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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.
That sound about right, the Combiner100 can handle peak inrush currents of 250 amps so you are well within limits. If you do decide to fuse a combiner circuit they should be "slow blow" fuses. However there is a problem with slow blow fuses. They make them slow blow by increasing the amount of metal to absorb the momentary heat but that thermal cycling can eventually cause hairline cracks and the fuse goes open without actually having been overloaded.
But what is the fuse protecting?
Any path to ground inside the Combiner is already fused. So all the fuse is only protecting is the cable between the batteries in case it got a mechanical short to ground. If that is what you are protecting you need TWO fuses, one at each battery post since either battery would supply current to the short in the cable.
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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 should not be turning on until one or both sides are at about 13 volts for at least 30 seconds. Depending on voltages and charge conditions it may not stay on for more than a few seconds since it always protects against one battery stealing charge from the other.
The green remote control wire on the Combiner doesn't carry any current, it just senses remote control voltage. If you have this connected to anything then even a little leakage from +12 can cause it to try and turn on.
The green remote control wire on the Combiner doesn't carry any current, it just senses remote control voltage. If you have this connected to anything then even a little leakage from +12 can cause it to try and turn on.
I trimmed them back to a few inches and put a piece of heatshrink over the ends, so they are floating. I do have plans to use them in a monitor project but haven't built that yet.
I'll look more closely at this today, but the combiner between the starting batteries closes much more quickly than 30 seconds after applying charge voltage, perhaps only five seconds - if it isn't already closed as noted above. The combiner to the house battery, though, does follow about 30 seconds later. Perhaps it is surface charge that hasn't bled off that's keeping the combiners active? I'll allow them to settle, off charge, for a few hours and see if the combiner is still cycling.
Ok, my useless take on the to fuse or not to fuse between bat.'s and combiner. Elusive, I understand what you are saying, and like the extra protection (as me likey safty on my boat!!), BUT, I have NEVER seen ANY boat with either a combiner or a battery isolator with fuses between them. Never. Hmmmmmmm??? So the question is, do they not do it to save money (extra fuse + extra wiring...), OR, do they not do it for the reasons stated by "Yanda", it's not pratical because more connections, more wires, more terminals, more breaker/fuses to fail....?
In my case, I have the BEP battery cluster (717-100a) for 2 motors, and 3 battery banks (it has 2 combiners). My starting batteries are about 5' away from the switches/cluster. But, my house battery is a long way away, about 10' or 15' from the switches.
I'm moving away from the thread topic here, perhaps, but the combiners do cycle two hours after turning the charger off. Both do, between the starting batteries and to the house battery, which is at 12.6V under significant loading, about 7A, with the combiner open.
With no load and charger off, the starting batteries showed 12.79V last night, and 12.86V this afternoon - when it is quite warm here, about 93F. I turned a few cabin lamps on and the voltage dropped about 0.1V and, after a few minutes, the combiners appear to have stopped cycling. That suggests to me that the threshold voltage is well-controlled and critically close to the float-mode voltage from the charger. I suppose I should check the accuracy of my multimeter.
I removed the cell covers and see no significant loss of electrolyte, and only the occasional bubble with the charger on, so I don't think the batteries are being overcharged. The specific gravities, though, are apparently about 1.30, a little high; 1.265 is normal full charge, I understand, with healthy conventional chemistry. Is 12.86V (~1.30SG) excessive or within reason at this temperature?
A slowly-cycling combiner probably isn't particularly problematic but it is unexpected. Is the non-charging cycling indicative of something else I should consider?
The 30 seconds we quote for it to turn on once the voltage reaches about 13.1 is a maximum. The timing components are not precision. The voltage threshold is controlled fairly tightly at about 13 volts. It is not adjustable, it relies on precision components that do have a small tolerance.
Combiners should stay on at the float voltage of chargers which is typically about 13.6 but some are lower. If the charger is on and its float voltage is in the vicinity of the Combiner threshold, then cycling would be normal.
If the battery has just come off charge and there are no other loads, it will have an artificially high phantom voltage that can cause the Combiner to cycle. Fully charged voltage is about 12.8 that gives a good tolerance under the threshold. This phantom voltage cannot support any load so when the Combiner turns on, the phantom voltage drops to zero and the Combine turns off. Since it draws no current when off the phantom voltage can rise again and cause it to cycle.
Ok, my useless take on the to fuse or not to fuse between bat.'s and combiner. Elusive, I understand what you are saying, and like the extra protection (as me likey safty on my boat!!), BUT, I have NEVER seen ANY boat with either a combiner or a battery isolator with fuses between them. Never. Hmmmmmmm??? So the question is, do they not do it to save money (extra fuse + extra wiring...), OR, do they not do it for the reasons stated by "Yanda", it's not pratical because more connections, more wires, more terminals, more breaker/fuses to fail....?
In my case, I have the BEP battery cluster (717-100a) for 2 motors, and 3 battery banks (it has 2 combiners). My starting batteries are about 5' away from the switches/cluster. But, my house battery is a long way away, about 10' or 15' from the switches.
So, what is the answer? And, should I be installing a breaker to protect my 15' house bat. cable?
When customers ask if the fuse is necessary my "official" answer is that the fuse protects us, not your boat. If you don't have fuses at both battery posts and your boat catches fire we can say it was installed incorrectly.
If you check with ABYC, they have the same problem. If they were to say you don't need fuses and someone had an accident they could be open to a lawsuit.
So my answer is YES fuses must be in stalled at both battery positive terminals.
Practical sailors understand these paranoia situations and make up their own mind based on risk-verses-cost and common sense.
If it is a metal boat or vehicle where a cable would have a grounded environment then serious consideration should be given to the increased risk, even though minimal.
If it is a glass boat I suggest you run the positive and negative cables by separate routes so if there is a catastrophic mechanical incident, the chance them shorting is minimal.
Despite my official position, I lived aboard a 71 ft steel boat for 14 years with massive battery banks and did not use fuses on the Combiner circuits or the parallel switch Off/1/Both/2 circuits. In emergency situations where it is imperative you have power for radar, depth sounder, radio, engine starting, lights etc., it is no time to be crawling round the engine room with a flashlight trying to find a blown fuse that is "protecting" you.
Thanks GTBecker for the detailed follow up on what was going on with your setup and to Yandina with the insight to the specific functioning of the C100. I learnt sumthin today!
FWIW, my battery management project has started to mature.
My boat is used, mostly, for instrument development. It spends a good deal of time in the lift behind my home, on shore power, while software on its helm PC is developed and tested remotely via WiFi. Most onboard instruments and radios are running and I've chosen to continuously power them by battery, not by power supply or converter. Naturally, the battery needs to charged but I don't want the project to "see" the charger, so I've built a monitoring and switching device to manage two alternating batteries.
I have two Group 27 dual-purpose (semi-deep-cycle) house batteries that take turns powering the project, radios and instruments, one charging while the other powers the load, switched by a pair of relays in a sealed enclosure near the batteries. The switching is controlled by a processor/display/keypad at the helm. The batteries are briefly paralleled to the load after the discharging battery reaches a threshold (currently 11.80v, 50% discharge, software-adjustable) then that battery is switched to charge while the just-charged battery powers the load, so the result is a perpetual battery that averages about 12.4v. The switching/charging cycle is about four hours under the current load and charger.
To be sure, this is a special configuration that suits my needs but perhaps it will interest some of you. A camera that watches the battery controller (for as long as it is in testing) at the helm is online: http://www.ustream.tv/channel/hydralight .
