse in your case, so in the case of an immediate spike/surge that did run through the ACR wires, the weaker of any of those three would blow first. Could it be that the the safety switch fuse was just a bit shy of the two ACR fuses when the ACR combined? Maybe test a 40A fuse in the safety switch and see if one of the ACR 30's then blows first?

Alternatively, in the case of the master switch COMBINE (again with dissimilar battery levels), then the 30 safety switch fuse is the only one in the way of this large current surge, which could blow immediately.

This, again, is ONLY for the case that one or the other battery is very low compared to it's companion.

It also might make sense to take static voltage measurements on the two batteries at a time of similar occurrences (engine just having run, etc.). Or, also, after both have been resting for some time to see if there is a weak cell, etc. in one or the other of them.

Just some more thoughts.....

Sunbeam · Posted: Thu Oct 24, 2013 10:23 pm Post subject:

anchorout · Posted: Thu Oct 24, 2013 11:04 pm Post subject: Battery monitor shunt

Sunbeam:
The only thing I question is the way the battery monitor shunt is wired. You are creating a potential (much as a highly corroded terminal might do) between the two battery grounds. This could create all sorts of problems when you switch or eliminate one of the batteries. Might I suggest you tie both battery negatives to one side of the shunt, and the ground plane to the other.

anchorout · Posted: Thu Oct 24, 2013 11:37 pm Post subject: crazy computer

The computer cut my edit off.

Sunbeam:

I am headed to the Gulf Brat Gathering, but when I get back to my boat, I,ll see how the shunt is wired on it and get back to you. The way the schematic is wired, the shunt is only monitoring the charge through the house battery. That battery is always on line so that would work, but the accuracy would be in question as the current is also splitting to the starter battery.

Sunbeam · Posted: Thu Oct 24, 2013 11:40 pm Post subject: Re: Battery monitor shunt

Ray,

Looking at the ACR instructions, I see what you mean about the fuses in the ACR cables. I had this installed by a tech (a while back now), and at the time I didn't really understand enough to question how it was done, which was without fuses (although interestingly, the Blue Sea tech person didn't catch it either). So it looks like I need a 75-90 amp fuse in each of those #6 cables leading from "A" and "B" on the ACR to the two "cold" sides of the battery switch. Duly noted (my lazarette is going to be like a fuse depot!). I guess I may finally get a crimper for #6 battery lugs.

anchorout · Posted: Fri Oct 25, 2013 12:05 am Post subject: blasted computer

Glitch

Sunbeam · Posted: Fri Oct 25, 2013 12:25 am Post subject: Re: Are you in sales?

anchorout · Posted: Fri Oct 25, 2013 12:27 am Post subject:

One good thing, now you know that you should be able to run the boat on ""combine" and not blow the house fuse, as the ACR would be out of the circuit.

Ray · Posted: Fri Oct 25, 2013 6:14 am Post subject: Re: Battery monitor shunt

AstoriaDave · Posted: Fri Oct 25, 2013 10:32 am Post subject:

Sunbeam,

That looks good, with the same caveats Ray identified. Your plan to move the safety hub with its 30 A fuse to the other side of the main switch, will remove both.

My only reservation is that later you may decide you need more capacity for some rare, "emergency" set of conditions, as I mentioned earlier. However, with the safety hub past the main switch, using the two safety hub terminals which bypass the 30 A fuse, add ons (separately fused) could solve that issue. The existing 10 ga wire will be unused after you go to 6 ga for the main feed to the helm, so there is some capacity there ... don't recall what you calculated for maximum load on that wire. In lieu, with 6 ga wire coming off the safety hub, is there any reason you can not increase the rating of that fuse from 30 A to a higher one, feeding add ons from the positive buss?

The problem of a surge of current from a fully charged battery flowing to a nearly dead battery through that 30 A fuse will be moot when the safety hub is moved.

thataway · Posted: Fri Oct 25, 2013 11:06 am Post subject:

Sunbeam, when leaving the boat for any length of time, disconnect the + battery cables. If the boat is in the water, then the bilge pump auto circuit would have to be left connected. I have never had any issue with ACR depleting the batteries over days.

Ray, you don't run with the switch on combine, that is why there is the ACR. Pretty much established that a surge when the batteries are combined thru the ACR, that could blow the 30 amp fuse. Looks as if this has been changed.
Only Sunbeam knows exactly how this is wired.

Ref. the tt relay, if you put it on the diagram should be shown properly.

I suspect we will see the corrected, or proper diagram to avoid these issues.

Sorry I can not draw diagrams from the I pad...

Back to the Gulf Coa st gathering.