Just an electric update

Nothing of real news here, but a few might be interested:

Since 2000 my Columbia 36 has had DC electric auxiliary propulsion. The system is a 72 Volt system using simple lead-acid batteries, a golf cart motor, and a 300 W bank of solar panels. System works great for us, we've gone from Vancouver to Mexico, plus a few hundred miles on the Atlantic coast before we realized we MUCH prefer the Pacific.

The latest upgrade is that I have added a temperature gauge. It is interesting to see the equilibrium temperature on the motor - it seems to max out around 50C. We haven't had any hot summer days yet, so I don't know how much this is affected by the air temp. The motor is, of course, below the waterline and thus relatively cooled by the seawater on the hull, but still the motor room becomes quite warm. I have installed a bilge blower to get additional fresh air into the motor room..again, too early to report the impact.

This summer's cruise is a planned eight weeks out on the Pacific Coast of Vancouver Island. Fingers crossed: "Cruise" & "Plan" are only loosely connected.

Fair winds to all hands.

Chris McKesson

 

Looking forward to the results.

 

Yes, it works, but how good? Numbers would help tell. You went from Vancouver to Mexico using just this system? What is the range on a full charge. How long to recharge? Did you use auxiliary power?

 

Happy to provide numbers Sam, which ones would you like?

No, we didn't motor to Mexico, we sailed. The electric drive is only the ship's AUXILIARY propulsion - her primary drive remains Dacron. But it gets us in and out of harbour, over the bar, through the rapids, and home when we're becalmed.

My range on battery is about ten miles. I store 10 kWh of energy in a bank of six lead-acid batteries, and drawing on that bank at ~3kW will drive the boat ~3 knots for ~3 hours = ~10 miles. I do also have a Honda gasolene-fueled generator on board and I can extend range by running as a gasolene yacht. I try to avoid this, with the result that our typical gasolene consumption is about ten gallons per year. (For the numbers, 10 gallons of gasolene is about 125 kWh out of the generator.)

Time to recharge depends also upon multiple factors. If I'm in a marina it's simply overnight using shore power. If at anchor, well again the arithmetic is simple: A 10 kWh battery bank being filled by a 300W solar array... Of course, if I have engaged a lot of hotel loads at the same time, then some part of the solar power is going to house loads and not to recharging. And sometimes the sun don't shine...

You asked "Sure it works, but how well?" That is, of course, a subjective question. It works well enough for my wife and I. We enjoy the silence. We enjoy the lack of maintenance. We put up with a low speed-under-power and a short range.

Other owners will have other preferences.

All the best,

Chris McKesson

 

The silence would be nice.

 

Good to see a shout for the lead acid batteries and simple things in life. If you read anything on battery power these days its all about super efficient read expensive storage. It clearly has its place where space, range and performance is at a premium, but here we have someone with an effective, usable and affordable system that does the job. Personally I prefer clockwork.

 

Temperature is a real killer in DC systems. It is just sucking up your amps. If you could improve cooling, perhaps via passive heat sinks. Aluminum works great for this. You might see improvement in range.

 

As a result of electrical loss (mainly the resistance of copper windings) there is a raise in temperature. With improved cooling you do nothing to improve efficiency.

Only cooling of the solar array can provide some gain in performance because the output is temperature dependent, but in this case that doesn't really matter: a 10% increase is just 30 watts!

 

Are you sure?

CDK, would not keeping the motor, battery, and even cabling cooler help then be less resistant.? It would also help life spam.

 

No, I'm afraid it doesn't help a bit. The OP says the motor temp is around 50 C, which is quite acceptable. For the batteries it is a bit high but I don't know where they are located.
Copper resistance is 1.68 x(10-8) ohms at 20C, the temp coefficient is .00386 % per degree C so the loss at 50C is just 0.11% higher.

 

You may be right but you killed what I learned in school. I thought that it as go hotter resistance would increase eventually getting to a critical level and then eventually melting the copper. Perhaps at 50C this not an issue yet. I also think that batteries lose ability to charge when temperature increases therefore many chargers have temperature sensors.

I also know that solar panels take a big hit on performance too.

 

I wonder how difficult it would be to make your own lead acid batteries.

 

CDK is right.
At 50°C the increase of resistivity of copper is negligible.

What you have been taught in school is that the power transformed into heat by a conductor is given by the formula Pth = R I^2.
If this power can be dissipated to a cooling medium, then the conductor reaches some equilibrium internal temperature.
If the power Pth cannot be dissipated, then the heat will build up inside the volume of the conductor. The temperature of the conductor will then rise until it melts the insulation first, and then the copper too.

 

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http://www.westmarine.com/buy/maste...sic-e-propulsion-system--11419769?recordNum=6