Deep cycle or dual purpose batteries?

[peaman]

I’m not too experienced with 12v systems but have been poking around the E27 battery system lately and the setup for two batteries is the same: direct negative-to-negative connection between the batteries and the positive wires both lead to the selector switch.

it’s not an indication of anything other than precedence but was somewhat wondering the same thing.

it makes some sense - the selector switch sort of acts like a relay allowing the batteries to operate in parallel or individually. If the two ground/negative posts are permanently connected it should still allow the batteries to operate individually or in parallel.

just taking a stab at this since it’s fresh in my mind but would love to be corrected if wrong

Generally, on boats, you will find all negative conductors connected always. So what happens on the +12V side is pretty much all that matters.

Commonly, boats with simple wiring will have a multi-position switch which has an "input" from each battery or battery bank, and which has output to the DC panel. The batteries (or battery banks) may be selected from: None, Bat1, Bat2, Bat1+Bat2. Also, and importantly, the engine alternator output is commonly connected to the "output" terminal of the battery switch.

The common scheme requires that you consider the state of your batteries, and to consider that what comes out (whether for starting the engine or for powering accessories) must be put back in eventually. and it is that awareness that will guide your use of the multi-position battery selector switch. An electronic battery monitor such as THIS ONE can be really useful for keeping you battery banks charged and balanced.

 

[Christian Williams]

+1 for battery monitor such as the Victron above.

Setup calls for a little thought, but worth it. Genius not required.

 

[peaman]

While we're on this subject...(And I apologize profusely if this is Electronics 101 stuff. I'm even reading the 80-pound Nigel Calder book, and I STILL have this question.)

You can see from my photo that there is NOT a direct positive-to-positive connection between the batteries. The positives for both run through the battery switch at the DC panel. There is a negative-to-negative connection for each battery. These are still considered to be "in parallel," correct? I'm having a challenging time finding any mention of this setup and confirming it is considered "in parallel." Every "in parallel" photo I see shows the batteries connected to one another. The 1, 2, Both, Off switch works as expected. I certainly know they're not considered "in series" setup this way. I'm a man that likes confirmation and certainty, so somebody throw me a bone here please.


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Two battery banks are "in parallel" only when the +12V terminals are joined AND the -12V terminals are joined. In the common case that all -12V, or ground connections are joined always, joining the +12V terminals will result in parallel banks. If -12V terminals are joined, but +12V terminals of one bank are disconnected from the +12V terminals of the other bank, the banks are NOT in parallel. In most cases, the un-connected bank will be a dead-end electrically: all voltage and zero current.

To your direct question, Your battery banks are NOT "in parallel" until you set the battery switch to "Both". They are "in parallel" only when each is part of the same complete circuit, and not a dead end.

 

[goldenstate]

A deep-cycle battery means that a battery can be discharged "deeply" without damaging the battery.

A dual-purpose battery means that it is good at providing a lot of power for a short time (like starting an engine, or winching in an anchor rode) and good at providing a little power over a long time (like keeping communications electronics and lights on).

So, without splitting out a starter battery, one would ideally want a battery (or batteries) that could both be deeply-discharged and provide short-burst and long-flow dual purpose energy.

 

[Kenneth K]

To your direct question, Your battery banks are NOT "in parallel" until you set the battery switch to "Both".

That is very likely correct, but not necessarily so.

Another possibility is that each of the side-by-side batteries shown is connected to the same post (#1 or #2) on the back of the switch--which would put them in parallel, regardless of switch position. This would leave room for a second battery/bank to occupy the other, unused post on the switch.

That's why you need to know if there are any other batteries on the boat to be able to answer the question.

 

[bsangs]

Thanks everyone. Whew....Alrighty then.

- These are the only two batteries on the boat.
- I labeled the wires before disconnecting the old batteries so I could be certain I was reconnecting the new ones properly.
- The DC panel is powered when 1, 2 or Both are selected on the battery switch.
- The battery switch is almost always left on Both, though we change that up when anchoring or mooring for multiple days. (It goes back to Both before we start the engine.)
- Both batteries are always charged/charging properly, whether from the alternator, shore power charger, or solar charger.
- Am installing a Victron SmartShunt next month for monitoring purposes, though my solar controller provides some of that information already.

So sounds like only considered "in parallel" when battery switch is on Both.

 

[Kenneth K]

So sounds like only considered "in parallel" when battery switch is on Both.

Yep, that's what is sounds like.

Be aware that while both the Victron and Balmar battery monitors will monitors VOLTAGEs from two batteries/banks, they will only monitor CURRENT (and thus, State-of-Charge) for a single battery/bank.

You will have to decide (by virtue of how you wire your installation) whether to hardwire the two batteries together and monitor current for that entire bank, or, pick one battery or the other to monitor current flows from.

 

[bsangs]

Yep, that's what is sounds like.

Be aware that while both the Victron and Balmar battery monitors will monitors VOLTAGEs from two batteries/banks, they will only monitor CURRENT (and thus, State-of-Charge) for a single battery/bank.

You will have to decide (by virtue of how you wire your installation) whether to hardwire the two batteries together and monitor current for that entire bank, or, pick one battery or the other to monitor current flows from.

Thanks Ken. Very enjoyable, and frequently puzzling, learning all this stuff. I thought it was challenging doing electrical projects in my house, built in 1927 and with much of its original wiring wrapped in some sort of cloth, and about as flexible as a 21st century politician.

If I had these batteries wired "properly" in parallel, does the 1, 2, Both, Off switch even do anything when the alternator isn't charging the batteries? Obviously the Off switch does, but seems to me that if wired in parallel, the system would be pulling from both batteries anyway, regardless of the battery switch being in 1, 2 or Both. (Please, do correct me if I'm wrong.)

 

[Kenneth K]

If you hardwire the two batteries together in parallel, you then only need one positive cable from that bank to the battery switch (say, to post #1).

Now, your boat only has power when #1 or ALL is selected on the switch (but, no reason to use ALL). Selecting #2 won't do anything because nothing will be hooked up to post #2 (except, in your case, you'll have the loose, unused cable which will need to be secured if not removed).

Likewise, your (two-battery) bank will charge from the alternator when #1 or ALL is selected (but, no reason to use ALL). Note: If there is no battery connected to the #2 post and you select #2 with the engine running, you will fry your alternator regulator.

Also note that any time "ALL" is selected, the "loose" cable from the #2 switch post will become hot.

I ideally you would run that "loose" #2 battery cable to a third battery, which is used for reserve/starting in the case that you deplete your main bank.

Really, the only good reason to use "ALL" on the batt switch is to CHARGE two separate banks (i.e., either in your existing configuration, -or-, if you hardwire your existing batteries together and then add a 3rd battery) FROM THE ALTERNATOR. Most shore-power chargers have hard-wired leads to each bank, so selecting ALL is not required. For solar, I guess it depends on how someone wired their system, but people typically want the solar hardwired to the house bank, and then use other means (automatic or manual--including, possibly, the ALL switch position) to power secondary banks when desired.

 

[Kenneth K]

My 1950's house has some of that cloth-covered AC wiring too. It scared me when I first encountered it, but the cloth appears to be just an anti-chafe wrap. All the Insulated covering and interior wiring I encountered appeared to be okay. It is pretty stiff stuff though.

 

[bsangs]

If you hardwire the two batteries together in parallel, you then only need one positive cable from that bank to the battery switch (say, to post #1).

Now, your boat only has power when #1 or ALL is selected on the switch (but, no reason to use ALL). Selecting #2 won't do anything because nothing will be hooked up to post #2 (except, in your case, you'll have the loose, unused cable which will need to be secured if not removed).

Likewise, your (two-battery) bank will charge from the alternator when #1 or ALL is selected (but, no reason to use ALL). Note: If there is no battery connected to the #2 post and you select #2 with the engine running, you will fry your alternator regulator.

Also note that any time "ALL" is selected, the "loose" cable from the #2 switch post will become hot.

I ideally you would run that "loose" #2 battery cable to a third battery, which is used for reserve/starting in the case that you deplete your main bank.

Really, the only good reason to use "ALL" on the batt switch is to CHARGE two separate banks (i.e., either in your existing configuration, -or-, if you hardwire your existing batteries together and then add a 3rd battery) FROM THE ALTERNATOR. Most shore-power chargers have hard-wired leads to each bank, so selecting ALL is not required. For solar, I guess it depends on how someone wired their system, but people typically want the solar hardwired to the house bank, and then use other means (automatic or manual--including, possibly, the ALL switch position) to power secondary banks when desired.

Got it, thanks. I did understand the dynamics of the battery switch with regards to the alternator, shore power and solar chargers, but appreciate the refresher while we're on this topic. And now that I have the "in parallel" confusion ironed out, I think I'm good. No third (starter) battery will be installed. I have a couple of portable jumping batteries always fully charged should an emergency situation arise and I don't have the space - or desire - to add a third battery to this mix. Though who knows, once I install my radar next month, that desire might change. REALLY appreciate all this info you've shared. Just another reason why this forum is truly aces.