Well, I don't NEED a 12kw motor but I HAVE one and I will be testing it. It doesn't cost any significant extra amount of energy to run the bigger motor at a given power level and I suspect the bigger motor will dissapate heat better.
If you think my power consumption at 4kts is excessive, that is the sort of observation that is useful to me. I will look into that. Maybe my battery voltage is sagging at that power level, I don't know. It shouldn't, as it is a 220ah bank giving a discharge/capacity ratio of .27, which is significant with flooded lead acid batts, but not excessively so I don't think. I did have a voltage meter installed originally but it was a cheap digital one and it bit the dust, as did its replacement. I have a nice Simpson panel voltmeter I will be installing at some point, like maybe when I decide exactly where the final instrument panel will be. I have not been watching the B voltage with my multimeter during testing because I dont have enough hands and eyes to operate the vessel safely and do a whole lot of other stuff at the same time.
The volt/RPM constant of the 5kw motor that was just tested is 50, so it is a somewhat slower turning motor than say a ME0907. I am running a 2:1 reduction gear which shouldnt be too far out of the envelope. Full power gave me 950 prop RPM. So 1900 motor RPM. Ideally my full power motor RPM, going by the constant, would be 2400RPM. So increasing the reduction ratio would maybe make SOME difference, but not a lot. However these Baldor gearboxes only come in whole number gear ratios so it has to be either 2:1 or 3:1. Intuitively I don't think the gear ratio is a problem. Motor never overheats or anything like that. Output RPM should be acceptable for this prop.
I may do another round of testing with the 5kw motor first, after temporarily installing the voltmeter. I think I need to make sure the voltage is not sagging excessively under load.
Flash Update
I just realized I haven't really checked the batts in a while. Battery water was a little bit low, but plates still well covered. I did have some iffy connections, though. Cable terminals were the setscrew compression type which in retrospect was maybe a bad idea. Filled the cells almost to the bottom of the fill tubes, cleaned the battery tops and the cable terminals, tightened everything up. I may have had some significant losses there. So definitely there will be another round of testing with this motor before switching to the ME0913. Sagging voltage could have increased the current needed for a given speed, and this would be more pronounced at higher (relatively speaking) speeds I guess.
It was encouraging to see that while the water was low, it was about the same in the entire bank, and SG in the cells I tested was pretty close. I did not check each individual cell, which would be pointless until a charge cycle or two after filling. I will do a couple of charge cycles and then record the SG. But from the consistent water levels I would say all cells are fully functional after 3 years, so my $85 Sams Club batteries are holding up okayish for the money. I just want to get 2 or 3 more good years out of them and I will be satisfied, and anything extra is just extra.
FWIW, a 6hp gasoline outboard at half throttle pushes the boat at about 4 kts or a hair less. So I am thinking a bit more than 1 shaft horsepower would be needed, though not much more, to get that speed. I still have the original sailing keel so its not just a slick hull.
---In electricboats@yahoogroups.com, <no_reply@yahoogroups.com> wrote :
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a New Topic | • | Messages in this topic (8) |
No comments:
Post a Comment