Hi there guys and gals can anyone help me im tryin to convert a few things that are petrol driven, ive found several parts that i can use but dont no what runs best with what.I want to use 6x12v 33ah sealed lead acid batteries a 72 volt motor geared, but the gearing needs to get a speed of 18,000 rpm thats a problem, also i want use 3x12v alternaters to charge or to use as a power sorce at 36v and to prolong the life of the battery pack dont know if this can be done tho CAN ANYONE HELP…all info would be helpful to me and the rest of the world many thanks sparky.
The prop speed of most personal watercraft ranges from 6500-8500 RPM, the higher number would be found in some of the newer musclecraft models using ICE pushing 250HP. Spinning a prop at 18,000 RPM would be quite useless because even at 8500 RPM, the jet pump can move only so much water. Trying to stuff even more through it by turning it faster yields only minimal results because of the inefficiency of the jet pump. You could purchase an aftermarket performance pump but even then, you’re only gaining a few percentages on efficiency. You have to decide if it’s worth the $1200 expense for the pump.
Normally, a prop with a steeper pitch would be used to get more speed to make up for less prop RPM, resulting in less power and torque. However, there probably isn’t a prop steep enough to overcome the low RPM of most electric motors. You would have to gear it up, a ratio of 1:2 would bring the prop RPM up into the usual range, then you would need a motor with twice the torque and power that could actually get the prop spinning at that RPM under load… unless you got real trick with a multi-speed tranny.
Another option could be to overvolt a motor to get more RPM but this could cause the motor to burn up pretty quick.
It all depends how fast and how powerful you want this machine to be.
As far as sourcing parts? Probably going to need a machinist for the gearing and finding the right motor might take some trial and error. You’ll probably need larger/more batteries because 70% of the power generated is going to be completely lost through the inefficiency of the jet pump, just the nature of the beast.
thanks mpipes for your reply just wondering if you have ever owened a jet ski or to come to think of it any sort of motorbike i.e two stroke,these machines turn at very high revolutions in fact they turn twice as fast as a normal car whichturns at 7,000 rpm thats where people have gone wrong with electric motorbikes they need gearing before they get connected to the crank and thats the same with a jet ski they need gearing before they are connected direct to the crank thus thats why i need high rpm maybe not 18,000 but i need to give a little more for friction related problems i.e water lol so can you help then …many thanks sparky.uk
Yeah, I’ve owned numerous jetskis over the last 15 years and I’m involved in the jetski racing industry as well, what little there is of it.
Jetski engines do NOT turn high RPMs, they’re optimized to produce their power over a wider, lower RPM range because there are no gears, clutches or transmissions to rely upon. There’s no space, it’s extra weight, and given the wet/corrosive nature of the environment the manufacturers have opted to omit it. In fact, the prop itself is used as a gear of sorts for tuning performance. Steeper pitched props are used for higher speed but of course they reduce acceleration, and less aggressively pitched props produce more bottom end but speed drops. Where the prop driveshaft connects to the output shaft on the engine, that’s straight up engine RPM.
[QUOTE=mpipes;3513]there are no gears, clutches or transmissions to rely upon. There’s no space, it’s extra weight, [/QUOTE]
you sure about that tex? I know of a couple with gear reduction…they’re large couches.
but MOST do not, straight off the engine shaft…
I think a 5krpm motor would be great for a jet ski… just gotta waterproof it, put a waterjacket around (heat), seal the controller too. Bats should be fine as long as you keep the water drained (sump pump). You MAY want to just get a prop pitched for higher speed, it WOULD hurt accel with a normal ICE with a power curve like a bell, but a DC motor is more flat, and you get instant torque… its alot like gearing in a motorcycle.
I must say sorry to mpipes i was wrong had a look at my 650 sx manual and found that they do turn at low rpm,what a shocker…im trying to get an 1800 rpm motor and gear it at 1to5 ratio would that work i cant really afford to do trail and error so if anyone could show me any places to get a twin shaft motor a control switch and any other things that i would need it would be much apperciated im a bit clueless to it im more of a hands on man …many thanks for the advice about the prop pitch i will have to sort that out when ive got her in the water :).Im just wondering if anyone can shed some light on my theory of using 3x12v car alternaters,combined would they generate 36v or am i barking mad and could i use the power to drive the motor many thanks sparky uk
[QUOTE=frodus;3514]you sure about that tex? I know of a couple with gear reduction…they’re large couches.
but MOST do not, straight off the engine shaft…
[/QUOTE]
You’re right, there are a couple yamaha models (maybe Honda too, not sure) with gear reduction but they’re still not turning high RPM. They top out around 10,000 under load, higher when the pump loses traction. I tend to overlook those particular models because I’m more interested in racing applications and nobody races those particular PWC’s because they’ve proven to be not very good race platforms.
sparky, you could use alternators to charge the batteries while sitting on the beach but installing them inside the PWC and turning them with the electric motor will only result in a loss of power. It takes power turn alternators, the higher the load on them the more power it takes to turn them, so you won’t be able to harness any extra power from the electric motor to charge batteries nor extend the range.
for gearboxes…
http://surpluscenter.com/powerTrans.asp?UID=2008062611285678&catname=powerTrans
not sure if its what you need, but its a start…
here’s a motor too:
http://surpluscenter.com/item.asp?UID=2008062611285678&item=10-1899-A&catname=electric
sounds like this has been a tried and tested thing thats not much success, i was thinking about putting two impeller bodies together one behind the other makin one long tube with two blades inside i can fit them in my ski we have already measured it all out but would it make the performance any better or has this already been tested aswell or has no one tried it yet, im tryin find the best way to go with this project and not waste my time building things that wont work well. many thanks sparky
would these products be any good www.lemcoltd.com/lem_200.htm and www.lemcoltd.com/alltraxlmc.htm
[QUOTE=sparky71;3520]I must say sorry to mpipes i was wrong had a look at my 650 sx manual and found that they do turn at low rpm,what a shocker…im trying to get an 1800 rpm motor and gear it at 1to5 ratio would that work i cant really afford to do trail and error so if anyone could show me any places to get a twin shaft motor a control switch and any other things that i would need it would be much apperciated im a bit clueless to it im more of a hands on man …many thanks for the advice about the prop pitch i will have to sort that out when i’ve got her in the water :).Im just wondering if anyone can shed some light on my theory of using 3x12v car alternaters,combined would they generate 36v or am i barking mad and could i use the power to drive the motor many thanks sparky uk[/QUOTE]
DONT go with the alternators. 1: they have negative ground. so if you hook them up in series to add voltage you will short two of them out. 2: I have seen sailboats try to recover power, but with losses they have had little luck.(except with a towed or wind generator). A Jetski will get NO, (none, nada, zilch), power back. You couldn’t force enough water through that hydrojet at a hundred miles an hour to get any usable power back.
Your basic premise to use a small high RPM motor to drive it should work. Try to get the curve for the ICE engine you are replacing. Then get an electric that comes close at least on a couple of points. When you convert from gas to electric you will get different performance. Rather than debate who’s jetski does what, get the manufacturers RPM VS torque curve for your jetski. If your electric is very different, ( it probably will be), you may need to adjust pitch, or gear ratio. If you do not want to do this give it your best shot, (I.E find a motor with the closest RPM range you can), (I think RPM is more important than HP as you can overdrive a well cooled electric by 2.5 to 1 or better) the worst that will happen is you will pay for inefficiency in performance or electricity. I am currently converting a car and a big boat, let us know how it works, just seal everything, (electricity and water dont mix). and good luck.
[QUOTE=sparky71;3520]I must say sorry to mpipes i was wrong had a look at my 650 sx manual and found that they do turn at low rpm,what a shocker…im trying to get an 1800 rpm motor and gear it at 1to5 ratio would that work i cant really afford to do trail and error so if anyone could show me any places to get a twin shaft motor a control switch and any other things that i would need it would be much apperciated im a bit clueless to it im more of a hands on man …many thanks for the advice about the prop pitch i will have to sort that out when i’ve got her in the water :).Im just wondering if anyone can shed some light on my theory of using 3x12v car alternaters,combined would they generate 36v or am i barking mad and could i use the power to drive the motor many thanks sparky uk[/QUOTE]
DONT go with the alternators. 1: they have negative ground. so if you hook them up in series to add voltage you will short two of them out. 2: I have seen sailboats try to recover power, but with losses they have had little luck.(except with a towed or wind generator). A Jetski will get NO, (none, nada, zilch), power back. You couldn’t force enough water through that hydrojet at a hundred miles an hour to get any usable power back.
Your basic premise to use a small high RPM motor to drive it should work. Try to get the curve for the ICE engine you are replacing. Then get an electric that comes close at least on a couple of points. When you convert from gas to electric you will get different performance. Rather than debate who’s jetski does what, get the manufacturers RPM VS torque curve for your jetski. If your electric is very different, ( it probably will be), you may need to adjust pitch, or gear ratio. If you do not want to do this give it your best shot, (I.E find a motor with the closest RPM range you can), (I think RPM is more important than HP as you can overdrive a well cooled electric by 2.5 to 1 or better) the worst that will happen is you will pay for inefficiency in performance or electricity. I am currently converting a car and a big boat, let us know how it works, just seal everything, (electricity and water dont mix). and good luck.
many thanks Bill for your help it is most welcome i have already scraped the idea of 3 alts and using geared ratio as this loses about 30% of your drive and have opted for chain and sprocket which only loses about 5% that at the most,I am going to use a perm132 motor kit at 48volts dont no what car batteries to use yet 55ah or 44ah not sure on that bit yet this run at nearly 3000 rpm at a constant 125ah but would two impeller bodys work better than one forcing twice as much water though giving me better efficiency and thrust. many thanks sparky 71
No, “stacking” two impellers on one shaft will decrease your efficiency. Between the pump intake stuffing the impeller with water at full speed and the impeller pressurizing the water into the outlet nozzle, one impeller is as good as it gets.
You could modify the hull to fit two jet pumps side by side but you won’t really have any gains. It could increase the acceleration but it puts more load on the motor, so now you have to upgrade everything up along the driveline to achieve any extra performance.
i got ya m pipes ill stick with a single body for the time being im going start the build in two weeks so wish me luck 
hey guys just found a few websites with 48 volt alts could i use one of these to keep the batteries toped up http://www.casproducts.ca/ http://www.electrodyne.com/about.html http://www.americanpowerinc.com/highoutputalternators.htm and http://www.asianproducts.com/showproducts.php?item_id=P11498197800163244&pic=big would i need to use a control unit to regulate the charge many thanks sparky uk
total strip down
You’re not going to recoup ANY battery power using an alternator in an electric jetski.
It’s NOT going to happen.
It will, in fact, require MORE motor power to turn the alternator in addition to moving the jetski. The alternator will never output more power than what goes into turning it, and the end result is you just drain the batteries even faster trying to get more range out of the system.
hi guys just an update ive ordered my motor kit from usa so im waiting on that, so for the time being ive stripped my ski down and resprayed it, but im stuck with what sort of batteries to go for i was going for sealed acid at 65ahx4 giving me 260 ah and 48v but now im not so sure. My kit can run upto 300amps,so with that in mind im thinking of using aa batteries ni-cad ive found box units you can fit 10 aa’s into but to get to close to the 300 mark i would have to run 130 aa’s @1.2v 2700mamps giving me 285 ah but then that shoots the voltage up to 158 volts, would that cause a problem for the control unit or the motor, my motor can only handle 48v also how the hell would i charge it. Any help please that means you mpipes lol my kit link is http://www.electricvehiclesusa.com/product_p/ki-etekdelux.htm
Ah does not add up when you put batteries in series. 48V 65Ah… Voltage adds in series but not parallel. Current adds in parallel but not series.
You should start thinking in Watt Hours (Wh). 48V 65Ah is 3120Wh.
My kit can run upto 300amps,so with that in mind im thinking of using aa batteries ni-cad ive found box units you can fit 10 aa’s into but to get to close to the 300 mark i would have to run 130 aa’s @1.2v 2700mamps giving me 285 ah but then that shoots the voltage up to 158 volts, would that cause a problem for the control unit or the motor, my motor can only handle 48v also how the hell would i charge it. Any help please that means you mpipes lol my kit link is http://www.electricvehiclesusa.com/p…-etekdelux.htm
don’t use nicads, they lose life pretty quick. Don’t use aa’s either, you’ll have to weld them. Each connection you make loses power, so your losses are going to be HIGH. Each connection will have a resistance, and at 300A it doesn’t take much resistance to heat up. Again, you’re calculating Ah wrong. 130AA’s would be 156V 2.7Ah. You wouldn’t even turn that motor. Comparing SLA’s to AA’s, aa’s would give you 421.2Wh. Not even CLOSE to what you’d need. You’d need almost 1000 of them just to get the Ah comparible to lead acid, but then you’d need even more because of connection losses. SLA’s would take up tons less room. Use what others are using for their system, since this is an a-typical vehicle. Use 48V 65Ah leads, you’ll like them. You can always get larger batteries as well, you ARE removing the engine/exhaust/original battery/intake/waterbox.
One more thing to think of, you’re batteries will NEVER see 300A. When you’re in low throttle, you’re power to the motor is the same as the power going in. Lets say at 25% PWM when starting from dead stop, the average voltage is 12V, but the current is 300A, giving 3600W. The battery pack is sitting at 48V, but it might only see 75-80A for a total of 3600W. It will never see more than 100A on the battery side. Power in is a little more than power out (some losses in the controller). My motorcycle outputs somewhere around 350A to the motor, but the batteries only see 75A of that. You don’t need 300A batteries, you will only need to run MAYBE 100A, and thats from dead stop. Once RPM’s rise, your current drops substancially, but power stays the same. Think of the controller as a power converter. The output is limited to 300A, the input is typically going to be MUCH MUCh lower than that.
Charging is another thing altogether. I’d recomend getting 4 12V chargers and making some plugs to charge when you get home. Then each battery would be balanced.