aquajet 775 prop selection

[bobswworld]

Hello,
I gave up on my dumas project, and went ahead and bought a used 775 that was already set up according to I THINK this sites recommended set up.
It has a graupner 700bb 8.4 motor, jetti 600, two 8 cell 3300 sc packs in parallel, and a 42 mm prop with a drive dog, in which I THINK is your upgrade prop for the cen 775, cause it has a sleeve, maybe i am wrong.
Was wondering if I went to a smaller diameter prop if I could get more run time, and draw less amps. Did some calculations, forgot where the formulas came from!! but it said I was using 49.5 amps, I only get maybe 3-4 minutes but it is very fast. Would I sacrifice the speed or would a smaller prop make it better? New to this field but am hooked once I drove this boat.
Oh also the batteries get pretty hot, the motor and controller are water cooled and seem normal temp as I can hold onto without a burn but not the batteries. Is it ok for this motor to run such high voltage?
Thanks in advance for any help

[Steven Vaccaro]

You could go down to a 40mm. But I think the problem are the cells. They shouldn't get that hot after 3-4 minutes. They have a high internal resistance.

[SJFE]

Those are the powerizer cells that cooked Roby76's big cat. I have had a failure with them also. I would suggest gp3300,elite4500 or the ib3600 cells.

[bobswworld]

Thanks for the speedy replies, the batteries make sense, as I said am new to this.
Forgot to mention that one pack was considerably hotter than the other. Guess I still got a good deal even having to buy new batteries. It runs wicked for 3-4 minutes.
Have priced new batteries and the powerizers seem to be half cost and I guess half reliable as well. will look into your suggestions sjfe
Is the voltage the norm for this fe setup, will this hurt this motor? according to the controller all seems ok with it. Just worried about the motor.
thanks

[SJFE]

Well it may live quite a while..or not. If you plan on running this boat for a while @ 14.2 volts I suggest the 700SC here @ OSE. That motor along with the new batteries will last you quite a long time.

[bobswworld]

Should it only run 14.2 volts, it is now running 16 cells, tested voltage at motor and it is seeing 22 volts at full charge!! I am concerned about this voltage. But it screams. maybe I confused parallel with series, but it is running 16 cells at 19.2volts

[kck741]

hey bobsworld do you have any other pics of your cen 775 I love that boat!!

[Steven Vaccaro]

Should it only run 14.2 volts, it is now running 16 cells, tested voltage at motor and it is seeing 22 volts at full charge!! I am concerned about this voltage. But it screams. maybe I confused parallel with series, but it is running 16 cells at 19.2volts

16 cells wears the motor out quickly. 14 cells is a good option.

As for one pack getting hotter. it could be there are not the same capacities. Packs will change with age.

For instance at full charge one may be 3300mah, but the other 2800mah. So where you are running after a while, one may run out before the other. This is a problem.

[skidooguymxz550]

change to deans. i don't know if they'll give you any more power but your connectors will never melt together whch is a pain.

mabey they will cool things down to. less rescistance

[bobswworld]

This was built this way when I bought it, it has one deans with the tamiya stuck in it, yeah I need to do that.
Where is the best place to get some quality batteries and still be able to make house payment?
Here are some pics
Was trying to use the FE calculator but it won't take any additional items, I input them but they dissapear. Was trying to add the jeti 600 controller.
Any Ideas?
This forum is great!!!

[mocars2]

Nice looking boat, very nice pics.

[kck741]

That boat is fine!!!

[ReddyWatts]

Go to the directory where fecalc is loaded, then open the text file and add the jeti there. Only add one line at a time just in case you enter something wrong, so you can go back and correct it. If you add something wrong the program will not open.

[bobswworld]

Hello again,
I took her out again this weekend with fully charged I guess junk batteries.
Went to run and it only ran good for about 30 seconds and just died off, so I stuck in two 1800 7.2 ncd venom packs I have for a Hammer and it run much better and actually longer. I am using a mrc 959 charger with settings set at whatever it picked for the 8 cells I believe they were at 3 amps with 30m/v peak hope I got that right.
Then I took them home and put them on charger and the 8 cell packs read over 10 volts each, but they would not run the boat like they did before.
Is there anything I can do with these packs to wake them up???
I am looking for more batteries but really not sure of what to buy.
Are tenergy any good, I know Intellects are supposed to be good but they really cost. I am not racing just having fun, but want something that will work good for awhile. Any suggestions? especially where to get them for a good price???
what was suggested by SJFE was gp3300, elite4500 or ib3600, have been looking but I guess not looking in the right places
thanks
Bob

[mocars2]

you said after charging the 8 packs they were 10 volts - that's normal - but didn't run like before. Didn't the boat only run for 30 sec. before - if so, then what happened then? Didn't these batteries come with the Ebay boat? Did you ask the old owner? you could charge them and dis-charge them a couple of times and see if that helps - hook them up to a auto tail light or just open your trunk and jump it to one of those tail lights, then charge them again but let them cool before you do that. Radio Shack had some GP 3300 for $24 for a 6cell last year, or maybe you can find some used on Ebay. They alway say 2 8 packs will heat up things and also shorten the motor life. 14 cells are better over all, not as hot and longer life on stuff.