An interesting use of two 1,2,BOTH switches tied together

You may have seen a setup like this before, it was new to me when I purchased the boat. I thought it clever enough share with the forum.

The boat has a 6 golf car battery house bank and a single 8D for starting both main engines. The house bank and start batt each have their own 1,2,BOTH switch. The two switches are tied together on the #1 post.

Rod on Marine HowTo has a good article on 1,2,BOTH switches 1,2,BOTH Battery Switch Considerations where he talks about too often the way the switch is wired there is not true isolation, the idea of using the house bank to start engines if it's large enough and keeping a start batt / bank in reserve.

This two switch configuration address these issues. Have a look at the circuitry and a usage placard I've generated and posted at the switches.

Using the "Start" switch alone the operator can select between the two most useful modes:
- House Bank does it all keeping the start batt in reserve
or
- Total isolation of house bank and start batt

Using both switches the operator can also
- Combine the batteries
or
- Run all from the start batt

It is worth noting the PO ran the alternator outputs directly to the batteries reducing the risk of breaking the connection with engine(s) running and blowing the alternator.

This set up does not meet Rod's concept of keeping it simple and easy to reduce human error. It requires an understanding of the wiring or at least a willingness to read the usage placard before turning switches.

In my mind, that's a horrid and confusing way to wire that with 2 switches.

It should be wired as "1" being the start bank and "2", being the house bank on each switch (or the other way around). So normally you leave the engine switch on "1" and the house switch on "2" to use the banks for their normal purposes. But you can switch house power to the start bank if needed or switch starting power to the house bank (or both). But in normal use you don't touch the switches.

This set up is probably 30 years old. It made sense back in the 80’s. Once the Echo Charger, Smart ACR and the DC to DC charger showed up it failed to be a complete solution. The complication with this system is directing the charging source efficiently and preventing human error.

rslifkin said:

In my mind, that's a horrid and confusing way to wire that with 2 switches.

It should be wired as "1" being the start bank and "2", being the house bank on each switch (or the other way around). So normally you leave the engine switch on "1" and the house switch on "2" to use the banks for their normal purposes. But you can switch house power to the start bank if needed or switch starting power to the house bank (or both). But in normal use you don't touch the switches.

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rslifkin. Yes, your method would be less confusing.

tiltrider1 said:

This set up is probably 30 years old. It made sense back in the 80’s. Once the Echo Charger, Smart ACR and the DC to DC charger showed up it failed to be a complete solution. The complication with this system is directing the charging source efficiently and preventing human error.

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tiltrider1. Agree. This system is old and needs re-work. Including upgrading the OEM 55 Amp internally regulated alternators to larger externally regulated alternators and tied together with the Balmar Centerfielder or the Wakespeed WS500 to the house bank. Then Echo Charger, Smart ACR or DC to DC charger to charge the start batt.

To both, thanks for the replies and input. As I stated in my original post I'd not seen this setup before and thought it pretty clever. Though it did cause some head scratching before I used the switches.

Don’t like the house bank ALWAYS tied to the start bank through that black line. If the house fails it will drag down the start bank

High Wire said:

Don’t like the house bank ALWAYS tied to the start bank through that black line. If the house fails it will drag down the start bank

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Grounds being always tied together like that is normal (and doesn't carry a risk of one bank killing another).

It also depends what the switch is feeding . So depending where the DC panel is fed and where the starter is fed could easily change how you use the 1,2,both,off switch.

My opinion is ant system has to use more than just one switch, but not necessarily two 1,2 both,off switches

rslifkin said:

Grounds being always tied together like that is normal (and doesn't carry a risk of one bank killing another).

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Ok. No other negatives shown.

Agreed on the multiple switches being needed in any good setup. For my setup with 2 engines, a generator and house, I've got 4 switches. 1-2-both-off for each engine and the generator (to select starting power to either of the 2 start banks) and an on/off for house power. Only link in my setup between house and start power is a pair of ACRs. In normal ops, none of the switches get touched. They're on there to re-configure power sources in an abnormal situation.

rslifkin said:

Agreed on the multiple switches being needed in any good setup. For my setup with 2 engines, a generator and house, I've got 4 switches. 1-2-both-off for each engine and the generator (to select starting power to either of the 2 start banks) and an on/off for house power. Only link in my setup between house and start power is a pair of ACRs. In normal ops, none of the switches get touched. They're on there to re-configure power sources in an abnormal situation.

Click to expand...

Though my system is different from yours I have a similar switch management approach. Normal is the 6 golf car bank serving as house and start. The start batt sits in reserve fully charged. No need to touch the switches. All of the other combinations are to address abnormal situations.

Regarding using a house bank as a start bank Rod at Marine HowTo in his article addresses that. Personal experience verifies it. On our last cruise we drained the house bank to 50%, in other words full 'normal' discharge. It still started the mains.

This idea harkens back to a comment that Northern Spy mentioned in another thread. It was along the lines of “the perfect is the enemy of the good”.

On my sailboat I came up with a system that used the existing 1,2,Both and On/Off switch’s to convert the original 2 battery system to a House and Start system. Doing something similar I was wired so I could start from either the start or house bank, all charging sources went to House bank with an echo charger feeing the start battery.

Yeah, it was odd and would not be familiar to someone unfamiliar with the boat, but it allowed being able to run the house load and start the motor even if one or the other battery failed.

It wasn’t perfect, but it was good and didn’t require me to spend bucks different switches.