Electric narrowboat

Not long after setting off this morning we met Arabia, a shortened 1907 Josher. And very nice it looked.

We have seen a few boats called Black Swan; this is the first real black swan I can recall seeing.

It was at Horninglow Basin, where we'd stopped for water and Elsan.

We saw our friends Chris and Joy on Wrens Nest at Willington, so we tied up and Jan went for a cup of tea on their boat while I cycled back to Branston for the car. On the way I stopped to talk to the owner of this boat, which appears to be called Ovaltine but which doesn't appear in the boat listing. Neither does the registration number. (To the right it says "Bob up & down".)

Anyway, Ken was very happy to talk about his boat which has an interesting drive train. The clue is in the signwriting: "Drink delicious Ovaltine for an electric experience"(!) This is what caught my eye as we cruised past. Yes, the boat is electric, in that the propeller is driven by an electric motor. Where there would normally be an engine there is a large diesel generator; where there would normally be a gearbox is the electric motor driving the prop shaft via a belt with a 3:1 reduction achieved by the size of the pulleys. There are four crates of lithium ion batteries, each crate not much bigger than a conventional lead-acid battery. The batteries are what are used in electric cars. The motor runs on 110VDC. Ken runs the generator, a "site generator" only while the boat is stationary and only for about three hours a day. He cruises on battery power with just a faint whine as the only noise in addition to the prop wash. Ken has installed a multiplicity of meters to monitor voltage, current, amp-hours and temperature. And probably a few other things which I didn't notice. I'm afraid I can't remember the amp-hour capacity of the battery bank, nor the power of the motor - although I think the generator is capable of 5kW and the motor might be similarly rated. The motor, by the way, looked fairly insignificant, certainly compared with the vast generator. One thing which surprised me was the almost complete lack of solar panels on the roof. Apparently they would have introduced too much extra complexity to the charging system.

I'm sorry I didn't take any photos "under the bonnet". I suppose I didn't want to intrude. I'd never make an ace reporter.

Thank you, Ken, for taking the time to talk to me about it all.

Keeping with the electric theme, after I dropped the car off at Swarkestone, my route back to Willington took me past the former power station's old cooling towers. A notice states that permission was being sought for their demolition between January 2017 and July 2017.

Well, they are still there, still dominating the landscape. I think they should remain. The power station itself seems to have been reduced to a few lumps of concrete.

Rudder balance and galvanic isolation

Part one of the boat survey has been completed. On Saturday the hull was inspected and tested for thickness. Some pitting was found to a depth of 1.5mm in the hull sides (nominally 6mm). The surveyor thinks this is galvanic corrosion caused by being hooked up to mains electricity for long periods. The boat's current owner (no pun intended) was there welding on new anodes, so he filled some of the pits with weld (so the surveyor reports). I hope this is an acceptable treatment!

I had been particularly concerned to get the surveyor's opinion of the rudder. When we road tested the boat I found the steering heavy, and I wondered if the rudder balance was out, i.e. whether there was not enough of the rudder forward of the pivot point. The surveyor took a photo of the rudder for me, from which I estimate that the ratio is about 15% forward and 85% aft of the pivot point. This seems to be close to what is usually the case, and the surveyor suggested that experimentation with a longer tiller arm should be done before thinking about adding more steel to the leading edge of the rudder.

So that's reassuring!

As far as the corrosion is concerned, I'll make sure that galvanic isolation is in place before the boat is installed in the marina for Ally and Ben.

I've been investigating so-called galvanic isolation. This is the means of interrupting the mains earth as it tries to come on the boat via the shore line. Obviously an earth path is still required for mains fault conditions, but a continuous earth bond between boat and land can set up an earth loop, and small but corrosive currents can flow in the water, eating away at exposed metal. Sacrificial anodes are there to take this corrosion current on the chin, as it were, and prevent the rest of the boat corroding.

There are two common ways of providing this break in the earth line and still keeping things safe. One is by using an isolation transformer where mains current is allowed through, but the earth link is broken. The other is by using a "galvanic isolator", which is, I believe, the more common method on narrowboats. A galvanic isolator is a very simple piece of electronics. It usually comprises two diodes in series, in parallel with two more diodes in series but "facing" the other direction. The forward voltage drop across a conducting silicon diode is about 0.7V, so two in series gives about 1.4V. If a fault condition occurs, if, say, the live wire on board touches the metalwork of the boat, the conducting diodes will provide little resistance and the mains earth will be restored. But at voltages below about 1.4V the diodes will present a very high resistance. And the damaging "galvanic" currents are, I'm told, a result of voltages below this figure.

Now, these diodes have to be able to handle the maximum current which the shore line can supply. If they blew (went open circuit) then no earth protection would remain - obviously dangerous. So commercially available galvanic isolators are rated at 70A and above. Hence the heatsink, but I think £70 is a lot for four diodes!

An isolation transformer will provide complete earth isolation, but I need to do more thinking about the earth protection side of things. I've just spent an hour searching for isolation transformers on the internet. The best I could find was a 1kVA transformer from CPC at £150. But this wouldn't be big enough. No wonder the diode devices are more popular!

LED dimmer circuit

Using the circuit from the Renewable Energy UK website I breadboarded an LED dimmer. Again, if I could draw a circuit diagram on the computer I would.

I used just one "string" of three LEDs with a 140 ohm resistor in series. Apart from the 555 timer IC (59p (I think) from Maplin) all the components came from my drawers (ooer, missus). It worked extremely well: the LEDs not dimming completely, as predicted, but at "full" brightness they looked bright enough.

Measuring the voltage at "full" I found:

10.2V across the three LEDs in series, i.e. 3.4V across each LED.

And a lot less power was consumed by the electronics - I used a (small) BC546 transistor which didn't even get warm.

An interesting side effect of taking the photo: when pointing the digital camera at the LEDs the camera's CCD sensor shows you the mark/space ratio on the screen!

There's more to do, as I now want to combine the voltage regulator with the dimmer.

LM317T voltage regulator

I breadboarded a voltage regulator using the LM317T (69p from Maplin) and various reclaimed components. The aim was to power one of the Poundland "Camping Lights" in its original all-the-LEDs-in-parallel form. The breadboard is a bit of a mess as to the right is a simple zener diode and two transistor voltage regulator; to the left are various old projects which I couldn't be bothered to remove. Using two fixed resistors and a variable resistor between them, with the slider connected to "Adj" on the LM317T, I achieved an output voltage of between 2.1V and 4.4V, exactly what I wanted to feed the LEDs.

I took a few measurements of current and voltage applied to the 24 ultrabright LEDs in parallel:

3.0V across LEDs; 0.13A drawn (power = 0.39W)
3.5V across LEDs; 0.70A drawn (power = 2.45W)
4.0V across LEDs; 1.43A drawn (power = 5.72W)

Any less than 3V and the LEDs weren't bright enough; any more than 4V and I was worried that they'd burn out. As it was, with 4V across them the LM317T was getting very hot, even with the (admittedly small) heatsink. It's rated at 1.5A, so it was running close to the limit.

If I knew how to draw circuit diagrams on the 'pooter I'd draw it.

In the next post I'll describe the LED dimmer I built (from the excellent Renewable Energy UK website).

LEDs and voltage regulation

I'm continuing to play with LEDs and electronics (see previous post on this). The idea is to build something which will accept a nominal 12V supply and regulate it to power LED light units. I've been using the LM317T regulator and experimenting with various voltages feeding the LEDs. Progress is slow because there's a lot of gardening to do at this time of year: I need it to rain so I can stay indoors and experiment more!

I'll post more on this.

more on LEDs

I found the Renewable Energy UK website today (while searching for voltage regulator circuits). It had exactly the information I was looking for, as I wanted to use a solar panel to charge a small 12V lead acid battery. The website has lots of useful stuff on LEDs; and 12V batteries being charged from solar panels. Highly relevant to boating methinks.

LED lights

In a comment on an earlier post Brian from NB Harnser asked for some more details on some LED lights that I'd discovered.


new light unit and modified unit

The lights I'd bought were from Poundland and can be seen here. The packaging reads: "Outdoor Solutions LED Camping Light". The first one I bought was last year just before a camping trip to the Netherlands. It lit up our large tent a treat. The units take four AA batteries. Inside there are four curved printed circuit boards, each with six white LEDs connected in parallel; each circuit board connected in parallel. There's also a switch, and a hook for hanging it in your tent, or you can slide it over a patio umbrella pole.

I suggested that they would be easy to convert to 12V use, just by arranging two pairs of circuit boards in series, so there would still be 6V across each LED. When I did this, and connected it across my car battery, several of the LEDs immediately burned out.

Oops!

I think I know why this happened. When I first investigated these lights I was surprised to see all the LEDs connected in parallel, as the usual voltage across an LED is just 2V. There is 6V of battery power, from four 1.5V AA cells, in the unadulterated unit. But the actual voltage across the LEDs while battery powered I measured to be only just above 3V. At the time I assumed my batteries were a bit low, but perhaps it's because the LEDs draw so much current (say 20mA each, times 24 gives almost half an amp) that the internal resistance of the batteries limits the current. And anyway, you're not supposed to put more than 2V across an LED - that's why they usually have current limiting resistors in series. Not in this cheapo unit, though!


modified unit - each circuit board wired in series with the next (switch taken out of circuit here)

What I did next, to another unit, was to connect each of the four groups of six LEDs in series, so the voltage across each LED should now be only about 3V. This is a very simple mod, and it worked perfectly. I don't yet know how it will cope with alternator charging voltage of 14.7V. When I connected my modified unit across 12.8V car battery it took 73mA (i.e. consuming just under 1W); when the engine was running the voltage was 13.6V and the unit drew 134mA (i.e. nearly 2W). This suggests that the light unit is quite sensitive to fluctuations in input voltage. A simple transistor regulator would probably be a good idea, or, even simpler, a series resistor. I'm going to have to try this after dark: comparing unmodified battery unit with modified one across car battery.


showing how easy it is to modify: just snip off one lead and reposition the other so as to connect outside edge of one board to inside edge of next

A word of warning though - I've found several of the Poundland units with very dodgy soldering. The last one I opened up had the no solder at all joining the links between each AA battery position. And the previous one had some dry joints at the LEDs.

There's a discussion of LED lighting for boats on the OwnerShips discussion forum here.