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Sunday, 20 March 2016

Electric - Part 3... Availablilty of power.

This whole "electric" topic is boring me now - I'm surprised if anyone is still with me here.... *taps on screen*

The trouble with the topic is that it really is rather vast.  I'm not  even touching the surface with my considerations here but like I've said before, this blog thing is more of a "diary/working notes" production for my own future reference... it's nice to have your  company along the way or course but I'm hoping it will help me when we finally have the boat to work on... as a revision list of things we need to do or consider.

Anyway - this is my final "note" for now on the subject.... possibly ;-)

Right then - Availability of power.

On a boat, the electric you use HAS to come from somewhere when you are not plugged in to shore power.  When the engine is not running, this is from the battery bank.

You may remember, when we placed the order for the boat, we beefed up the standard bank from 440ah to 540ah.  Not a massive increase - a usable 50ah.  I can't recall whether I've waffled on about this before but in simple terms the capacity of the battery bank is NOT it's "usable capacity".  

Actually this isn't true of ALL batteries but given ours will be (this time at any rate) the typical LEAD ACID type, it will be on board Ellis.

Let me explain about "Lead Acid"batteries - It is typically considered wise to use just 30% – 50% of the rated capacity of typical lead acid “Deep Cycle” batteries. This means that a 600 amp hour battery bank in practice only provides, at best, 300 amp hours of real capacity.

If you even occasionally drain the batteries more than this their life will be drastically cut short.

Even if you are going easy on your batteries and are careful to never overly drain them, even the best deep cycle lead acid batteries are typically only good for 500-1000 cycles. If you are frequently going deeper into your battery bank, this could mean that your batteries may need replacement after less than 2 years use.

Given it's unlikely OUR batteries will be the best quality deep cycle ones, you can see why it's important NOT to use too much power before you charge them back up - even then, as the final 20% of lead acid battery capacity can not be “fast” charged. The first 80% can be “Bulk Charged” by a smart three-stage charger quickly (particularly AGM batteries can handle a high bulk charging current), but then the “Absorption” phase begins and the charging current drops off dramatically.

This isn't a big deal if you are charging plugged in overnight, but it is a huge issue if you have to leave your engine running for hours (which can be rather noisy and expensive).so you can easily end up with batteries that never actually get fully charged.

Not fully charging the final few percent would not be much of a problem in practice, if it wasn't for the fact that a failure to regularly fully charge lead acid batteries prematurely ages them - thus reducing the cycles significantly.

SO in our case, we'll only have a "usable" battery capacity of 270ah. It sounded a lot to begin with but when you begin to look at power consumption, it soon gets used up.

Which leads us to a whole other topic for consideration - An ENERGY AUDIT... luckily for you dear reader, I'll save that one for another day - not so much for your sake as mine, as having started looking at it - I'm scared.

Suffice to say - that as I'm more hands on than theory, the photo below provides an insight to where this topic will lead.

When it "warmed up" a little, you can see the reading increased to 

(ignore my right toe please) - 1.71amp - THIS is quite low compared to many appliances... we bought the lowest consumption quoted TV we could find.

AND even on standby, just being plugged in, the 12v TV  (I'll come to that in another post) STILL draws

Oh dear... if you weren't already asleep - I can see the 'Sandman' heading your way... QUICK - hide!

Until next time...

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