I need some help!

Boats, Jet Skis, Kayaks etc., including hovercrafts
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ble2k   10 µW

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I need some help!

Post by ble2k » Aug 21 2014 8:18am

Hello together,
first sorry for my not perfect english.

I have an old Valmet Terhi 5PS outboard, and removed the gasoline engine. The connection of the two shafts would not be a problem for me.

I search a 24v 1500 - 2000 Watt motor continuous power. Or is it to much? The old gasoline engine has rotated at 4500-5000rpm.
Can you help me to find the right motor?

Thank you
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Valmet Terhi 5PS
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parajared   10 kW

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Re: I need some help!

Post by parajared » Aug 21 2014 9:54am

The Motor Rpms and hp are helpful to know. 5hp is 3500 watts. Electric motors are rated in KV so for a motor that spins at 5000 rpm you would want something to the tune of a 66volt pack that has enough energy to kick out 60 amps and a paired to a 75 kv motor.

If want to go 24 volts you would need something to the tune of a 200kv motor that can handle 150 amps. I believe golf cart motors do this.

My recommendation would to be to go for the higher voltages (and thus lower amps) to keep the stress on the controller, wires and battery low.

ble2k   10 µW

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Re: I need some help!

Post by ble2k » Aug 21 2014 10:04am

parajared wrote:The Motor Rpms and hp are helpful to know. 5hp is 3500 watts. Electric motors are rated in KV so for a motor that spins at 5000 rpm you would want something to the tune of a 66volt pack that has enough energy to kick out 60 amps and a paired to a 75 kv motor.

If want to go 24 volts you would need something to the tune of a 200kv motor that can handle 150 amps. I believe golf cart motors do this.

My recommendation would to be to go for the higher voltages (and thus lower amps) to keep the stress on the controller, wires and battery low.
i think 1500watt is enough power, i don't need the same power as the old gasoline engine, i want to drive 6-8kn

John in CR   100 GW

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Re: I need some help!

Post by John in CR » Aug 24 2014 10:30am

ble2k wrote:i think 1500watt is enough power, i don't need the same power as the old gasoline engine, i want to drive 6-8kn
That depends 100% on the hull. A catamaran designer I was working with to adapt his sailing hulls to electric primary came up with 1500W for cruising at 7knots. That was a 30ft cat with fine lines. I forget the displacement we were looking at. OTOH an inflatable dingy with just 1 or 2 people aboard probably couldn't get close to 7knots on just 1500W.

ble2k   10 µW

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Re: I need some help!

Post by ble2k » Aug 24 2014 3:51pm

the boat is an 14ft picton, my problem is to find a electric motor with 24v 1,5 to 2 kw, brushed or brushless? whats better?

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parajared   10 kW

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Re: I need some help!

Post by parajared » Aug 25 2014 10:28am

Brushless is better because the "brushes" don't wear out and less energy is lost to heat, however brushed motors are generally cheaper and require less elaborate (read expensive) speed controllers.

ble2k   10 µW

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Re: I need some help!

Post by ble2k » Aug 25 2014 11:46am

parajared wrote:Brushless is better because the "brushes" don't wear out and less energy is lost to heat, however brushed motors are generally cheaper and require less elaborate (read expensive) speed controllers.
do you have any idea which brushless motor (+controller) at 24volt 1500-2000 watt continuous power perform?

manufacturer and model?

thanks

blisspacket   100 W

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Re: I need some help!

Post by blisspacket » Aug 25 2014 4:02pm

Operating the brushless motor requires a strong ESC -- Electronic Speed Control. At the same time you shop for the motor, shop for the controller. AND... some controllers require sensors mounted in the motors. There is a bewildering array out there, and they all cost $$$. And sometimes you can fry an ESC in seconds, adios $80 and up. Spend long hours reading many threads on EndlessSphere, and you'll begin to understand.

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parajared   10 kW

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Re: I need some help!

Post by parajared » Aug 26 2014 9:50am

I imagine you could just toss a cheapie hobbyking esc + motor in the thing and be just fine. Of course, by cheap I mean $100 esc and $100 motor. I bet an e-bike motor + esc would work fine too.

Like I was saying, you would need something to the tune of a 70kv motor if you use a 72 volt system and something to the tune of 200kv if you use a 24 volt system. You will need one heck of a beefy esc and wires to push 200 amps if you go with the lower voltage system.

ble2k   10 µW

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Re: I need some help!

Post by ble2k » Aug 26 2014 10:24am

parajared wrote:I imagine you could just toss a cheapie hobbyking esc + motor in the thing and be just fine. Of course, by cheap I mean $100 esc and $100 motor. I bet an e-bike motor + esc would work fine too.

Like I was saying, you would need something to the tune of a 70kv motor if you use a 72 volt system and something to the tune of 200kv if you use a 24 volt system. You will need one heck of a beefy esc and wires to push 200 amps if you go with the lower voltage system.
I have looked for many motors at hobbyking, but i'm not sure how it works exactly

Example:
http://www.hobbyking.com/hobbyking/stor ... Motor.html
this motor has 192kv, 80amps, 2750watt
192 * 24v = 4608 rpm thats fits
but how much power (watt) and amps has the motor at 24v?
are the amps fix and 24v * 80amps = 1920watt or can i control the amps in the esc

other example:
http://www.hobbyking.com/hobbyking/stor ... Motor.html
this motor has 172kv, 120amps, 5300watt
172 * 24v = 4128 rpm its ok
24v * 120amps = 2880watt??? or how i calculate it??

the esc i choose by the amps??
first motor something like that http://www.hobbyking.com/hobbyking/stor ... Ver4_.html or is that also ok http://www.hobbyking.com/hobbyking/stor ... _UBEC.html

can i control the speed with a servo tester (http://www.hobbyking.com/hobbyking/stor ... o%20tester) i have seen it in many videos at youtube

thanks you so much for your help

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