12v system rewire including Balmar SG200, ACR, Solar, 1/2/B Switch and On/Off Switch

[dlochner]

I have a positive bus bar just off the maine battery fuse that handles this. If you use the dual post MBRF fuse block note that you are limited to 300 amps total between the two posts in terms of fuse capacity. The SI-ACR is rated for 210 amps intermittent (5 minutes) capacity. So using the battery bank fuse does seem to mean that I am not fully protecting the ACR itself, although I know that Maine Sail endorses this approach.

From Maine Sail's post on ACR's:

"TECH TIP: If you make the “A” & “B” terminal wires for the ACR the same gauge as the house and start bank wiring eg: 2/0 and 2/0 the ACR can share the house and start bank fuses, if so equipped. Start banks are not required to have over-current protection but it never hurts."

See: Making Sense of Automatic Charging Relays - Marine How To

The reason to use 2/0 cable from the battery is to reduce line loss and to provide sufficient capacity to start the motor from the house bank. The actual draw on the cable will be limited by any downstream circuit interrupters. The cable needs a high amperage fuse to support the starter surge. For this reason, in use the MRBT will never see 300 amps continuously unless there is a short in the main cable, at which point you want the fuse to blow, which it should. The other issue is whether the load is continuous or intermittent, or of a short duration. If you were planning to draw 250 to 300 amps from your battery on a continuous basis, then using a dual post would be a poor idea.

Look at the cumulative load on the main circuit, can it exceed 300 amps in use? Most likely not. While the draw on the starter may approach 300 amps for a few milliseconds, there will be no current flowing through the ACR, because there is no charging source.

The ACR does have an intermittent capacity of 215 amps, but that is well below the 300 amp fuse on the battery. The continuous duty rating is 120 amps. What happens if there is 150 amps flowing through the ACR? No fuse will blow and unless the cumulative load exceeds the terminal fuse's capacity, the circuit will not be interrupted.

I suppose that a 120 amp fuse on the starter side would offer protection if the battery side was feed as you propose. That just wouldn't be my choice.

 

[Plumbean]

I'm also curious if it is correct that the dual post MRBF is limited to just 300 Amps total. That would seem to defeat it's purpose, wouldn't it? It doesn't sound right to me.

From the Blue Sea Systems FAQ:

Q:Can each terminal of the 2151 carry a 300 amp fuse?
A: No. The total of the of the entire fuse holder is not to exceed 300 amps.

 

[Plumbean]

The reason to use 2/0 cable from the battery is to reduce line loss and to provide sufficient capacity to start the motor from the house bank. The actual draw on the cable will be limited by any downstream circuit interrupters. The cable needs a high amperage fuse to support the starter surge. For this reason, in use the MRBT will never see 300 amps continuously unless there is a short in the main cable, at which point you want the fuse to blow, which it should. The other issue is whether the load is continuous or intermittent, or of a short duration. If you were planning to draw 250 to 300 amps from your battery on a continuous basis, then using a dual post would be a poor idea.

Look at the cumulative load on the main circuit, can it exceed 300 amps in use? Most likely not. While the draw on the starter may approach 300 amps for a few milliseconds, there will be no current flowing through the ACR, because there is no charging source.

The ACR does have an intermittent capacity of 215 amps, but that is well below the 300 amp fuse on the battery. The continuous duty rating is 120 amps. What happens if there is 150 amps flowing through the ACR? No fuse will blow and unless the cumulative load exceeds the terminal fuse's capacity, the circuit will not be interrupted.

I suppose that a 120 amp fuse on the starter side would offer protection if the battery side was feed as you propose. That just wouldn't be my choice.

Isn't it the case that the fuse is protecting the wire from a battery failure, but the ACR itself will only see amps crossing when it closes the switch because a charge is detected? So those wires being the same as the rest of my main distribution cable (i.e., 2/0) and being protected in the same way, should work, as the ACR itself will never see any current unless it senses a charge. Max charge on my system is a 110 amp alternator.

 

[dlochner]

Isn't it the case that the fuse is protecting the wire from a battery failure, but the ACR itself will only see amps crossing when it closes the switch because a charge is detected? So those wires being the same as the rest of my main distribution cable (i.e., 2/0) and being protected in the same way, should work, as the ACR itself will never see any current unless it senses a charge. Max charge on my system is a 110 amp alternator.

The fuse is protecting the wire from over current, heating up, melting the insulation and catching fire. The ACR does draw current even when it is not open. The circuitry require power, that's why there is a fused ground wire.

What you plan to do will work and is probably safe enough or MS would not have suggested it. Skinnier wire is cheaper and easier to run, so why spend why spend megabucks on 2/0 when you can spend kilobuck on 2?

On my boat, the ACR, Alternator, Charger, Solar and Main DC feed all connect to a single bus bar and each branch is protected by an ANL fuse. The House battery feeds the bus bar. There are only 2 large connections to the battery positive, a parallel cable and a the main cable to the bus bar (there are a couple of sense wires too). The main cable attaches to the battery through a single MRBT with a 250 or 300 amp fuse (can't remember) with a 2/0 cable.

The start/reserve battery has a 2 pole MRBT, one lug to the starter, one to the ACR.

Each bank has its own on/off switch and the whole mess is controlled with a DC+ switch. Each bank can be isolated. The house bank will be charged as long as the switch is on. The start/reserve will be charged even if the on/off switch is off if the house bank is on. If the house bank is off, the start/reserve battery will be charged if the DC+ is in the parallel position. Since the charge sources all feed the same bus bar, it does not matter which source is being used.

 

[dlochner]

I've had a question about this point and thought about another thread, but it does sort of relate ... I used the dual post MRBF for both the house bank and the start bank to connect the positive leads and the ACR leads. Positive leads are 1/0 with 225 Amp fuse and ACR leads are 2 AWG with 150 Amp fuse. Therefore, the ACR leads are connected directly to the batteries. I have DCP selector and On/Off switches to isolate both battery banks. The positive buss that connects positive leads from alternator, shore charger and solar charging is between the On/Off (house bank) and the DCP switches. Therefore, if either On/Off switch is opened, the ACR leads are isolated with the respective battery.

Is this a problem to be corrected? I've noticed that Mainesail's diagram shows the ACR leads connected to the buss with alternator/charger/ solar on the house side and directly to the post on the DCP side of the On/Off switch for the start Batt. If I make either one of the On/Off switches open, than the ACR leads would seem to be isolated, no?

I'm also curious if it is correct that the dual post MRBF is limited to just 300 Amps total. That would seem to defeat it's purpose, wouldn't it? It doesn't sound right to me.

BTW, at the house bank end, I have a 1/0 cable linking the 2 positive posts of the batteries connected directly to one side of the post and the dual MRBF on the other side, connected with a thru bolt. The linking cable is therefore not fuse protected ... is that an issue?

Scott, I think some of the other posts should answer most of your questions, except the last one.

I'm not sure I completely understand how you have cables on the battery connected. I assume you have a couple of batteries in parallel for a house bank, correct?

I have never fused the parallel wires on my house bank, they are however, pretty beefy at 2/0 for the short run. I don't recall ever seeing a suggestion to fuse those cables, unless, perhaps there is a long run between the batteries, but that's a bad idea in and of itself.

 

[Plumbean]

Dave: Your set up sounds very similar to mine. Here is a pic of my set up. This will get mounted next to the battery banks.

- Switch on the top right is to isolate the start/reserve bank. There will be a feed coming out of this to the DC+ switch, which feeds the starter motor.
-- Switch on the bottom right is to isolate the house bank. There will be a feed from the left-side end of the bus bar to the DC+ switch, which then feeds my main DC panel.
- Always on bus bar on the bottom has, from left to right, alternator connection with ANL fuse, charger connection with ANL fuse, and inverter feed with Class T fuse. The waterproof fuse holder underneath the bus bar is for a voltage sense feed for the alternator (Balmar ARS-5 led through an E series battery switch in the engine compartment with AFD)
- My solar controller is currently connected into the feed from the house bank to the DC+ switch in the engine compartment, but I may re-wire it to land it on this panel and feed the busbar directly. Probably doesn't make a difference.
- Switch on the top left is an on/off switch for the inverter

 

[Scott T-Bird]

Scott, I think some of the other posts should answer most of your questions, except the last one.

I'm not sure I completely understand how you have cables on the battery connected. I assume you have a couple of batteries in parallel for a house bank, correct?

I have never fused the parallel wires on my house bank, they are however, pretty beefy at 2/0 for the short run. I don't recall ever seeing a suggestion to fuse those cables, unless, perhaps there is a long run between the batteries, but that's a bad idea in and of itself.

My layout is similar to this except that the ACR leads skip right over the isolation switches and are connected directly to the battery + posts with dual MRBF holders. The way I see it, current generated by alternator or charger will not flow across the ACR and reach either battery bank if my house isolation switch is turned off unless or until I close the emergency/combined switch on DCP. So if my alternator or charger is putting out current, the batteries may not get any current if the house isolation switch is open. Is that right? I could change it easily if it is a bad way to connect them.

You pretty much answered my question about the battery connections. I have 2 4D batts for house bank and the posts are essentially a lug with a hole through the lug - it's a good 1/2" thick and I don't know what the actual term is to describe it. Battery cables are connected by passing a bolt thru the cable lugs and tightening down on the post (lug) with a nut at the other end of the bolt (washers are also used). I attach the parallel cable on one side of the post lug and it is not fused as we discussed. On the other side of the lug, I connect the dual MRBF holder for the Positive lead to the isolation switch and to the ACR. Following the isolation switch, the positive lead feeds the buss and the DCP as shown above.

 

[dlochner]

My layout is similar to this except that the ACR leads skip right over the isolation switches and are connected directly to the battery + posts with dual MRBF holders. The way I see it, current generated by alternator or charger will not flow across the ACR and reach either battery bank if my house isolation switch is turned off unless or until I close the emergency/combined switch on DCP. So if my alternator or charger is putting out current, the batteries may not get any current if the house isolation switch is open. Is that right? I could change it easily if it is a bad way to connect them.

I think your are correct. The ACR needs to be connected to the positive bus bar and the DC+ in the parallel position to charge the start battery if the house is switch is off.

In the drawing you posted, if the start battery switch is off the start battery will not be charged. Attaching the ACR directly to the start battery would allow it to be charged even if the switch is in the off position. Off the top of my head I can't think of a reason to connect the ACR to the switch and not the battery.

The 4d batteries are a back breaker. Why does Catalina want to send their owners to chiropractors?

 

[MikeK2B]

"The start/reserve battery has a 2 pole MRBT, one lug to the starter, one to the ACR."
Question: how do you have the two fuses sized so they don't exceed 300a total?

"Each bank has its own on/off switch and the whole mess is controlled with a DC+ switch. Each bank can be isolated. The house bank will be charged as long as the switch is on. The start/reserve will be charged even if the on/off switch is off if the house bank is on. If the house bank is off, the start/reserve battery will be charged if the DC+ is in the parallel position. Since the charge sources all feed the same bus bar, it does not matter which source is being used."
Question: why does the house bank have to be on for the start/reserve to get a charge? Wouldn't the ACR see voltage from the charging sources hitting the bus bar (i.e. solar, alternator, etc.) regardless of house selector position? If the house is off I don't understand why you would have to parallel the batteries. I know why paralleling would work but I must be misunderstanding the ACR..seems that it needs to see two batteries to share the charge?

I updated my wiring diagram taking into consideration all the comments. Please let me know if it's accurate and any suggestions.
Thanks,
Mike

 

[Ward H]

So if my alternator or charger is putting out current, the batteries may not get any current if the house isolation switch is open. Is that right?

If you mean the reserve battery will not get any current, I believe that is incorrect.
With the house bank disconnected your charge sources will still trigger the ACR to connect the start battery. ACR Spec says after seeing 13.6V for 30 seconds it will connect. If it sees 13V for 90 seconds and it will connect. Since your charge sources should be at or higher than 13V, the ACR will connect and the start battery should still see charging while the house is disconnected.

In the drawing you posted, if the start battery switch is off the start battery will not be charged.

Yes, I agree with this.

Attaching the ACR directly to the start battery would allow it to be charged even if the switch is in the off position. Off the top of my head I can't think of a reason to connect the ACR to the switch and not the battery.

If you bypass the start battery isolation switch and connect the ACR directly to the start battery, you do not have a battery isolation switch.
If the start battery goes bad or shorts, bypassing the switch takes away the ability to isolate the bad battery from your charging sources.

 

[Plumbean]

If you bypass the start battery isolation switch and connect the ACR directly to the start battery, you do not have a battery isolation switch.
If the start battery goes bad or shorts, bypassing the switch takes away the ability to isolate the bad battery from your charging sources.

Agree. This is why I have my ACR wired to the load side of both isolation switches in my set up. Those switches are normally to be kept in the ON position (they will be buried under a settee) and will only be used to isolate a bad bank in order to allow the Dual Circuit Plus switch to either (i) use the house bank to start the engine (if the start bank is bad) or (ii) use the start bank to power the house loads (if the house bank is bad).

 

[dlochner]

"The start/reserve battery has a 2 pole MRBT, one lug to the starter, one to the ACR."
Question: how do you have the two fuses sized so they don't exceed 300a total?

Unless there is a direct short, there will never be more than 300 amps going through the MRBT. Why? The largest draw on the Start/reserve battery is the starter at ~250 a for 2 seconds. When the starter is engaged the ACR interrupts the charging circuit so no current can flow through the ACR cable. This would be the typical case.

In the event the Start/Reserve battery is being used as the house battery (because the house is disconnected), it is protected by several downstream circuit interrupters, a 250 amp slo-blow ANL fuse is the first line of defense. The DC distribution is wire such that all power sources, batteries, solar, alternator, and charger are in parallel. The current provided by these sources would go to the load and if the load was heavy enough it would drop the system voltage down below the combining threshold.

The other limiting factor is the battery itself. It is relatively small (Gap 27) and an FLA, it has a limited capacity to absorb incoming current. Probably about .1C or about 8-10 amps.

As my batteries are set up there just isn't a failure mode that could have the current level exceed 300 amps for any significant amount of time before a CI somewhere in the system opened the circuit.

Question: why does the house bank have to be on for the start/reserve to get a charge? Wouldn't the ACR see voltage from the charging sources hitting the bus bar (i.e. solar, alternator, etc.) regardless of house selector position? If the house is off I don't understand why you would have to parallel the batteries. I know why paralleling would work but I must be misunderstanding the ACR..seems that it needs to see two batteries to share the charge?

In the normal operating condition, the start/reserve bank is not connected to the positive bus bar except through the ACR. The sense wire for all the charging sources are sensing house battery voltage. This tells the devices how much charging current to produce. If the House battery is out of the picture, then no charging current will be produced. With no voltage on the house side, the ACR won't combine.

In the parallel mode, there will be voltage on the busbar and the charging sources will produce current depending on where and how the charger senses the voltage.

 

[dlochner]

If you bypass the start battery isolation switch and connect the ACR directly to the start battery, you do not have a battery isolation switch.
If the start battery goes bad or shorts, bypassing the switch takes away the ability to isolate the bad battery from your charging sources.

The ACR also has a low voltage threshold. If the voltage goes below 9.5v the battery is locked out, effectively isolating it from the rest of the system. I suppose in a belt and suspenders approach adding a switch on the ACR would allow the battery to be completely isolated.

 

[Scott T-Bird]

"The start/reserve battery has a 2 pole MRBT, one lug to the starter, one to the ACR."
Question: how do you have the two fuses sized so they don't exceed 300a total?

The 2 fuses do exceed 300 amps. I have 225 and 150 amp fuses. I haven't been aware of the restriction until now. I had a smaller boat with 75 amp fuses and smaller cables from the ACR. I've used the 225 amp fuses on my boat with the 1/0 cable that came with the boat for 2 seasons and haven't had any problems yet. I'm thinking that I will change out the components this winter.

 

[dlochner]

The 2 fuses do exceed 300 amps. I have 225 and 150 amp fuses. I haven't been aware of the restriction until now. I had a smaller boat with 75 amp fuses and smaller cables from the ACR. I've used the 225 amp fuses on my boat with the 1/0 cable that came with the boat for 2 seasons and haven't had any problems yet. I'm thinking that I will change out the components this winter.

Scott, I wouldn't bother changing the fuses. The probability of exceeding 300 amps is very low. A lower amperage fuse will increase the probability of nuisance trips. Take a look at the trip delay curves for the fuses. The higher amp fuses can carry 100+% of the current with out breaking for up to a minute or more.

A direct short will blow a fuse sized to the wire before anything catches fire and it is very unlikely that both leads would short at the same time. During starting the ACR is disconnected and starting current is very brief.

The 300 amp rating on the MRBT would be especially important on an application that involved high loads for longer durations, such as feeding an inverter. In that case there would be heat build up and subsequent resistance. But for a starter and an ACR, I just don't think it is an issue, the start loads are very short and the ACR loads low.

 

[MikeK2B]

Dave, what are the sizes of each of your fuses on the starter battery?

 

[MikeK2B]

And I guess what I’m getting at is I don’t see what’s wrong with Scott’s install. It doesn’t matter that the two fuses added up to more than 300amp; it’s more that the double pile fuse can’t see more than 300amps across it at
one time, right?

 

[dlochner]

Dave, what are the sizes of each of your fuses on the starter battery?

I can't remember exactly. I believe the starter is a 250 or 300 amp and the ACR a 120 or 150. The ratings can't be read without disconnecting the cables and removing the fuses.

And I guess what I’m getting at is I don’t see what’s wrong with Scott’s install. It doesn’t matter that the two fuses added up to more than 300amp; it’s more that the double pile fuse can’t see more than 300amps across it at
one time, right?

So long as no more than 300 amps continuously passes through the fuse holder all is good. If 301 amps passes through for a brief period, I doubt if anything bad will happen. Take a look at the trip delay curve, if a 300 amp fuse can carry more than 300 amps for almost 2 minutes, then the fuse holder must be able to carry that much too. It would be bad engineering have the fuse holder melt before the fuse blew.

 

[Scott T-Bird]

Scott, I wouldn't bother changing the fuses. The probability of exceeding 300 amps is very low. A lower amperage fuse will increase the probability of nuisance trips. Take a look at the trip delay curves for the fuses. The higher amp fuses can carry 100+% of the current with out breaking for up to a minute or more.

I agree, I don't have any concern about this issue. I was only considering the placement of the ACR cables. Practically speaking, it wouldn't seem to make any difference since the emergency isolation switches are opened, like - never!

 

[jssailem]

Mike.
As I understand your intent is to provide switching that helps you to isolate your power sources.
One of the risks for the owner is the unintentional powering of engine and alternator without a load (battery). When switch conditions that can start the engine yet isolate the alternator from delivering it's power to the battery bank, the unintended frying of the Alternator can occur. It is one of the issues the 1/2/B switch creates. You have a circuit design that appears to cut off the alternator from the battery storage system, yet will allow the alternator to power up.

In a separate issue, yet also associated with system design, MaineSail shows the need to have a safety disconnect on the alternator. When you work on the engine, you need to disconnect the alternator from the battery power. You can do this by installing a switch between the Positive power bar and the alternator. Here is a link to a discussion of this issue.

Balmar MC-614 Alternator Service Disconnect Switch - Marine How To

Incorrectly Wired Service Disconnect Switch This article is part of an on-going series on marine alternators. Our other articles can be found in the link below: MarineHowTo.com Category - Alternators (LINK) Terms used in this article: Alternator B+ = Positive Alternator Output

marinehowto.com

I can see that with an external regulator how you can protect the alternator from self destruction. Not knowing the way your internal alternator regulator is wired I have no comment on it's protection.

It is something to consider as you venture into this project.