Can batteries be wired in series AND parallel? - SailNet Community
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Can batteries be wired in series AND parallel?

What I am imagining, but my brain can't quite grasp, is if you can wire up your standard house bank of 12v batteries to ALSO supply a 24V supply for a windlass.

For example:

House bank = 2x 12V group 27 batteries wired in series to supply 12v to the house.

Can these 2 batteries also be used with parallel wiring to supply the 24v windlass?

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Old 07-08-2014
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Re: Can batteries be wired in series AND parallel?

IN series to raise voltage TO 24 volts

In PARALLEL for more amp hours

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Old 07-08-2014
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Re: Can batteries be wired in series AND parallel?

Hi the basic rule for batteries in parallel is that the voltage will be the same as what the batteries are rated at so eg if I had 5 12v batteries in parallel I would have 12 volts output , but if I had 5 12v batteries in series this would be 5 x 12v =60v
Note when you wire batteries in series make sure you go from negative terminal on one battery to positive terminal on another battery and so on
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Re: Can batteries be wired in series AND parallel?

Highway trucks have a series parallel switch on them to run their 24 volt starters momentarily off a 12 volt system.

Ray
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Re: Can batteries be wired in series AND parallel?

Quote:
Originally Posted by erps View Post
Highway trucks have a series parallel switch on them to run their 24 volt starters momentarily off a 12 volt system.
Could that be safely done for as long as it takes to power a windlass. Any idea how that would be wired?

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Re: Can batteries be wired in series AND parallel?

Needs a bunch of solenoids to disconnect the parallel and connect the series . Every 24v truck starter has this setup. Or.. It can be done with a second battery with neg to the main pos.and pos only to the winch (The winch neg goes to the main neg) and a completely separate charger to keep it up. If you don't get this right the smell of burning insulation will be the first clue.
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Old 07-08-2014
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Re: Can batteries be wired in series AND parallel?

Yes, it could be done, most likely with a set of relays but I wouldn't recommend it. You would have to ensure nothing was ever connected directly to the battery terminals to ensure 12V devices never see the 24V and you would have to switch the ground wires from the battery, as well.

Let's call the battery that isn't switched "B1" and the one that is being switched from parallel to series "B2". Normal 12V operation would have the B2+ connected to B1+ and B2- connected to B1-, i.e. in parallel providing additional amp hours to the 12V system.

To run the windlass at 24V, the relays would have to disconnect the B2+ from the B1+ and then connect it to the + wire of the windlass. The relays would also have to disconnect the B2- from the B1- and instead connect it to the B1+, i.e. in series to provide the 24V to the windlass. While doing this, you would have to guarantee the B2 battery isn't connected to anything else in the system.

If, for example, the B2- terminal wasn't disconnected from the boat ground system, when the relay connects it to the B1+ terminal to put it in series, it would also provide a direct short between the B1+ and ground.

By the same token, if the B2+ terminal wasn't totally disconnected from all of the other boat systems, when it was put in series, those boat systems would also see 24V.

You would also have to ensure the switching was done properly so that all disconnections were done before the new connections were made (break before make).

It's been a long time since I looked at power relays so this functionality may be available in a double-pole/double-throw break-before-make relay. If so, it wouldn't be that hard to implement.

I think it would be very non-standard, though, and it would be easy for someone in the future to not understand what was being done, bypass the relay to directly wire something to the second battery and cause all kinds of interesting effects.

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Re: Can batteries be wired in series AND parallel?

Quote:
Originally Posted by MedSailor View Post
Could that be safely done for as long as it takes to power a windlass. Any idea how that would be wired?
The easiest way to achieve this is to use two '1-off-2' battery changeover switches (not the normal 'off-1-2' ones) - the traditional system actually used two knife switches - but you do need to know what you're doing to operate it.

Basically, you connect two batteries in series (24VDC) - one positive terminal to one negative - and wire the "1" position of each switch to the batteries negatives and the "2" position to the positives. Putting both switches in the "1" position or the "2" position gives you 12VDC from either Batt#1 or Batt#2 respectively and "1"&"2" either gives you 24VDC or nothing.

Supposedly one upside to this is that if your batteries are dead flat, switching the system to 24V might allow you to start the engine (or fry your starter if you judged it wrong), so.. is it safe?? Hmmm..

Anyway, if I was in your position, I'd be installing a completely separate 12VDC "winch battery" with the negative connected to the bus side of your Main Switch and the positive going directly to the winch breaker. For better usage, you could call it your "reserve battery" and wire the bilge pump, etc. off it without needing a whole extra breaker panel.

EDIT: Was typing this when CChaos responded above. I think we're saying the same thing, just this system is manual, his is automatic.. not sure... but my recommendation still holds.

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Last edited by Classic30; 07-08-2014 at 10:27 PM.
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Old 07-09-2014
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Re: Can batteries be wired in series AND parallel?

Quote:
Originally Posted by MedSailor View Post
What I am imagining, but my brain can't quite grasp, is if you can wire up your standard house bank of 12v batteries to ALSO supply a 24V supply for a windlass.

For example:

House bank = 2x 12V group 27 batteries wired in series to supply 12v to the house.

Can these 2 batteries also be used with parallel wiring to supply the 24v windlass?

MedSailor
First you mixed the two
Series is to increase the Voltage, Parallel to increase the Ah

Do you have any 24V installations already?

What is the reason for this question
install a new anchor windlass?

The benefit of installing a 24V windlass is that you can use thinner cables for the same wattage, assuming two similar windlass'es of 1000W
1000/24= 42amp
1000/12= 84amp

But as have been already explained (in other replays), you cant have the batteries wired both ways at the same time.
If you have 12 volt charging this would turn the charging off while you use the windlass.

assuming that you currently have 12V only, I would say that you should stick to that.

There are other ways to feed a hungry windlass
-Install correct sized cables
-But a dedicated battery close to the windlass and charge this through thinner cables

If you already have a mixed 12/24 Volt installation you have other options.
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Re: Can batteries be wired in series AND parallel?

Quote:
Highway trucks have a series parallel switch on them to run their 24 volt starters momentarily off a 12 volt system.

Quote:
Could that be safely done for as long as it takes to power a windlass. Any idea how that would be wired?
It's been a long time since I worked on trucks, but the switch was a single solenoid switch that activated when the starter was activated. It supplied 24 volts to the starter. What I don't remember is whether the electric in the cab still got 12 volts or whether it got a shot of 24. I don't remember the lights in the cab getting really bright. I think the rest of the truck remained 12 volts.

Ray
S.V. Nikko
1983 Fraser 41
La Conner, WA

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