Well I do have a question about one case that I have with ACR. It is about transients.
ACR is the Blue Sea
trade name for their combiners or VSR's voltage sensing relays.
I am using an ACR from Victron energy type Cyrix-i (100A countinous current max) on my boat (Cyrix measures voltages on both battery groups - house and start). I am using it only for charging between batteries, and I can override it with switch/selector if emergency starting of engine is needed (this allows me to use smallest/cheapest Cyrix and to keep charging of both groups in case Cyrix dies for whatever reason and until I change it for a new one). All charging currents and battery group sizes are such that this size of Cyrix is "strong" enough. But, in two years using it flawlessly, I had two occasions burning the 100A (ANL) fuse dedicated for the Cyrix. After analyzing those two rare occasions, the problem is from transients during starting the engine if at the same time AC charger was connected to shore thus keeping the Cyrix closed due to voltage levels on house battery group or if I was restarting the engine while sailing (not connected to shore), but the period between shutdown and restart of engine was not long enough that Cyrix open its contacts due to battery levels and timing profile set in Cyrix. Of course, this does not happen all the time, but only when starting current is extremely high, and that depends of many factors as you know (ambient temperature, at what angle is the engine shaft before starting, etc.) and that is why it has happened only twice for two years. I also do plan to add solar panels and MPPT charger to house battery group side which will make this scenario almost default.
What you need is the right product for the job and the Cyrix-i is not it. This is not due to its amperage carrying capability but rather it's lack of features.
A Blue Sea 7610
SI is rated at 120A continuous (210A for 5 minutes) but if wired PROPERLY, & most of them are not, the relay is physically opened during cranking. This feature is called SI or "start isolation". A feed from your ignition switch opens the relay, during cranking, thus avoiding passing 300A-600A+ across a 120A continuous rated relay. It also minimizes related voltage transients that can occur cranking, especially in poorly wired systems.
The Blue Sea ACR is simply a better choice and is very, very robustly built. I know Wayne K. & Blue Sea spent considerable time working to improve relay contact life to the point that they just don't seem to fail even when wired incorrectly. The 7610SI & the ML-ACR also use very heavy duty 3/8" studs rather than dinky little .25" / M6 studs. The 7610SI is also fully submersible, for as long as 30 minutes, without damage. The Start Isolation (SI) feature of the Blue Sea ACR is really a necessity, especially if your boat has alternative energy etc..
So, I know that only complete and the priciest solution is to change [strike]ACR[/strike] Cyrix for the bigger one (230A countinous current), but that also means different mounting and more space in already tight distribution locker which I have chosen and in which is everything installed and IP protected. And the main idea was also to use the cheapest ACR of high quality which I can easily buy and keep in spare. Next bigger one has the double price.
This will not solve your problem. Even a 230A Cyrix should not be closed during cranking. The minimum fuse size you'd want for cranking a small diesel should be somewhere around 250A, at a minimum. Just last nighty I noted my 583CC Ski-Doo two-stroke / 2 Cylinder engine needing 277A to get the starter turning. Once I replace the bad battery cables, and minimize voltage drop, I fully expect even this tiny little engine will be pulling well over 300A to get the starter turning. In last weeks cold snap, -19F up at camp, the machine did not want to crank very well, even with a brand new AGM. The cranking conductors were dropping 2.2V on top of the normal cold weather battery voltage sag. No wonder it did not want to crank. Snowmobiles suffer similar issues that boats do, in relation to corrosion.
Victron also fails to point out that there needs to be
two fuses, not just one, protecting the paralleling wires, one
within 7" of each battery bank, unless, you're meeting/exceeding the ABYC
exceptions to the 7" rule..
Perhaps Victron wants that 100A fuse to protect the device and hence why they show 100A fuse
at the device end (wrong location).
Blue Sea does not mandate fuse size for the relay and the fuse is simply sized to
protect the wire. Sometimes I will even bump a 7610SI ACR wire GA to 1/0 or 2/0+, complete over-kill for the ACR, in order to utilize the fuses already existing at the battery banks rather than adding more fuses. The short larger gauge wire run is considerably less costly than doing a smaller gauge run and having to add two additional fuses.
With the Cyrix the wire GA you can physically place on an M6 stud is also
limited so cranking current
should not pass through it nor should it pass through a Blue Sea 7610SI ACR, and why Blue Sea adds the SI circuit.
So what do you think of solution, which came to me,
to use the PTC resettable fuse instead of ANL fuse? In that case, I only have to make adapter to mount the PTC fuse in place of ANL fuse. So, even if I get in that situation when cranking the engine, PTC will protect it and reset automatically, so I do not have to change the ANL fuse and the ACR is also protected.
Here is the PTC fuse I have in mind:
BD540 Series - Bladed Devices from Resettable PTCs - Littelfuse
#1 Auto-resetting fuses or circuit breakers are disallowed under the ABYC safety standards so they don't reset into a dead short or reset while a tech or owner is physically trying to figure out what went wrong, when the AC or DC circuit resets and
kills them (AC) or creates an additional short (DC)..
#2 Fuses connected directly to a battery bank should meet the AIC (amperage interrupt current) requirements for the bank size. Generally speaking Class-T (20,000A), MRBF (10,000A) & quality ignition protected ANL's (600A) are the best choices for this. With a properly installed combiner, one with Start Isolation, this will never be a problem. A pair of manually resetting surface mount breakers would be a better choice but most don't meet the AIC so would need a fuse that does closer to the battery.
Do you have some better advice?
Spend the $70.00 - $80.00 on a Blue Seas 7610SI ACR, and wire in the SI circuit, and your problem is solved.
Not all combiners/VSR's are created equal. Victron has some decent products but I am not a fan of the Cyrix-i for the reasons mentioned above.