A watermaker for £150?

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paul

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If you're crossing the pond and don't have a watermaker why not buy a dehumidifier and inverter. Soak a towel in seawater, hange it infrontof the dehumidifier. You should get at least 2 litres a day. Not quite as much as a watermaker of course, but a lot cheaper and keeps the boat dry too!
 
Yes. They draw about 15amps an hour which equates to about 60amps per litre made. That's about 90mins running if you have a decent alternator with a Sterling or adverc attached.
 
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Yes. They draw about 15amps an hour which equates to about 60amps per litre made. That's about 90mins running if you have a decent alternator with a Sterling or adverc attached.

[/ QUOTE ]

To be helpful I will try to translate this into standard units so that others can perhaps follow:

"They draw 15A and take 4 hours to produce 1 litre, i.e. consuming 60Ah. To replace this with an alternator delivering 40A will take 90 minutes."

Apologies if I appear overly pedantic, but there are sound reasons for adopting unambiguous international measurement units to describe physical phenomena, and introducing fictitious units such as "amps per hour" helps nobody. The fact that howlers of this sort can often be seen perpetrated by so-called "technical" contributers to yottie mags etc. does nothing for their or their publications' image.

I say nothing one way or the other as to the merits of the actual idea. FWIW I've installed a (much smaller) dehumidifier wired up so that it only comes on when the engine is running or I'm connected to shore power, but its sole purpose is to help keep the boat dry. In my normal cruising area I tend not to suffer from water shortages. /forums/images/graemlins/smile.gif Apart from a small amount used for battery top-up, the water produced by the dehumidifier normally goes down the sink!
 
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To be helpful I will try to translate this into standard units so that others can perhaps follow:.......

[/ QUOTE ]I said something pretty similar on one of the forums here around 18 months ago and was attacked by (regular and otherwise very credible experienced) posters who insisted that 'amps per hour' is a bona fide unit! It took nearly 48 hours for someone to come to the rescue and support me.

I shall be watching with interest to see whether the 'amps per hour' brigade will join in.

Now, as for the dehumidifier-watermaker, I think if you take into account the space and cost of the equipment and fuel and compare that with carrying bottled water for an entire ocean crossing, the bottled water will win without serious contest. You need to ask how much fuel the engine would be using while providing the power to run the dehumidifier and recharge the batteries. Between one and two litres per hour, I suspect. So 90 mins running will probably use three litres of fuel to make a couple of litres of water under perfect conditions (actually I think that's a huge over-estimate but never mind). That's not a good trade. Running my watermaker under similar conditions (i.e. from batteries and recharging with a diesel generator for one hour with the generator running at low load), we use one litre which is less than a main engine as it is quite a small efficient engine with direct drive to the generator, not a belt drive. This makes 40 litres of fresh water direct and puts around 60Ah net usable into the batteries (I have an 80A charger). The watermaker draws 20A so the recharge would run the watermaker for three hours, i.e. giving another 120 litres of water. in total my one litre of diesel makes around 180 litres of water. Actually, I mostly run the watermaker from the solar panels but even running it from diesel is not much more expensive than taking water from some marinas in the Med.
 
Thankyou.

A long time ago I made a similar correction and was generally derided as a pedant.

I believe that they reflect fundamental misunderstandings and it is helpful to clarify them.
 
[ QUOTE ]

To be helpful I will try to translate this into standard units so that others can perhaps follow:

"They draw 15A and take 4 hours to produce 1 litre, i.e. consuming 60Ah. To replace this with an alternator delivering 40A will take 90 minutes."

Apologies if I appear overly pedantic, but there are sound reasons for adopting unambiguous international measurement units to describe physical phenomena, and introducing fictitious units such as "amps per hour" helps nobody.

[/ QUOTE ]

Supported!

Perhaps it's time for someone with time and interest to produce a list of "proper" units.

We recently had EPIRBS transmitting in Hz.
 
While the pedants are right, don't lose sight of the perfectly acceptable description of batteries as storing so many amp-hours and we have all seen mAh on rechargeable batteries.

Try a variant.

Yes. They will take about 15Ah from a battery which equates to about 60Ah per litre made. That's about 90mins running to recharge if you have a decent alternator with a Sterling or adverc attached.

Makes sense to me, I often think in terms of Ah taken from battery capacity and its a pretty standard way of computing battery needs when setting up or adding new equipment.

Fireproof suit now donned:-)
 
[ QUOTE ]
While the pedants are right, don't lose sight of the perfectly acceptable description of batteries as storing so many amp-hours and we have all seen mAh on rechargeable batteries.

[/ QUOTE ]That's all absolutely fine. 'amp-hours' is perfectly good shorthand for 'Ampere hours' and means exactly the same thing, no problem.

[ QUOTE ]
Try a variant.

[/ QUOTE ]Oh dear! /forums/images/graemlins/smile.gif

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They will take about 15Ah from a battery....

[/ QUOTE ]No! In the example given, they "take about 15 Amperes, or A" NOT Ah, which is Ampere hours. There is a huge difference. It's the same sort of difference as the difference between miles and miles per hour.
 
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We recently had EPIRBS transmitting in Hz.

[/ QUOTE ]Which, of course, they don't. Let's see what people think the answer is....
 
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[ QUOTE ]
We recently had EPIRBS transmitting in Hz.

[/ QUOTE ]Which, of course, they don't. Let's see what people think the answer is....

[/ QUOTE ]

Errrm, yes they do. Just an inconveniently large number of Hz.
 
Amps per hour is a reasonable unit (but not how it is usually mistakenly used). It's rate of change of electrical charge flow, i.e. Coulombs per second per second (requiring a big numerical factor too).

For example, my battery when fully charged was delivering 20 Amps. 3 hours later it was getting a bit flat, and could only produce 14 Amps. Therefore the rate of change of current was 2 Amps per hour.

Now I'm also being pedantic. I shall go back to sleep.
 
That's not a 'unit' (certainly not in any standarised, universally understood sense). It's merely an expression, a form of words. Of course there's nothing inherently wrong with that, except that by no means everyone would use it or understand it in the way you use it -- precisely why we have agreed international units.
 
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That's not a 'unit' (certainly not in any standarised, universally understood sense). It's merely an expression, a form of words. Of course there's nothing inherently wrong with that, except that by no means everyone would use it or understand it in the way you use it -- precisely why we have agreed international units.

[/ QUOTE ] If you are going to lecture on correct use of units you should get your facts straight first. A/h or Ah^(-1) - which would quite reasonably be read "amps per hour" are legitiamite units as the previous poster described just for a rather obscure application describing the rate of change of a current.

It is a UNIT in a universally understood sense and any decent science (and presumably engineering) graduate would recognise its true meaning and should be able to derive the correct unit (or the correct "meaning" for a unit) using Quantity Calculus.

The original pedant is of course correct in pointing out that Amps per hour is incorrect in this instance and that Ah would be more correct.
 
Well I understood what was meant. Though technically meaningless (Probably a design engineer /forums/images/graemlins/laugh.gif).

It's the epirb drift that made me laugh. I agree with Benbow, of course its frequency is measured in Hz. K, M or T are just multipliers. How many people express thier earnings in K's instead of pounds per year?

What does throw me a bit are the poll results.

[ QUOTE ]
I think that EPIRBS transmit in....
Users may choose only one (26 total votes)
MHz
15 58%

Watts
1 4%

Kilometers
2 8%

English
3 12%

I don't understand the question or none of the above
5 19%



[/ QUOTE ]

"%" erm?


Dave.
 
I agree with you, A/h is a perfectly suitable unit for describing rate of change of current (or ROCOC as it used to be abbreviated to when I was a student, which for some reason always caused a smutty chuckle...)

Should the answer in your example not be -2A/h though?
 
Wonderful stuff.

As a sailor , I just look for the 80 or 110 on a battery

Don't really care whether they are lumps, bananas or amp hours.

As long as its battery shaped and the bloke selling does not look too dodgy, I'm willing to take the risk!

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
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