12v or 24v?

[NorthwichTrader]

Should probably put this under a new heading but, Chandlers, who are the best out there for stock and prices? Obviously, Midland get a lot of exposure in the magazines...any other thoughts?

Deals, bargains, for loyal, big-spending customers?

Actually, I'll post it under a new heading, would make better sense!

[MtB]

Broadly speaking, ebay always beats bricks and mortar retailers, MC included.

 

MtB

[NorthwichTrader]

 

With a J3 you don't need a starter motor at all!

 

MtB

 

P.S. I have 24v starter on Aldebaran, 24v alternator, 12v domestic system and a 24v to 12v step-down device to charge the 12v domesic batts from the 24v alternator

Sounds interesting, and a possibility!

 

I've got to get something done with the insides of the compression chambers before I start firing petrol in them! They could really do with some kind of internal shot blasting to totally rid them of rust, and I'm guessing some kind of enamelling? Two of them also have a cracked foot! They are the next job on the list, though I'm not quite sure how to proceed, yet?

[MtB]

Ah I assumed yer J3 was a runner. I'd cut your losses and flog it then and buy something cheap to run and fix. BMC1800 for example. You'll be quids in on the deal! Even a dead J3 seems to be worth £3k and you'll get as good BMC 1800 for £600.

 

Kevin Whittle has a dead J3 on ebay at the mo. Or maybe its a J2 £5k BIN IIRC!

 

MtB

[smileypete]

I disagree. It's not just the cost but the availability. 12v water pump failed? On the shelf in Midland Chandlers. 24v pump failed? Fat chance, a two week wait to order one and twice the price I bet. Same story with everything else. You HAVE to think ahead and keeps spares in stock for EVERYTHING, which means buying twice, in effect.

It's not that bad, ASAP and similar have them off the shelf:

 

http://www.asap-supplies.com/marine/water-pressure-pumps-24v/shurflo-fresh-water-pressure-pump-509507

 

It's often something in the the pump head that goes, so you could also buy an identical 12V one and swap the pump head over.

 

OK if you're so good at doing that kind of stuff or planning ahead then 12V is the way to go. A lot of the off shore brigade have 24V boats and it's not problem for them.

 

cheers, Pete.

~smpt~

[Paul C]

If you're going to build the boat so that a single failure is so critical that you NEED a part that day or the next, then it may be an important issue for you. But you can take precautions and plan around it. For example we have about 10l of bottled water in case the water pump (or any other critical part of the water system, for that matter) fails. That would be enough to get to a water point and fill up with another 10l, then get a bigger temporary water container and fix the water pump (or other issue) at our leisure.

[matty40s]

The solar issue is not really an issue. Most of the panels I have fitted are 24v or 36v and need a mppt controller to make best use if the voltages produced whether a 12 or 24v system.

For example, an array of 2 x 200w+ panels connected can be producing 90v plus on a good day-so even a 24v system would need a decent regulator.

[smileypete]

The solar issue is not really an issue. Most of the panels I have fitted are 24v or 36v and need a mppt controller to make best use if the voltages produced whether a 12 or 24v system.

For example, an array of 2 x 200w+ panels connected can be producing 90v plus on a good day-so even a 24v system would need a decent regulator.

With a 24V bank there's also the option of using the cheaper ~60p/watt 36V domestic panels with a half decent PWM controller, which won't work out for a 12V bank.

 

The £140 saved on buying a 20A PWM instead of a 40A MPPT could then buy quite a bit more solar and/or put towards better batts.

 

cheers, Pete.

~smpt~

Edited July 1, 2013 by smileypete

[matty40s]

Depends if you are paying silly prices for your mppt controllers.

[Charlotte Burnett]

On chandlers, your local one probably has a "fit out scheme" where you give them money for credit and then get a big discount. Many will at least match web prices on such a scheme although sometimes you might need to have a chat and you will also be able to use them for advice on parts and installation, a friendly cup of tea when you are in tears that something won't work and perhaps the odd use of a delivery address and loading wharf when you need to dangle a washing machine through an improbably sized hatch.

[smileypete]

Depends if you are paying silly prices for your mppt controllers.

40A MPPT from Bimble solar for £180, not that silly for a UK supplied one, know any better?

 

Even if using MPPT on 24V it could still halve the MPPT cost, as say only a 20A MPPT would be needed for 24V instead of a 40A MPPT on 12V.

 

cheers, Pete.

~smpt~

Edited July 1, 2013 by smileypete

[fudd]

Have I misunderstood something. I thought that 24 v stuff drew less ( roughly half ) the ah that yer common 12 v system did. Would that not mean less charging time? Or am I just thick or misinformed?

[Paul C]

Have I misunderstood something. I thought that 24 v stuff drew less ( roughly half ) the ah that yer common 12 v system did. Would that not mean less charging time? Or am I just thick or misinformed?

 

It would mean half the charging time if there were double the batteries.

 

Another way of looking at it:

 

One might use, say, 2x 110AH 12V batteries in a 12V system --> total energy capacity would be 2 x 110 x 12 = 2640 W.h. (2.64 kWh to get us to a recognisable unit and multiplier).

 

And in comparison, a 24V battery bank might use 2x 110AH batteries (2x 12V batteries in series). The same current flows through each of these batteries, by the time its gotten through the first battery the voltage is 12V, when it leaves the 2nd one its now at 24V. Instead of 220AH (which is only a measure of energy at one given voltage - 12V) of batteries - lets say it another way, instead of the batteries being able to supply 220A for 1 hour, they would only be able to supply 110A for an hour - the difference being that them 110A are being supplied at 24V! Same amount of energy but half the current, double the voltage.

 

Confused or ok with that?

[fudd]

 

It would mean half the charging time if there were double the batteries.

 

Another way of looking at it:

 

One might use, say, 2x 110AH 12V batteries in a 12V system --> total energy capacity would be 2 x 110 x 12 = 2640 W.h. (2.64 kWh to get us to a recognisable unit and multiplier).

 

And in comparison, a 24V battery bank might use 2x 110AH batteries (2x 12V batteries in series). The same current flows through each of these batteries, by the time its gotten through the first battery the voltage is 12V, when it leaves the 2nd one its now at 24V. Instead of 220AH (which is only a measure of energy at one given voltage - 12V) of batteries - lets say it another way, instead of the batteries being able to supply 220A for 1 hour, they would only be able to supply 110A for an hour - the difference being that them 110A are being supplied at 24V! Same amount of energy but half the current, double the voltage.

 

Confused or ok with that?

I think I've got it. I just didn't realise that you needed double the amount of batteries.

Ta.

[Paul C]

You don't....because the current required by everything, for the same power, is halved.

[fudd]

 

You don't....because the current required by everything, for the same power, is halved.

 

But I thought 24 v would halve the charging regime.

[madcat]

I would fit a 24v alternator to charge the start batteries and fit a second large 12v alternator to charge the domestic batteries. Two alternators is not an uncommon thing on boats. If you put the headlamp on the 24v system then make sure it cannot be left on if the engine isn't running and flatten the start batteries.

[Paul C]

 

You don't....because the current required by everything, for the same power, is halved.

 

But I thought 24 v would halve the charging regime.

 

Why?

[fudd]

You don't....because the current required by everything, for the same power, is halved.

I do if I want to halve the charging time. You said so.

 

Why?

Because I thought 24 v stuff used half the ah. Then the batteries would discharge in half the time

[Paul C]

I do if I want to halve the charging time. You said so.

Because I thought 24 v stuff used half the ah. Then the batteries would discharge in half the time

 

Have a look at post #38 again.

 

Let's take a possible scenario, you have 2x domestic batteries connected in parallel for a 12V domestic boat electrical system. You wish to convert to 24V. Are you going to add 2 more batteries, or rearrange the existing pair into series (to give the required voltage, 24V)?

 

Also, you mention charging, you can't charge a 24V battery bank with a 12V charger. Say you already had a 12V 20A charger, are you going to replace it with a 24V 10A charger or a 24V 20A charger?

[fudd]

 

Have a look at post #38 again.

 

Let's take a possible scenario, you have 2x domestic batteries connected in parallel for a 12V domestic boat electrical system. You wish to convert to 24V. Are you going to add 2 more batteries, or rearrange the existing pair into series (to give the required voltage, 24V)?

 

Also, you mention charging, you can't charge a 24V battery bank with a 12V charger. Say you already had a 12V 20A charger, are you going to replace it with a 24V 10A charger or a 24V 20A charger?

Sorry Paul. I haven't explained things very well.

All I meant t say was if a 24 v item used half the ah then the batteries would last twice as long before needing charging. Not realising that you need twice the batteries to achieve this. I just thought, stupidly that 24 v was more efficient.

Steve P

[fudd]

So if I bought 4 t 105s and wired them for 24 v what capacity would they have?

Steve P

[Paul C]

So if I bought 4 t 105s and wired them for 24 v what capacity would they have?

Steve P

 

They're 6V batteries, so they'd need to be all in series, the capacity expressed in Ah would be 225 but at 24V! Ah is only a useful unit of capacity if the voltage is also defined.

 

5.4kWh is a more meaningful way to express the energy they store. P = V x I.

[fudd]

 

They're 6V batteries, so they'd need to be all in series, the capacity expressed in Ah would be 225 but at 24V! Ah is only a useful unit of capacity if the voltage is also defined.

 

5.4kWh is a more meaningful way to express the energy they store. P = V x I.

Right then.

A 24 volt fridge would run for twice as long as a 225 ah bank of 12 v batteries with a 12 v fridge

Steve P

[Timleech]

Right then.

A 24 volt fridge would run for twice as long as a 225 ah bank of 12 v batteries with a 12 v fridge

Steve P

 

Yes, but the bank of batteries would be twice the size for the same Ah capacity.

 

Tim