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# electric motor conversion for my ski boat. Help!

here is my plan:

- remove big v8 motor from 19 foot ski boat

- install 6 standard size solar panels (40x65) above the boat lift and plug in the boat when not in use.

- 20 kw motor, 96 V, rated current 98A (30-150A), turning 3300 rpm.

- 4 batteries on board each producing 3.4 Kwh 24V. continuous current 110 A.

Questions:

1. Does it sound like the batteries match the power requirement of the motor?

2. Am I correct in assuming the batteries can be wired in series to produce the 96 V?

3. If so, how long would you estimate the batteries will run the motor?

4. Will the 6 panels at about 330w produce about 10 -15 Kw per summer day into the batteries?

Cheers, Bruce.

## Discussions

Thank you for your comments and insight. Sounds like it might work....or it might not.

The weight of the V8 engine is about 600 pounds plus 25 gallons of gas at about 150 pounds. The electric motor weighs in at 130 pounds and the batteries at 300 pounds so I am hoping to lighten the load by about 300 pounds.

Cost is not my biggest concern. I really want to use this project as a demonstration of what is possible with solar power in this context.

I am hoping to use it for an hour or two, then park it and plug it in to the 2 Kw panel array for about 24 hours. If I can only use it every other day, so be it.

https://www.alibaba.com/product-detail/20-kW-high-...

This is the motor I am considering.

Any additional advice is appreciated.

Bruce.

Already enough said here, so I just add my 5 cents on top of it.

Currently available battery types won't allow for any quick charging, are limited in their power delivery and certainly will have more combined weight than your V8.

See it this way:

All the added weight from the batteries needs to be considered.

With 4 big ones it makes up for at least one additional person in the boat, so weight distribution is an issue.

Cables need to be thick, I am talking the thickness of quality jump start cables at least - again weight apart from the costs.

Anything over 48V is something I would not tolerate on my boat as I don't like being electrocuted if something goes wrong with water...

I use a 200W panel to keep a single battery charged and although it is no problem to get it from empty to full on a sunny day I highly doubt 330W will do much for a battery system your size.

Maybe if you use the boat only once a forthnight but then again, what would be fun of using the boat for an hour or two just to run out of juice....

A V8 is undoubtedly over a 100 horsepower..

A 20kw motor is only (20,000/746)=27 horsepower..

Nothing else matters if you want to pull skiers...

You are right. The boat was grossly overpowered (IMO) having a top speed of 100 km/hr and pulling up to 10 skiers at one time.

I am just looking to get it up on plane and pull a tube with a couple of kids. Is there a formula for estimating how much power I will need?

Pic attached.

Cheers.

Well Electric motors can and do deliver five times the rated power 130 HP for short bursts..

That would get you up on plane then the 20kw could keep you going...

If you choose to go this way then you will need a 150 DC volt battery bus, capable of over 600 amperes for 30 seconds, and you will have to provide heavy cooling for the stator windings..

This would also force you to use expensive Lion batteries and the added weight and a control system makes this a difficult control system..

1 hp=746 watts. so let's assume you need a modest 50 Hp outboard to do what you want. (most speed boats I can see at a quick look are 90Hp+)

50Hp x 746watts=37,300 watts That's 37.3 Kw! Thats a LOT of power from a battery.

Not impossible but your not going to do it for less than an outboard costs. + your battery will have a limited life - if electric cars are anything to go by say 2 or 3 years + you will have problems sourcing such a motor I think.

as to how fast you need to go

http://www.ybw.com/forums/archive/index.php/t-1395...

YOur 24 volts x 110 amps=2640 watts. so if the KWh rating is correct you should be able to draw 2.640Kw for slightly over an hour.

Your going to have to serial connect your batteries up to match the 96 volts your motor needs.

On your spec the battery will provide enough current to run the motor for approx 6 minutes. 1/10 of an hour. 2.6Kw / 20Kw

However as watts=Amps x Volts - 30 x 96 is 2.880 K watts and 150 x 96 is 14.400 K watts so something is a little off here.

My array of 16 x 259 watt solar panels produces in theory 4 Kw even on a very sunny day in the UK I get perhaps 2.6 Kw average in summer because they don't track the sun so are only 100% efficient for part of the day. so 1. I cant see yout panels producing 330 watts each. You won't get 15Kw per day (or anywhere close).

Let's look at something comparable for which we can get reall specs.

Your talking about ripping out a V8 gas engine.

The Tesla car used a 581 kW motor

The battery is a 75, or 100 kWhlithium ion

Optional charger: 20 kW from 1ϕ 277 V 72 ASo I guess your spec is somewhat out of the ball park.

It is easy to ask if this is available commercial then it can be done but if it isn't that your probably not the first to think about it but it doesn't work well.