Batteries

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DaveS
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Re: Batteries

Postby DaveS » Thu Feb 05, 2009 6:57 pm

sahona wrote:Bob, if this is the start of what could develop into something else, it's worth remembering that the off/1/both/2 switch may eventually be used purely for choice of OUTPUT from the batteries.
If you subsequently add splitter diodes (Recommended) it won't matter what you do with the switch while the engine is running.
On that same point, in spite of the Westerly manual, the switch is designed as make-before-break, so will only go into 'diode kill mode' if you turn it to "off" with the engine running.
Have fun,

This is not a universal recommendation. Personally I have a deep dislike of splitter diodes (volt drop) and favour the VSR approach, but either way if the circuitry is reorganised so that the 1/both/2 switch no longer switches charging current then I agree that the risk of blowing alternator diodes goes away. I know of no 1/both/2 switches currently made which are designed to be break before make, but I'd still want to check with a meter to see what the switch in question actually does.
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Re: Batteries

Postby aquaplane » Thu Feb 05, 2009 8:03 pm

I have purchased a Hydrometer today to check the batteries when they are in service, I looked at a circuit tester at the same time. I couldn't see much point spending £5 on a circuit tester when a digital multimeter is only £12 to £15 and I can test voltages and continuity with one of them. A mate at work will give me some advice on multimeters, there may even be a redundant one I could borrow.

I wouldn't start moving the 4 way switch without doing some investigation/testing to see just how it works.
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Re: Batteries

Postby Clyde_Wanderer » Thu Feb 05, 2009 11:52 pm

DaveS wrote:This is a subject with about as many opinions as punters, but I'll stick my head above the parapet. In my view (and it will no doubt be challenged) I reckon that the ideal solution would be a high CCA starter battery dedicated to engine cranking and a high Ah deep discharge, traction type battery for domestics. The latter is what milk floats (and, I suspect, older submarines) use / used.

A method of cross-connecting in an emergency is desirable, either by using the "both" position on a 3 way + off switch, a wired-in "emergency parallel" switch (better, since a dead battery can be isolated while using the good one to feed both cranking and domestics), or even a jump lead. The latter suggestion will have doom sayers raising images of hydrogen explosions, but since hydrogen is only given off when batteries are charging - and then only once they're almost "full" - you are unlikely to be in this position and simultaneously trying to make an emergency connection to get the engine started. Unlikely, but not impossible - see later.

Charging more than one battery is another can of worms. My view is that the alternator should initially charge only the cranking battery, preferably using a smart regulator. Once that's fully charged a VSR fitted between the batteries closes, and the domestic battery starts to charge too. That way, accidents apart, the cranking battery should always be fully charged - just like a car battery in fact, reinforcing the point that for starting CCA are more important than Ah. Incidentally, I have a strong dislike of "diode splitters": they're inefficient and they cause all sorts of subtle problems, some of which can easily shorten battery life.

Other charging devices, solar, wind, towed, or whatever, should charge only the domestic battery (because the starting battery should already be nearly full, see above) via a regulator to avoid overcharging unless they're really feeble, e.g. a tiny solar array. A slight sophistication is to have your VSR of "twin sensing" type. This costs little, if any, more than the single sensing type and means that when either battery reaches 13.7V, i.e. is well charged, the VSR closes. This could have advantages on a long engine-free passage in counteracting the self discharge of the cranking battery.

It is the above circumstances which make me think of a possible - if unlikely - scenario where hydrogen could be a danger. If the starter battery died when the domestic was being well charged by wind, say, then there might be a risk in making a connection to it. In these circumstances a minute or so of good ventilation should dispose of any risk.

And what if the big domestic battery dies? Well, that's a bit harder. Using the cranking battery will get you by up to a point, but there's then a real risk of losing the ability to start the engine. There's a lot to be said for having a spare battery - which might have its own job to do in normal circumstancies. I have two: one for the windlass, one for the electric outboard; either could be used as a spare domestic in an emergency.

And I also advocate carrying long jump leads: rafting up to another boat to get a jump start isn't daft, but how many carry the wherewithal to do it?

That's gone on a bit, and if posted on "the other place" would undoubtably generate a long and heated thread, but hope it's of some use.


Reffering to your remarks about diode splitters Dave, I dont like them either as the can create considerable volt drop between alt and batt, but Driftgate do a split charge unit which is electronic and doesent contain diodes, I am using one of them and get something like 0.08 volt dorp, from the X-Split.
I would offer you an excellent (in my and others opinion) diagram for your ideal charging system Nick, but some folk elsewhere think its too complicated, but its not, believe me and it is failsafe.
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Re: Batteries

Postby ash » Fri Feb 06, 2009 1:37 pm

Digital multimeters are handy and cheap. The leads usually give up the ghost fairly quickly. You also need to be aware that as the internal battery ( usually 9V PP3 ) goes done, the voltage readings become inaccurate - usually rising IIRC.

My worry is whether they are accurate - after all 0.1V represents 10% battery capacity. I once made the mistake of 'twiddling' one of the pots when mine wasn't working properly. I've since been able to check and adjust it against an expensive multimeter - both fitted with new internal batteries.

When the leads on mine packed up, I soldered in a twin core flex approx 0.5M long. I fitted a short lead from the 12V negative block with a female bullet connector. The leads on the multimeter are fitted with a female spade connector on the positive to fit the fuseblock, and a male bullet on the negative. I now leave the multimeter permanently connected, so I only need to switch it on to monitor battery or charging voltages.

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Re: Batteries

Postby DaveS » Fri Feb 06, 2009 2:56 pm

Clyde_Wanderer wrote:Driftgate do a split charge unit which is electronic and doesent contain diodes, I am using one of them and get something like 0.08 volt dorp, from the X-Split.


I've seen these advertised, but have never seen a description of what's actually inside the box. Do you know?

Shottky diodes give a much lower volt drop than silicon, about 0.15V rather than 0.7V (I currently have one in my windlass battery charging circuit), but 0.08V seems a bit too good for that. Relays can give a very low volt drop, and I can imagine 2 circuits each sensing the polarity between the common input and an output terminal and switching a relay on when that voltage is positive.

I can't see any advantage of that over the VSR approach, however.
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Re: Batteries

Postby ash » Fri Feb 06, 2009 3:55 pm

DaveS wrote:I've seen these advertised, but have never seen a description of what's actually inside the box. Do you know?


From their website

"Low voltage loss compared with diode splitters which can have a constant loss of 800 - 1000 mV {1 volt worst case} even at float current. The X-SPLIT has a maximum loss of less than 80 mV @ maximum current (for 90 Amp units), dropping to less than 15 mV at float current.
Solid state electronics, no moving parts, no mechanical relay contacts to foul up. "

Driftgate Website

Edit : I've removed a statement which I now feel was wrong.

How good a splitter would be needed for say, 40A alternator, 75AHr domestic, 65AHr (equivilant size) start. Would this cheapy from Maplin be any good? It's only 8A continuous, 20A max. This is a better website.

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Re: Batteries

Postby Clyde_Wanderer » Fri Feb 06, 2009 7:44 pm

DaveS wrote:
Clyde_Wanderer wrote:Driftgate do a split charge unit which is electronic and doesent contain diodes, I am using one of them and get something like 0.08 volt dorp, from the X-Split.


I've seen these advertised, but have never seen a description of what's actually inside the box. Do you know?

Shottky diodes give a much lower volt drop than silicon, about 0.15V rather than 0.7V (I currently have one in my windlass battery charging circuit), but 0.08V seems a bit too good for that. Relays can give a very low volt drop, and I can imagine 2 circuits each sensing the polarity between the common input and an output terminal and switching a relay on when that voltage is positive.

I can't see any advantage of that over the VSR approach, however.


So Dave I have got the 8 to the wrong side of the 0, apolagies, its my Lesdixia :oops: :oops:

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Re: Batteries

Postby DaveS » Fri Feb 06, 2009 9:02 pm

No, your figure of 0.08V is in line with Driftgate's claim of 0.08V to 0.015V. Which is much better than any shottky diode spec that I've seen, so it's presumably not that, and they specifically say no moving parts, so not relays either. Could a conducting FET give a drop as low as that? This is getting to, or beyond, the limit of my knowledge. :?

I'm going on holiday tomorrow with, among others, a pal who designs electronics professionally. I'll see what he thinks... I believe this is termed "phone a friend". :)
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Re: Batteries

Postby sahona » Sun Feb 08, 2009 8:17 pm

Not sure about your "superconducting" diodes, but it's so simple to fool the alternator into delivering the extra 0.6volt that they're not worth the research. A basic regulator won't feed the plates properly anyway - it's not designed to - it's designed to get a car started and run headlamps....
Notice that your car battery lasts a hell of a lot longer than the ones in the boat? - That's partly why, they are purposefully never stretched in a car like they are on board.
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Re: Batteries

Postby aquaplane » Sun Mar 22, 2009 11:55 pm

I've been doing a bit of testing and found that,

With 2 batteries fitted if I switch on the cabin light at the fuse panel and then move the isolator switch from "off" (6 o'clock) to "1" (9 o'clock), the light comes on as the isolator dial passes through 7 o'clock. The light stays on as the isolator is moved to "both" (12 o'clock) and "2" (3 o'clock) and goes out just before getting back to "OFF". So it must be a make before break swich, that's how I want it to work.

Despite taking half a minute of cranking to get the engine going when it's cold, and only running it for about an hour or so, the batterys seem to be hovering about 12.6 volts.

The engine starts first go when it's warm. I'm hopeing the engine will start easier when it warms up a bit, but I will see, it has been chuffing cold the nights before the 3 days I have run it.

I'm not giving the domestic battery much hammer untill I work out how fast/slow I'm draining/charging the two batteries.

I read 14 and a bit volts when the engine is running.

Questions:

Is there a table/graph of volts against state of charge for a battery?

Is 12.6V good/bad/indifferent?

Should I see what happens/ start looking at solar pannels/ forget it and abuse the domestic battery and accept I buy a new one each year?
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Re: Batteries

Postby ash » Mon Mar 23, 2009 12:32 am

aquaplane wrote:I've been doing a bit of testing and found that,

With 2 batteries fitted if I switch on the cabin light at the fuse panel and then move the isolator switch from "off" (6 o'clock) to "1" (9 o'clock), the light comes on as the isolator dial passes through 7 o'clock. The light stays on as the isolator is moved to "both" (12 o'clock) and "2" (3 o'clock) and goes out just before getting back to "OFF". So it must be a make before break swich, that's how I want it to work.


I would agree.

Ash


aquaplane wrote:I've been doing a bit of testing and found that,

Is there a table/graph of volts against state of charge for a battery?

Is 12.6V good/bad/indifferent?



I reckon on (with lead acid battery - and allowed to settle for few hours)

12.7V......100% charged
12.5V........80% charged
12.2V........50% charged

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Re: Batteries

Postby cpedw » Mon Mar 23, 2009 11:14 am

aquaplane wrote:Questions:

Is there a table/graph of volts against state of charge for a battery?



There's a very colourful and authoritative-looking graph here.

Derek

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Re: Batteries

Postby aquaplane » Fri Oct 01, 2010 3:31 pm

Well, 2 seasons on and the batteries are still doing fine, nothing less than you would expect I suppose.

Neither battery gets much use so I usually just put the isolator switch to both when we get to the boat and leave it there 'till we leave.

Now we have started using the Wallas and cabin lights more I just use the domestic battery (2) except when I start the engine when I use battery #1. Depending on how the domestic battery manages the winter use I was thinking of installing a small solar pannel to help out keeping the domestic battery in tip top condition.

I saw this at Maplins http://www.maplin.co.uk/Module.aspx?ModuleNo=223251

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for £12.50, on promo 'till Monday.

Bearing in mind we don't have much in the way of power draw, and no burning desire to install any, I was thinking that maybe it's worth £12.50 to see if it's big enough.

I was going to get a regulator too as I seem to recall that anything bigger than "not very big" needs one.
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Re: Batteries

Postby ash » Sat Oct 02, 2010 6:41 pm

Glad to hear that your batteries have managed to stay charged despite the worry that the alternator wasn't always pulling its weight.

The solar panel might be worth a punt at that price if you can get hold of without further expenditure on delivery / pick-up.

The very best that it could expect to achieve at this time is 0.137 A * 11 Hrs * 30 Days = 45 AHr per month.
What is a more realistic output - 50% ? , 25% ?

Figures for standing losses in a lead acid battery seem to vary - 8% to 40% - less for units with calcium ? to 10% - all per month. 10% of your 110 AHr unit would be 11 for one and 22 for both batteries.

I think that the above figures show that you're unlikely to need a regulator - which would double your expenditure - OTOH peace of mind might be worth the extra £15.

It's your call - resurrect this thread in another 6 months and tell us how it works out.

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Re: Batteries

Postby Arghiro » Sat Oct 02, 2010 7:52 pm

I have something very similar, bought for about a tenner off e-bay. I connect it to one battery directly & that battery is always in fine fettle when I return. One of my batteries is somewhat past its sling-by date (at least one cell is dead) but it will still start the engine if left connected to the solar panel for a few weeks while I am detained ashore.

Go for it - I am considering getting another - one for each battery (as & when I get the new battery).


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