Battery switches / isolator

FlyWright said:

Wow! This is exactly what I have on FlyWright. Although my 55A shore charger capacity falls short of CMS recommendations for a 660AH bank, its peak 13A load is the max my Honda eu2000i generator. Iit works well in my fishing and cruising profiles where my Balmar 120A alternator carries most of the charging duties. I feel like my boat electrical system configuration has been validated with an imaginary CMS stamp of approval!

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I felt kinda validated too, although, I am not 100% into his design. And I too am woefully short on charger. 60A for 900+ AH. I am not sure my overall system could support a high-amp charger.

Latest news on my battery charging 'system'! Amazing!

The two 'off, 1, both, 2' battery switches which would appear to be related to the adjacent engine, may well have been once but were not up to last week. Get this; laugh and/or weep: the right switch was wired: stud 1 to the port engine starter (and therefore to the port engine's battery) with AWG 2; stud 2 to the right engine's battery with AWG 2 (it was then connected to the right engine's starter), and an AWG 2 jumper from the output of the right switch over to the left switch. The left switch was then wired with AWG 2 to the house bank. Therefore, with this unlabeled, and apparently-known-only-to-a-PO, arrangement, one could charge the house bank with either engine or with both at the same time.

I was forced to delve into this when the port engine would not start and the left battery switch would turn freely (w/o the customary 'click' to each position). I naturally, but wrongly, decided that the non-start was due to the switch. Turned out that a tank installer had lain on the wire in the ER and physically broke the switch.

I continued my investigation and found that the 'off, 1, both, 2' battery switch at the 12v panel actually had no voltage available for the #2 position. This was easy to discover with the voltmeter on the panel, but hard (still not sure) to follow from within the space under the helm and behind the 12v panel.

I then discovered an AWG 1 conductor, with red tape, curled up disconnected under the starboard engine's battery. I can only surmise that there were once two house battery banks but much of that wiring is missing (I have not yet found an abandoned conductor corresponding to a ground, or any other heavy conductors); I could therefore surmise that each engine could charge its own start battery and a house bank.

Unless I'm truly as dumb as my performance in 'Electricity and Magnetism' at McGill would lead one to believe, I suppose that the battery switches at the engine panels could control which bank of engine+house batteries would start the engines. There would be a lot of unfused large conductors wandering around and there is no sign of any of that remaining.

Means that I now have no way to charge the house bank with either engine. Also means that I'm free to (steal a) design a new system.

Glad you're getting it figured out. The last three used boats I've run all had some very odd-ball wiring for their battery banks. It seems very few really understand what they're doing.

With twin engines, you have a lot of flexibility to KISS. I'm not opposed to battery switches, personally. I find them more simple, understandable and functional than some of the crazy things I've seen done with combiners and isolators.

On my boat the house bank starts one engine, and a dedicated starting battery starts the other. The engine with the house bank has a high-capacity, externally-regulated alternator. But I have switches that allow me to swap these if one alternator fails.

I don't like the idea of combining the house and starting banks for charging. They are likely to be at very different states of charge, and are configured with very different batteries.

On shore power or genset, my 100A charger is connected to the house bank, while the starting and genset banks share a 30A, two-way charger. This way each bank has its own dedicated charging circuit.

Underway both the house and starting banks are charged, or kept topped off, by their respective alternators.

The genset starting bank is only connected to the genset. It's sort of a third back-up to the the other two banks.

This is truly a simple configuration. Normally, I touch none of the switches all season, but in a pinch I have lots of options.

"I don't like the idea of combining the house and starting banks for charging. They are likely to be at very different states of charge, and are configured with very different batteries."

This is true , but it hardly matters.

If the alt is working the out put to even 75% discharged batts will soon be above 12.8 .

At 12.8 the starts voltage will be held and not discharge into the house bank.

At any voltage over 12.8 the starts may be charging a tiny bit to make up for the current used for the start.

No worries , no hassles if there all the same style batt like wet lead acid.

FF said:

"I don't like the idea of combining the house and starting banks for charging. They are likely to be at very different states of charge, and are configured with very different batteries."

This is true , but it hardly matters.

If the alt is working the out put to even 75% discharged batts will soon be above 12.8 .

At 12.8 the starts voltage will be held and not discharge into the house bank.

At any voltage over 12.8 the starts may be charging a tiny bit to make up for the current used for the start.

No worries , no hassles if there all the same style batt like wet lead acid.

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Bingo!!

More batteries on boats are charged in parallel than by any other means. I have start/reserve banks out there that have gone around the planet twice charged in parallel via VSR/Combiner/ACR's for thousands & thousands of hours of charging. So long as charge voltages are the same for each bank parallel charging is basically a non-issue.

Tom.B said:

And that is exactly CMS's point. Why lug around all that dead weight just to start each engine when you can do the same task with less weight and leverage the remaining as a usable house bank?

That is why I was so dumbfounded when I started tracing and discovering the DC system on our relatively new (2000 model) US built boat. It was obviously designed for A) a marina-only boater B) a company that just got 8D batteries by the pallet load. I mean it really made no sense.

If memory serves, it had three 8D banks. Two banks were selected by a 1/2/Off/Both switch to, basically, everywhere. Then there was just an On/Off switch that just added the third bank into the mix. I expected more from them... Oh well. It's all better now.

I don't think I have a layout of the original layout except for maybe a pencil drawing, but I will snoop around and see what I can find and post it.

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I think you would find the original buyers (and the buying market in general) want the 8Ds.

"I've got twin Perkins with a group 31 deep cycle battery for each"

Just wondering why you chose a deep cycle battery to start an engine?

Gp 31 starts are common as dirt , Gp 31 deep cycles are harder to find .

I have completed replacing nearly all the battery wire on our '84 FuHwa with its twin Perkins 6.354s. I used the Blue Seas wiring diagram for three banks, three battery switches and two ACRs. This layout allows me to choose a variety of the battery banks to start the engines, isolates a depleted starting bank, charges the house bank with engine alternators. I have also replaced the 110v battery charger. "Nearly all" means that I have not replaced the anchor winch leads nor the genset leads (both are untinned welding cable).

I have opted to fuse all the battery hots with MRBF post-mounted fuse holders. Adds up to quite a collection since the charger requires three and each lead of an ACR requires one. And I fused the three banks. Total of 9. All the wire is 1/0 AWG except the charger's which is 6 AWG. Capacity of the 1/0 AWG is 285 amps.

I (rather dumbly) installed a 100 amp fuse on the house bank and 200 amp fuses on the starting banks. The 200 amp fuse blew when attempting to start an engine, and adding idiocy to dumpth I proceeded to blow the other two bank's fuses.

I had read that the starter motor ought to draw 160 amps. Apparently not. What size fuses should I now buy (not wishing, at $18. a pop, to experiment)? Easiest answer is to buy 300 amp, which is the largest that's available and overloads the wire a smidge; otherwise 250 which is the next size down.

The starter motor might draw 160 A spinning the engine, but it is typical of starter motors to draw 50-100% more for an instant at stall (right when they engage). If the engine is slow to start, or the battery a bit low, the starter will draw more amps. I'd worry about the reliability of a 250 A fuse if a 200 A blew immediately. Ideally you'd go to bigger wire along with the 300 A fuse, but I'd sleep fine with a 300 A in there anyway.

1/0 seems kind of small for starter cables, even on a small engine. The 2 liter engine on my sailboat is wired with 2/0, the 5.9 liter engine on the powerboat is wired with 4/0 for the start circuit.

DDW said:

1/0 seems kind of small for starter cables, even on a small engine. The 2 liter engine on my sailboat is wired with 2/0, the 5.9 liter engine on the powerboat is wired with 4/0 for the start circuit.

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Interesting re wire sizes. This boat has had the 38mm / 1/0 AWG wire since '84. Our sailboat had 1/0 for its Yanmar 3GM30 and the house bank but the wire size dated (at least) from when the PO had a 100 amp Balmar alternator installed. This boat has the same size house bank as the sailboat(!).

For starting circuit fuses you might need to go higher than the size terminal fuses are available in. As far as fuse cost is concerned, the SAME MRBF (Buss brand) fuses are available at Del City for $7.58.

Ken

So! I popped a 300 amp fuse into the port engines battery fuseholder; got one start out of it and it blew. I've taken the fuse out of the holder and replaced it with a...wait for it...a socket. So, I'm back to as safe as the original system was and, if the socket was ABYC approved, in accordance with ABYC standards.

I run a 300A fuse on my single start battery that starts twin Perkins 4.236s. (My initial 200A fuse blew also.)

kchace, thanks for the tip on the Dell City MRBF fuse deals. Those are great prices.

Well! It's been a long haul. Both engines start and run. And I've removed the sockets and put 300amp fuses in. The engines start and run.

For general info....just read that this is the new ABYC standard (2018) ..


"11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery manufacturer’s short circuit rating or be rated at a minimum of 20kA at 125 VDC or higher."

psneeld said:

For general info....just read that this is the new ABYC standard (2018) ..


"11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery manufacturer’s short circuit rating or be rated at a minimum of 20kA at 125 VDC or higher."

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Interesting. I did a quick check and of common marine fuses I only found class T fuses would meet this spec.


Ken

That is interesting. Nothing in that demands a fuse, though.
Bolted fuses take a bit of time to replace.

psneeld said:

For general info....just read that this is the new ABYC standard (2018) ..


"11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery manufacturer’s short circuit rating or be rated at a minimum of 20kA at 125 VDC or higher."

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I don't even understand what that means. Can anyone translate?

DHeckrotte said:

Well! It's been a long haul. Both engines start and run. And I've removed the sockets and put 300amp fuses in. The engines start and run.

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Great to hear! And the alternators each charge its battery bank??

dhays said:

I don't even understand what that means. Can anyone translate?

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I think that means... don't touch ends of wire with wet fingers having feet in same water as the bulk of wire travels through from its hot-point.

With large battery banks you have enough power to melt down a circuit breaker there by making your circuit protection ineffective. The new standard requires your circuit breaker to not only trip at the correct amperage but to with stand the full onslaught of your battery bank with out failing. If you use components from quality manufacture like Bluesea you probably meet all the standards with out knowing it.

Take wire made by ancor marine. It says right on the wire the gauge and the tempeture. The minimum standard is 80C but anchor wire is built to 105C standard. Most people don’t know about the temperature standard and how it applies but end up safe because of the margin built in by the manufacture. However as one sources cheaper product the first thing that goes is the safety margin.

Keysdisease said:

With all due respect, not all battery switches have alt field disconnects, and few battery switches are wired with alt field disconnects.

While "things" happen, there is no logical reason to turn a battery switch to off with the engine(s) running. Also all popular battery switches are "make before break" which means when switching between 1-2- all the switch never disconnects.

While a nice feature to keep people out of trouble with their alternator, saying any switch with an off position MUST have an alt field disconnect is just not true or current practice. Just don't turn the switch to off with the engine(s) running, there is really no reason to.

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Electrical fire?

"Originally Posted by Keysdisease View Post
With all due respect, not all battery switches have alt field disconnects, and few battery switches are wired with alt field disconnects.

While "things" happen, there is no logical reason to turn a battery switch to off with the engine(s) running. Also all popular battery switches are "make before break" which means when switching between 1-2- all the switch never disconnects.

While a nice feature to keep people out of trouble with their alternator, saying any switch with an off position MUST have an alt field disconnect is just not true or current practice. Just don't turn the switch to off with the engine(s) running, there is really no reason to."

Sugardog said:

Electrical fire?

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That's exactly why I modified my big cable wiring to separate the charge from the load. All alternator charges goes directly to their respective batteries, appropriately fused with large cable, without regard to the HOUSE and START load switches.

If I have an alternator overcharge or short problem that does not get resolved by the fuses, I can turn off the alternator at the start key. The old Perkins engines continue to purr but my hourmeter loses power.

Each bank can be paralleled as needed and plus a charge combiner with ON-AUTO switched at the lower helm. If I lose one engine, the other alternator can run all systems.

If I have a serious short that the fuses do not properly handle, I have separate START and HOUSE switches on the LOAD side that are located outside the ER. These can be switched to OFF within 3 steps of the lower helm.

I patterned the system after airplanes that have similar layouts.

FlyWright, each engine charges its own start batt and, via its own ACR, charges the house bank. If the house bank is sufficiently discharged, the 2 ACRs isolate the 2 start batts. The 110v charger charges each of the three banks through its own fuses. There are MRBFs on each bank so that no hot conductor is unfused. The ACRs are fused as required (each end). Additionally each alternator (now) has its own fuse on its output.

DHeckrotte said:

FlyWright, each engine charges its own start batt and, via its own ACR, charges the house bank. If the house bank is sufficiently discharged, the 2 ACRs isolate the 2 start batts. The 110v charger charges each of the three banks through its own fuses. There are MRBFs on each bank so that no hot conductor is unfused. The ACRs are fused as required (each end). Additionally each alternator (now) has its own fuse on its output.

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Is it a requirement to fuse alt output? If yes why?

L

Lou, Our Perkins were supplied to FuHwa with a fuse in the alt-starter wire, part of the on-engine wiring harness. Of course, that connection at the starter is where the battery is also connected. So it is effectively fusing the alternator to battery connection. When some PO replaced the alternator on the starboard engine, the fuse was removed and that's the wire that melted in my son's miswiring. One of the modes of alternator failure is unregulated charging which would also heat that wire. Another mode of failure is that wire grounding through some fault.


I had the battery-starter wire ground to the engine in my 83 Volvo. Remarkable flames, destroyed the battery and some of the electronics in the car.

"11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery manufacturer’s short circuit rating or be rated at a minimum of 20kA at 125 VDC or higher."

dhays said:

I don't even understand what that means. Can anyone translate?

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Yes, what it basically means if you have a battery bank of 500ah or more, any fuse or circuit breaker on that bank needs to be rated to be able to interrupt a minimum of 20,000Amps at 125V.


The reason for this is because in a really bad short circuit, when the fuse or breaker opens the current "wants" to keep flowing and will create an electrical arc between the two points that just opened - high current can continue to flow between the two OPEN points through this arc. Devices that are rated to be able to interrupt high current flow like this use various methods to "quench" the arc that forms and stop the current flow.


Hope that makes sense.


BTW - a quick check of commonly used marine fuses and breakers - I found no breakers and only "T class" fuses meet this spec.



Ken

Lou_tribal said:

Is it a requirement to fuse alt output? If yes why?

L

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Technically yes, but the fuse goes at the battery end which is the real source of power and is of course available at all times - not just when the alternator is running.


Ken

I'll be honest with you guys... I opted NOT to fuse either of the starter runs, nor the alternator connection to the house bank. Is it wrong and a little dangerous? Yea maybe... even probably, but a blown fuse in either place, for even a minor error, renders the alternator toast or an inability to start the boat. Sure, you can (and probably will) argue that both are better than a fire, and you would be correct, however, I felt like I had to weigh the pros and cons. I may change it in the future, but for now, this is how it is.

kchace said:

"11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery manufacturer’s short circuit rating or be rated at a minimum of 20kA at 125 VDC or higher."





Yes, what it basically means if you have a battery bank of 500ah or more, any fuse or circuit breaker on that bank needs to be rated to be able to interrupt a minimum of 20,000Amps at 125V.


The reason for this is because in a really bad short circuit, when the fuse or breaker opens the current "wants" to keep flowing and will create an electrical arc between the two points that just opened - high current can continue to flow between the two OPEN points through this arc. Devices that are rated to be able to interrupt high current flow like this use various methods to "quench" the arc that forms and stop the current flow.


Hope that makes sense.


BTW - a quick check of commonly used marine fuses and breakers - I found no breakers and only "T class" fuses meet this spec.



Ken

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I spoke with Trojan battery tech and they say the short circuit rating for T-105 golf cart batteries is 2000 amps so if you have the Blue Seas battery terminal fuses, you are OK.

They have a 10000A interupt rating at 14V.