I'm looking for some help with my latest project. I'm building a 32 foot trimaran and want to power it with a electric motor. I looking at either a Etek or Perm motor run at 48 volt. I would probably use a Sevcon controller with regen capabilities. My concerns is in two categories. First is in regen mode, what stops the batteries from being over charged. I assume that the controller cuts the connection to the batteries but what protects the motor from producing current if it is still free-wheeling. Second is the use of a generator for extended cruising under power. Being a 48 volt system what would be the best way to charge the batteries. The biggest marine generator is 24 volt at 200 amp. Would this still charge the batteries. I have a line on a 7 hp Kubota diesel which I plan to use to power the generator. Could I use a second Etek/Perm motor as a generator (how to protect the batteries)? What about using a switching relay to connect the generator directly to the drive motor.
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Support V is for Voltage
No, a 24 volt generator would not charge a 48 volt battery pack. Instead the 48 volt battery pack would do damage to the 24 volt generator. Please let us know how large the explosion is. Better yet make a movie and post it on youtube for us to see.
Andrew made a good analogy about voltage which I'll try to repeat. You can think of voltage as a tall cylinder filled with water. A 48 volt pack is twice as tall as a 24 volt pack. If one were to take two cylinders, one 48 feet tall the other 24 feet tall, and connect them together, the water from the 48 foot tall cylinder would rush into the 24 foot tall cylinder until the two are of equal height.
You could get 2 24 volt generators, connect one to the first two batteries, the other to the second two batteries.
I've hung around marinas and know there are a wide range of electricity generating gizmos. Solar panels and wind turbines are available suitable for sailboat use.
I'm looking on westmarine.com.. AirBreeze 12V Wind Generator (and there's a 24v version) Sunsei Flex Flexible Solar Panels ... solarpanels would be interesting because even though each is 12v you can string them in series to make a 48v set.
I don't know how you would protect the batteries from too much regen, I've never heard of that consideration. Ah, but it occurs to me, it's really difficult to create a situation where you'll recover more energy from regen than you expended getting to the point where you're recovering power from regen. It's essentially a perpetual motion machine problem. Take the typical situation.. you have a car w/ regen, you start driving, you brake for a light, and recover energy through regen. You will have expended energy getting to speed, and then you recover some during the stop. If you were to recover more energy stopping than you spent getting to speed, there would be a net gain and would lead to a perpetual motion arrangement. Okay, so you could say, oh, the car is at the top of a hill and you regen all the way down. But what about when you drive back to the top of the hill? Nobody's drive is downhill all the way.
I am having a hard time imagining how regen would work in a sailboat. There's no brakes. Where do you expect to get regen? Or do you intend to anchor the boat in some current, and use the propeller to drive the motor to make it act as a generator? That would actually be rather interesting to try and is an atypical regen situation.
Sunsei Charge Controllers That's meant to work in combo with a solar panel. It appears these are geared to a 12v battery pack and 12v panel. So four panels and four charge controllers?
Another way is to separate times you're charging from times you're using the pack to drive the motor. You configure the pack as 12v while charging and configure it as 48v while driving.
Another thing to think about is even though the etek is capable of 48v or higher it will run at 24v just fine.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
I know my comments have come a little late but. It is not impossible to charge in 24volt and operate an etek in 48 volt. But why not have the option of running the etek at 24v low speed and 48volt for high speed. I have solved the problem on my boat by putting a on of on toggle on my console that controlls which voltage I am running. For the motor I have two 24 volt banks set up two batteries in series in each bank. To make this work correctly I use three contactors. They are used too combine the two banks parallel with two solenoids when the toggle switch is at the bottom on position (24v or low). For the high or 48 volt connect the two 24v banks in series with a single contactor. So in otherwords when the generator is operationg keep the switch set to the low toggle setting or yes fireworks. Infinate wisdom does not only include the norm. Check out a dual voltage starting switch at JC Whitney it works similar although is only for 12 to 24 volt.
This guy needs to run a potentometer for his brake regen on a kelley controller or a pmac millipak to turn on, down or off depending how much regen he is getting. If he is on a live aboard sailboat using a charge controler such as tristar 45 or xantrex 45 (originaly for solar or wind) in diersion mode or a battery bank diversion control to heat water for showers is a good way to use up extra energy. If it is a racing boat use the extra power to ventalate the hull with a 24 volt fan when it comes on and he is sailing he will realise it and can adjust the pentometer.