Wednesday, September 15, 2010


When I bought my electric propulsion system for BIANKA back in 2008 I ordered with it a Sevcon 48 volt to 12 volt DC converter.
I never got around to installing it because there was no pressing need.  I have a separate 12 volt house bank on board that provides all the boats 12 volt needs. I forgot about the Sevcon converter.
When I turned my ENGEL cooler into a freezer there was addition drain on the 12 volt battery bank as should be expected.

But, the batteries and solar panels were able to keep up pretty good. But, when I also started to use my laptop too which draws about the same current as the ENGEL in freezer mode (about 2.7 amps) I began to get concerned about draining the batteries. I could run the Honda generator to charge things up. But, I try to minimize it's use as much as possible.
While riding out the gusts of Hurricane Earl I had an energy Epiphany. As the wind gusts from Earl were flowing passed the boat. I noticed that my 48 volt Marine Air-X wind generator was stopped. This was because my 48 volt battery bank for my electric propulsion system was already fully charged and had been for days. I thought what a shame all that wind energy flowing past the boat and I can not use it. Then I remembered the Sevcon converter I had bought.  Ah Ha! I can hook it up and use it to power the laptop from the 48 volt bank and let the regular house bank just handle the freezer and other 12 volt needs.  I took a little while to find Sevcon unit buried in a seldom used locker.

Originally, it was designed to plug into the ASMO Marine controller box via two Anderson Powerpole connectors. But, I was already using those jacks for the solar and wind inputs to the 48 volt battery bank.

What to do?  I really did not want to disconnect the solar and wind generator from the 48 volt bank every time I want to use the converter.  Then in another "Ah Ha" moment I remembered my 48 volt Morningstar Solar controller had a 48 volt tap available. So I took two Anderson Power pole connectors and attached them to the 48 volt output connectors of the Morningstar unit and plugged the Sevcon unit into those connectors.

Now I can run my laptop using the 48 volt solar panels and  wind generator for  energy without worrying about drawing down the 12 volt house bank.  Having more options is one of the added side benefits of electric propulsion that I am appreciating and using more and more as time goes on.


Anonymous said...


Your LAPTOP draws as much current as your FREEZER???

What the heck is wrong with your LAPTOP??

Are you just using the Wall Wart & stepping up to ___VAC, so the brick can drag it back down to the ~9-16vDC most laptops need? This seems silly, but adds an important step -- Power Conditioning.

IFF you are NOT, and you have connected a 12v supply directly to your laptop's DC in port, you won't have to worry about that thirsty laptop much longer! Check your "DC" supply. You may find it to be quite "AC" in its true output. Your "DC-ONLY" motherboard won't appreciate the ripple current!

It would be Most Informative to add an Ammeter to the laptop's supply cable to confirm its actual draw in use.

If you're trying to feed your laptop directly, please be aware that the wall-wart ratings are "worst case"... The following URL seems helpful:

Capt. Mike said...

Nothing wrong with the laptop and no there was no stepping up to AC and then converting it back down to DC. It is what it is. An ammeter was added to the laptop's cord to measure the current draw and it was the same as the Engel freezer. The laptop requires 18.5 volts so there is a power supply involved whether I am using 120 volts from the grid/generator. Or a different power supply if I am using 12 volts. People are often surprised by how much current a laptop can draw. I started tapping into my 48 volt bank because at anchor it was just sitting there and the wind generator was not doing anything because the 48 volt bank was already fully charged. Now at least I am not drawing down the 12 volt house bank anymore than I need to when I use the laptop. I then let the 48 volt wind generator and solar panels top off the 48 volt bank. My 12 volt solar panels then only have to keep up with the demand from the Engel freezer. It's about using ALL the energy resources I have on board.

Me said...

Just curious, Capt. Mike, do you know if it would be possible to use another solar controller using the 48v bank as the incoming power supply (possibly with the SevCon in front to downstep the 48v bank to 12v) to smart charge the 12v house bank from the propulsion bank? This way the solar and turbine can keep the 48v bank topped up while the house bank is using the propulsion bank to keep itself topped up.

Thanks for the info and great blog!

Capt. Mike said...


I'm not sure the SevCon provides enough output voltage to keep the 12 volt batteries fully charged let alone running it through another controller. It may I've just never measured it. I'm just using it to pretty much just power my laptop directly. Though I am thinking about installing it next to the 12 volt house bank to use in case the 12 volt house bank dies. I would then connect the SevCon 48 to 12 volt converter into the 12 volt wiring. But that would be in an emergency. Don't forget there are some losses in the conversion process. I have two twelve 75 watt panels via a solar controller to keep the 12 volt battery bank charged.