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... must be large enough to handle the alternator output if it gets all its current - or more if a discharged house battery is suddenly combined with charged start batteries.
I had a 50A fuse at the house battery post. I had turned the shore-power charger off at the AC panel to test it's RF noise and forgot to turn it back on, so the house battery depleted overnight. I turned the charger on in the morning. The fuse blew shortly after that, I assume when the combiners switched.
That raises a dilemma. Should the combiner connect to the house battery post, unfused?
If the fuse blew it means that the circuit was drawing too much current. If no fuse was present, the wire could have burned up potentially causing a fire
Fuses & circuit breakers are designed to protect the wire connected to them and are important safety devices
IMO a circuit breaker would be a better choice for this application as it can be reset
If this problem persists, you will need to find out why the circuit is overloaded and take appropriate action
... it means that the circuit was drawing too much current...
Yes, of course. I believe the reason that happened is because the depleted house battery was connected to two charged start batteries when the combiner relays closed after seeing the charger voltage; the current between the batteries was greater than 50A, I suspect. I think I understand why this happened. The question is what to do to safely prevent it from happening again.
It seems to me that I either use a 100A fuse (matching the combiner's maximum) with both combiner and house on the fused side - or no fuse on the combiner, like the starting batteries. The dilemma: a 100A fuse is too large to protect the house wiring. I can use two battery-post fuses, I suppose, 100A for the combiner and 50A for the house.
I can also limit the combiner current to 50Amps and use the single 50A fuse for both combiner and house. The question then is how to limit the combiner current. Yandina provides a clue. Yandina C100 combiners use a minimum length of #10 wire to assure that the current through them is limited to 100A by deliberately using the wire resistance as a power resistor that dissipates the resulting power loss over its length, I believe. Yandina's warranty is voided if the provided red #10 wires are shortened; lengthening them is fine since that just reduces the peak current.
In another thread here ("A DIY simple way to prevent voltage drop at the helm"), using a length of deliberately slightly-small wire between the start battery and a small holding battery near the instruments is proposed. The wire resistance is used to sufficiently isolate the instruments from starting droop. Someone complained that this is unsound engineering. If fused, I think it is effective, safe and clever - perhaps the example of creative sound engineering. While cranking, the amount of power dissipated as heat over the entire length of wire from helm to engine is probably undetectable; it can, I'll bet, be guaranteed to pose no risk of fire.
It seems to me that I can do the same to limit my combiner current to 50A by using, (12.6v-10.5v)/50= 0.042ohm of wire between the batteries through the combiner. That's the unloaded voltage difference between fully-charged and depleted, the drop that would be present across the length of wire during the initial worst-case current. It looks like 25 feet of #12 would provide that resistance, perhaps an impractical length. A proper power resistor would be more sane but would likely cost more than another post fuse.
So, I believe that two post fuses (or circuit breakers), 100A for the combiner and 50A for house, might be the wisest solution.
You seem to be looking for a "band-aid" instead of solving the underlying problem
Yes, one-time, but the house battery was just added a few months ago; it has been accidentally depleted just one time. There are two combiners, one between the starting batteries and one from one of them to the house battery. A two-bank, 12A-total charger on the starting batteries; the combiner between them is redundant, but provides 12A to the house when needed. Yandina C100, as I said, which is provided with about six feet of #10; I've lengthened them by a few feet each to get to the A/B switch and a single-pole master switch for the house battery. #8 wire is on the house battery, through its 50A fuse.
To the contrary, I am looking for a proper solution. The issue is the initial charge current to the depleted battery from the starting batteries when combined due to the appearance of charge voltage from either the shore power charger or the alternator. This won't happen again, I hope, but could since all it takes is a depleted house battery to repeat the event. Why do you believe that two fuses is a band-aid?
I may not understand your situation, but it sounds like the weak link in your wiring is between starting batteries, and a small battery near the helm used for electronic equipment. In your message you said the house wiring cannot take 100 amps as if that is the fundamental basis for your problem.
Two possible solutions if that is the case: replace, or parallel the house wiring with suitable wire; or move the small battery close to the starting battery with suitable wire connecting the batteries through the combiner.
Another possibility is a smaller capacity combiner. I have the yandina 50 and I am pleased with its performance It appears to have been discontinued, but maybe there is a way to trade or find one somewhere.
The band-aid comment was directed at the suggestion of adding wire to create a voltage drop instead of determining why a 12A charger was blowing a 50A fuse.
First, I don't see the advantage of the ACR between the starting batts. The existing switch provides (I assume) a connection should an emergency start become necessary.
An ACR between each starting batt and the house batt will allow each engine to charge the house batt and allow full charger output to the house batt once the starting batts are charged
My guess is that the depleted house batt acted like a short circuit and blew the fuse.
I would get the house batt tested and replace the fuse with a manual reset circuit breaker
... parallel the house wiring with suitable wire...
Quote:
Originally Posted by Elusive
... determining why a 12A charger was blowing a 50A fuse. [] ... the depleted house batt acted like a short circuit and blew the fuse.
The charger is not blowing the fuse, nor is the house wiring insufficient. Yes, the depleted house battery blew the fuse when the starting batteries yielded more than 50A when they were combined with the house battery. The combiner between the starting batteries serves to charge both when under way regardless of the A/B switch position.
I apologize for using too many words to describe the problem; I've confused you more than I've helped solve the issue. Thanks for your responses.
Edit: When in doubt, RTFM. The Yandina C100 installation guide says, on Fuses & Circuit Breakers:
"Accepted wiring practice guidelines dictate that all 12
volt circuits except starter motor leads should be fused,
however there is no path to ground inside a battery combiner
that can carry any significant current should it suffer an
internal failure. Fuses in the battery leads to the combiner
only provide protection from a short to ground on the battery
cables themselves which must pierce the insulation. Conduit
covering can reduce this risk.
If it is a metal vehicle and the unprotected cables are
close to grounded metal the risk of a short is much higher
and fuses may be a good protection. The size of the fuses
has to be much higher than the charging current available
because when the combiner first closes quite large currents
can flow from one battery to another. These battery to
battery currents are limited by the wire gauge and length of
the red wires which must not be shortened. A slow blow
fuse of approximately 30% to 50% of the total Cold Cranking
Amp capacity of the batteries in the smaller bank is a guide
to value."
That suggests, I think, a >200A fuse. I think I'll go directly to the house post afterall.
The charger is not blowing the fuse, nor is the house wiring insufficient. Yes, the depleted house battery blew the fuse when the starting batteries yielded more than 50A when they were combined with the house battery. The combiner between the starting batteries serves to charge both when under way regardless of the A/B switch position.
I apologize for using too many words to describe the problem; I've confused you more than I've helped solve the issue. I'll email Yandina.
We don't recommend fuses in the Combiner battery to battery cable unless there is a physical situation that could cause a short, for example, exposed locations on a metal vehicle or open bus bars that could have a tool dropped on them.
Fuses are not required on starter motor circuits. The reason is that there are times when the starter motor will require the full CCA capacity of the battery. So to prevent a nuisance fuse failure, the fuse would have to be rated at greater than the CCA. If the fuse is greater than the battery capacity the battery doesn't have enough amps available to blow it so the fuse is useless. In fact the wiring, mounting and exposed terminals of a fuse can increase the chance of a failure. Kiss applies here.
The same applies to the current through a Combiner when a dead battery is connected to one on charge at 13+ volts. The Combiner100 can stand 250 amps inrush current and the 10 gauge wires limit to less than this. If the combiner were forced to stay on in this situation, an internal thermal shutdown would disconnect at about 180F and stay off until it cools to about 170. This will protect the wiring from overload.
Adding a small amount of resistance does not reduce the charging voltage. As the battery on charge approaches full charge the current going into it drops to zero. As the current gets lower, the voltage drop on the wiring also goes to zero so it still gets a full charge.
GTBecker - you have misunderstood the problem and I highly recommend that you get someone qualified to determine why the fuse blew. The reason is NOT when " the starting batteries yielded more than 50A when they were combined with the house battery"
I also disagree with Yandina's statement "We don't recommend fuses in the Combiner battery to battery cable unless there is a physical situation that could cause a short, for example, exposed locations on a metal vehicle or open bus bars that could have a tool dropped on them."
Your specific situation is exactly why an overcurrent devices is necessary. A 50A fuse blew and it was not due to short circuit due to a tool, etc.
Had the fuse not been there, the circuit conductor would have been at risk.
This advice also contradicts ABYC E-11 which says that circuit protection should be installed within 7" of each battery or source of power
... you have misunderstood the problem and I highly recommend that you get someone qualified to determine why the fuse blew...
Your recommendation, and your presumptuous but incorrect declaration that the fuse did not blow as I explained (and Yandina supports) is noted, but I believe I better understand the situation than do you, Elusive.
I started the thread looking for a discussion of the pros and cons of fusing the combiner. I said: "... house battery depleted overnight. I turned the charger on in the morning. The fuse blew shortly after that, I assume when the combiners switched. That raises a dilemma. Should the combiner connect to the house battery post, unfused?", implying a reference to ABYC, quoted here frequently. I am an electrical engineer, understand Ohm's Law, and I build well-engineered systems; I believe I am qualified.
On consideration, I'll follow the combiner manufacturer's advice - taking into account your and ABYC's suggestions. Thanks for your help.
One of the reasons that I use and recommend Blue Sea Systems products is that they recommend following an accepted industry standard. Their ACR also has an overcurrent device built in, but they still recommend using an overcurrent device close to the batt.
Let's say hypothetically that your house batt is bad and causes excessive current in the charging circuit. If there is no overcurrent device, what happens ? The Yandina device repeatedly heats & cools, connecting and disconnecting the circuit ? How long does this go on ? What will finally fail ? What is the resulting damage of the failure ?
I just don't see the value in omitting the OC device whose only purpose is safety.
I hope you solve the problem and post the cause and solution so that all of us learn from your experience
OK, the stage is set. I've turned the shore power charger off and all the electronics are running. I expect I'll find a discharged house battery in the morning.
I've rigged a laboratory-grade shunt that produces 50mV for 100A. I'll place it in the house battery line tomorrow before I turn the 12A charger on, and capture the combiner closure a short time later with a handheld digitizing oscilloscope. That should show what the current into the battery is over the following eight minutes. I suspect the current will well exceed 50A, sufficient to blow the fuse, which will not be in-circuit.
I am not arguing that adherence to ABYC guidelines is ill-advised, only that the cause of the blown fuse is understood and can be replicated. I believe that you, not I, misunderstand. We'll see.
Do you know what the voltage of the "discharged" battery is? My suspician is that you are not doing the battery any favors by allowing this deep a discharge.
I do fuse my combiners, both at the combiner and at the battery--the run from one of my combiners is over 12 feet, and I would be very uncomfortable having that length of #10 wire unprotected. Granted that it can be unusual that there is a direct short in a properly wired boat--but that has been the cause of boat fires in the past, and I don't want to take a chance.
There is a chance that your current draw from a fully charged battery, to a fully depleated battery could be more than 100 amps.
Do you know what the voltage of the "discharged" battery is?
Yes, it was 10.5v when I discovered the blown fuse. The battery is a new deep-cycle, so I hope a discharge or two won't hurt it much. After the last of the electronics gives up, it won't be under additional load, I think, and will stop there. If I had a lamp or something on it, though, it might go deeper than it should.
It is my understanding based upon ABYC regs, that since there is no path to ground between the legs of the combiner, that no fuse is necessary or for that matter reccommended. In all the installations I have seen or done, each leg of the combiner goes to the battery terminal on the switch, just like the charger (which is fused, because it does ground).
Unfortunately many of the ABYC regulations are influenced by fear of litigation rather than practical boating. It is a set of standards which if followed minimize the chance of catastrophic failure and will stand up in court as diligent prudence. But as in most of life, we have to compromise on risk verses cost. We don't all drive the safest vehicle. We don't all have medical insurance. We don't fuse starter motor circuits and there is much more potential there for a battery short circuit.
If you have a budget that has room for safety items then by all means spend it and spend it wisely. Look at the sources of disaster and pick the best return for your dollar. Do you have a Carbon Monoxide detector? Would that be a better investment than a 250 amp fuse on a very reliable circuit? As pointed out, the only current carrying conductors on the Combiner are the two battery post ones. All the others are internally fused in the event of internal short. With over 40,000 sold, all on unconditional warranty, we have never had a return with a fuse blown.
Yes if the Combiner is overloaded, it will cycle on and off. That is what it does all the time. We have Combiners in the field that are 16 years old and not a single one returned under warranty for relay contact failure. On one that was returned because it was "noisy", the internal timing capacitor had mechanical damage so instead of cycling about once a minute, it was cycling about 10 times per second. It was on a fishing boat where for over a year the noise was not normally a problem but annoying at night on shore power. So running 24/7 at 600 times faster than normal the contacts were pitted but functioning fine and could have run for another year like that. Based on that field test, the Combiner can turn on and off longer than your batteries or power supply can support it.
The method I'd planned didn't work well, however, so I needed to do several cycles of discharge/start-charge to see what was happening. The Fluke digital scope, at 60Sec/division (which would have given the eight minutes I hoped I'd capture), doesn't sample the inputs sufficiently rapidly to trigger on the initial charge current rise, so it missed it and never started the trace. I found that that initial peak is brief, so I had to use 1Sec/division to trigger reliably, and 100mS/division to see real detail.
What I found was a 130A peak; it was above 100A for about 50mS, quickly falling to ~35A and slowly falling from there. I believe that is enough current, and an adequate duration, to blow the 50A fuse - although I chose to not sacrifice one, at $16.00, for this test. It is, nevertheless, lower current and shorter duration than I expected.
I noticed something interesting about the combiners. Despite having the charger turned off, with both starting batteries measuring 12.79V, the combiner between them was periodically cycling. The combiner to the house battery did not cycle while I watched it but the house battery voltage was 11.3v when I went out this morning, higher than expected, still lightly loaded with a RAM mic that had an active display although all other instruments and the helm PC were dark after running for almost 12 hours. In fact, when I later discharged it again, the house battery fell to 6v loaded and climbed to about 9.5v after being unloaded for 10 minutes or so; as I found the battery a few days ago with the open fuse, it showed 10.5v. The 11.3v of this morning is puzzling. Yandina: is it possible that the house combiner had closed for some period, too?
The outcome of this test assures me that a 50A battery-post fuse is indeed insufficient for the combiner, not a surprise, and that the inrush current very likely did blow it. The charger cannot produce such current and plays no part except to trigger the combiner closure.
My take on your test is that the fuse was either the wrong type (one time) or defective. It should be a time delay fuse that is designed for the high initial load. I still think that a circuit breaker (inverse time) is a better choice than blowing $16 fuses that aren't readily available and always seem to blow at the most inopportune moments (70 miles offshore and/or Sunday nite)
If all of the batteries and combiners are in close proximity, I see Yandina's point, even though I still like having an OC device in the circuit.
If the house battery is located remotely, I think OC protection is essential
House battery-post fuse or breaker... 
