Poke holes in my wiring plan

[mitiempo]

Originally Posted by sudarkoff

If you go with the bars, make sure to insulate them well. Shorting those by accident (e.g. with a wrench) will be a disaster.

And build the battery box so the batteries cannot move at all - not even one millimeter.

[Captain Graham]

Here is a better drawing of what I would do.

[sailingunity]

Originally Posted by Captain Graham

Here is a better drawing of what I would do.

Well that is a nice schematic!

Just thinking out loud here, but if the start battery is being charged from the house bank via ACR, then any loads on the start battery (e.g. the starter) shouldn't bypass the shunt right? Should the start battery's capacity be included in the total capacity of the battery monitor?

[Captain Graham]

If you wanted to have 2 ways to charge your batteries
1. From the motor
2. From a charger (Solar of shore power)
Here is what I would do.
Yes I have also added a few more power posts and bus bars to make it more modular.
this way the field wiring is separate from the wiring in the battery locker and the electrical panel.

Most of the time wiring problems are in the field wiring not the wiring in the lockers and keeping them separate allows for an easy replacement.

Field wiring
1. Wiring between the 2 lockers
2. Wiring to the loads (lights, nav equipment etc)
3. Wiring to the motor and charger.

[Captain Graham]

Originally Posted by sailingunity

Well that is a nice schematic!

Just thinking out loud here, but if the start battery is being charged from the house bank via ACR, then any loads on the start battery (e.g. the starter) shouldn't bypass the shunt right? Should the start battery's capacity be included in the total capacity of the battery monitor?

Some very good points.
Let me think about it.

[Captain Graham]

Originally Posted by sailingunity

Well that is a nice schematic!

Just thinking out loud here, but if the start battery is being charged from the house bank via ACR, then any loads on the start battery (e.g. the starter) shouldn't bypass the shunt right? Should the start battery's capacity be included in the total capacity of the battery monitor?

Your post made me check how the ACR works.
The ACR is a voltage sensitive switch.
When you are charging the Voltage is high (above 13 volts) the ACR will close connecting the two separate battery banks so all batteries are charged.

When the charging stops the voltage drops to below 12.75 and the ACR switch opens isolating the two battery banks.

The diagram is correct.
See below for more detail

So since the two battery banks are separate except when charging what should you do about your battery monitor
1. since the two battery banks are connected during charging make sure you have a charger that is large enough to charge all the batteries.
2. The big question is do you want to measure the House Batteries, the Starting Battery or both?
I would monitor both by using a selector switch at the battery monitor.

https://www.bluesea.com/resources/1366

What is an ACR?
An ACR parallels (combines) batteries during charging, and isolates them when charging has stopped and after battery voltage has fallen. An ACR is intended to keep a load from discharging both of the batteries.

How does an ACR work?
An ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR′s contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries.

Why do I need an ACR?
An ACR allows two battery banks to be connected so that they can share the output of a single charge source, allowing the user to charge more battery banks than the number of charging outputs. For example, an ACR can be used with a single-output charger, resulting in a simpler system at lower cost than a dual-output charger.

[mitiempo]

Originally Posted by Captain Graham

2. The big question is do you want to measure the House Batteries, the Starting Battery or both?
I would monitor both by using a selector switch at the battery monitor.

That won't work. As soon as you switch to the other bank you will lose bank status - % of full. Monitor the house bank and only concern yourself with voltage of the start battery.

[sailingunity]

Originally Posted by mitiempo

That won't work. As soon as you switch to the other bank you will lose bank status - % of full. Monitor the house bank and only concern yourself with voltage of the start battery.

My concern was that since the start bank is charged from the house bank via ACR, if you didn't include the capacity of the start battery in the overall AH calculation, you'd have what appear to be parasitic losses on your house bank as it is charging the start battery. I could be totally wrong though.

[Captain Graham]

Originally Posted by sailingunity

My concern was that since the start bank is charged from the house bank via ACR, if you didn't include the capacity of the start battery in the overall AH calculation, you'd have what appear to be parasitic losses on your house bank as it is charging the start battery. I could be totally wrong though.

Sorry I guess I did not make myself clear.

The house battery bank does not charge the Starting Battery Bank.
Also the Starting Battery Bank does not charge the house battery bank.

A 12 Volt Marine Battery when fully charged is at 12.7 volts.
Saying it another way a 12 Volt Marine Battery can never be higher then 12.7 volts.

When charging a 12 Volt Marine Battery your charging source need to be higher then 12.7 Volts so it can push the energy into the battery.
Typical charging voltage is about 13.8 Volts.

The ACR is a voltage sensitive switch.
When you are charging the Voltage is high (above 13 volts) the ACR will close connecting the two separate battery banks so all batteries are charged.

When the charging stops the voltage drops to below 12.75 and the ACR switch opens isolating the two battery banks.

I hope this helps.

[mitiempo]

Originally Posted by sailingunity

My concern was that since the start bank is charged from the house bank via ACR, if you didn't include the capacity of the start battery in the overall AH calculation, you'd have what appear to be parasitic losses on your house bank as it is charging the start battery. I could be totally wrong though.

No current can pass through the positive cable - in either direction - without an opposite direction of current through the negative cable. As long as the shunt in the first connection after the negative post all current in or out will be measured.

[sailingunity]

Yes I get that all current will be measured regardless of which battery it comes out of, from an AH counting point of view it will be accurate. But if the AH counter is using total battery capacity as a way of viewing SoC percentage, it seems like it could get thrown off by loads put on the start battery.

Say I have a 100 AH house battery, and a 100 AH start battery. To begin this scenario my start battery is fully charged and my house battery has 30 AH consumed. When I start my engine, I use 3 AH, the shunt picks this up and decrements the house battery capacity 3 AH, while it was actually my start battery that was discharged. My house battery SoC is now off by 3%. Say the alternator pumps 10AH back into the system, assuming an even distribution, my start battery gets 3AH and my house gets 7 AH, meaning now my SoC says 74% charged when in reality I'm 77% charged.

This is an overly simplistic example, and I'm not an electrical engineer, just speculating. In the end I think I would just need to live with using the AH counter as a rough idea, and voltage as a true measure of SoC!

[mitiempo]

Originally Posted by sailingunity

Yes I get that all current will be measured regardless of which battery it comes out of, from an AH counting point of view it will be accurate. But if the AH counter is using total battery capacity as a way of viewing SoC percentage, it seems like it could get thrown off by loads put on the start battery.

Say I have a 100 AH house battery, and a 100 AH start battery. To begin this scenario my start battery is fully charged and my house battery has 30 AH consumed. When I start my engine, I use 3 AH, the shunt picks this up and decrements the house battery capacity 3 AH, while it was actually my start battery that was discharged. My house battery SoC is now off by 3%. Say the alternator pumps 10AH back into the system, assuming an even distribution, my start battery gets 3AH and my house gets 7 AH, meaning now my SoC says 74% charged when in reality I'm 77% charged.

The shunt will not measure what comes out of a battery it is not connected to. Install the shunt on the negative cable from the house battery - first connection after the post. All other negative connections are after the shunt - including the negative of the start battery. The shunt cannot count current from any other battery except the house battery.

See post 52. The switch he suggests to measure both battery banks will not work.

[Captain Graham]

Originally Posted by sailingunity

Yes I get that all current will be measured regardless of which battery it comes out of, from an AH counting point of view it will be accurate. But if the AH counter is using total battery capacity as a way of viewing SoC percentage, it seems like it could get thrown off by loads put on the start battery.

Say I have a 100 AH house battery, and a 100 AH start battery. To begin this scenario my start battery is fully charged and my house battery has 30 AH consumed. When I start my engine, I use 3 AH, the shunt picks this up and decrements the house battery capacity 3 AH, while it was actually my start battery that was discharged. My house battery SoC is now off by 3%. Say the alternator pumps 10AH back into the system, assuming an even distribution, my start battery gets 3AH and my house gets 7 AH, meaning now my SoC says 74% charged when in reality I'm 77% charged.

This is an overly simplistic example, and I'm not an electrical engineer, just speculating. In the end I think I would just need to live with using the AH counter as a rough idea, and voltage as a true measure of SoC!

The issue is that you have 2 independent battery banks and want to monitor both with a single AH Monitor, it will not work.

Either you get 2 AH Monitors or as mitiempo recommended 1 AH monitor for the House Bank and a simple Voltage meter for the starting battery bank.
There is a direct relationship between Voltage and % charged.

When I recommended using a switch on your AH Monitor to monitor both battery banks, I was not thinking correctly, it will not work.

[sailingunity]

I was actually wrong in my previous example. When the alternator kicks in and puts 10% into the bank, even though in reality 3 AH are going into the start bank, the shunt is measuring the 10AH in and giving that all to the house bank. So that would add 10% to the 67%, coming to 77%. It actually winds up being accurate again.

If I put the starter and the start battery after the shunt, those loads won't show up on the AH counter at all, however any charging that goes is all getting seen by the shunt even though in reality it is still getting split. I think that since the starter loads weren't recognized that the charge would wind up being overstated.

Still, starter loads are quite small, and as I understand it an SoC based on amp hours alone is not the most accurate, so I'm sure I'll just have to live with a small amount of inaccuracy.

[sailingunity]

The real issue is not separating the loads, but the charging. I still only have one charge source and this ultimately is the issue. I could use the aux output on the solar charge controllers to help alleviate that, but any charging from the battery charger or alternator could be an issue. Presumably charging from shore power would bring everything up to 100% anyway, so probably no issue there. Charging from alternator - I could put a relay on the ACR to only connect it when the engine is running.