Search found 4298 matches

by coulomb
Fri, 17 Jul 2009, 15:00
Forum: Batteries, charging, management and monitoring
Topic: Li cell discharge tests
Replies: 67
Views: 9788

Li cell discharge tests

Oh, right! I thought you just used 120A as the current. Well done.
by coulomb
Fri, 17 Jul 2009, 14:14
Forum: Batteries, charging, management and monitoring
Topic: Li cell discharge tests
Replies: 67
Views: 9788

Li cell discharge tests

Did you calculate the internal resistance by taking the V drop from the 3.57 figure? Yes, I did. That high initial voltage seems to be due to some sort of "surface charge" effect similar to a PbA battery and the rapid voltage drop occurs because of this charge dissipating rather than being lost acr...
by coulomb
Fri, 17 Jul 2009, 05:05
Forum: Batteries, charging, management and monitoring
Topic: Thundersky Impedance values
Replies: 15
Views: 3979

Thundersky Impedance values

Using the Weber and Coulomb Standard Method for voltage sag (internal resistance normalised for battery capacity), we did some measurements on some Sky Energy SE40AHA cells today. Our method is as follows: First wait for the voltage to settle down (after charging) or settle up (after discharge). I l...
by coulomb
Fri, 17 Jul 2009, 04:09
Forum: Batteries, charging, management and monitoring
Topic: Prius Batteries in Australia
Replies: 26
Views: 5790

Prius Batteries in Australia

I guess that's why they call the epicyclic gear in the Prius a "torque split device", not a "torque amplifying device" or similar. I have seen a conversion that attempts to use the Prius motors complete with epicyclic gear by welding some of the gears (panetary from memory) to their carrier. He call...
by coulomb
Fri, 17 Jul 2009, 03:58
Forum: Batteries, charging, management and monitoring
Topic: Prius Batteries in Australia
Replies: 26
Views: 5790

Prius Batteries in Australia

Maybe more of a Prius style system using two motors to get a much wider useful rpm range without actual ratio changes would work well... The way the Prius does it, you'd need three motors. The Prius does "low gear" by running the motor at high speed and low torque, and uses much of the excess speed...
by coulomb
Fri, 17 Jul 2009, 02:18
Forum: Batteries, charging, management and monitoring
Topic: Sky Energy LiFePO4 Bulk Buy this Week
Replies: 48
Views: 11771

Sky Energy LiFePO4 Bulk Buy this Week

These are the straps that come with the Sky Energy cells: http://forums.aeva.asn.au/uploads/689/straps1.jpg       http://forums.aeva.asn.au/uploads/689/straps2.jpg Note how the straps are laminated (for lower eddie currents http://forums.aeva.asn.au/smileys/smiley2.gif ), are kinked (so the cells ca...
by coulomb
Fri, 17 Jul 2009, 02:08
Forum: Members Machines
Topic: Weber and Coulomb's MX-5
Replies: 1698
Views: 400502

Weber and Coulomb's MX-5

For more photos of these cells, see this Sky Energy LiFePO4 Bulk Buy this Week thread.

Edit: For voltage sag measurements, see this Thunder Sky impedance post.
by coulomb
Thu, 16 Jul 2009, 22:11
Forum: Batteries, charging, management and monitoring
Topic: Li cell discharge tests
Replies: 67
Views: 9788

Li cell discharge tests

As a point of interest, that works out to about 4.3 mR internal resistance, or 173 mV/C for capacity independence (just multiply internal resistance by the capacity in Ah). BTW, the C here isn't degrees centigrade, it's the number 40 for a 40 Ah cell. This agrees rather well with a measurement of 17...
by coulomb
Thu, 16 Jul 2009, 22:08
Forum: Batteries, charging, management and monitoring
Topic: Li cell discharge tests
Replies: 67
Views: 9788

Li cell discharge tests

Had to keep adding water to try and keep the current fairly constant - it got pretty warm. I think you might need some more water; we use about 1.5 litres. I guess we could use a bit more. We find that stirring the water also keeps the current up a bit. I guess the ultimate would be a 4L ice cream ...
by coulomb
Thu, 16 Jul 2009, 22:03
Forum: Batteries, charging, management and monitoring
Topic: Li cell discharge tests
Replies: 67
Views: 9788

Li cell discharge tests

With respect to the "Permission denied" problem: check this post of mine from a week or two ago:

viewtopic.php?t=1298
by coulomb
Thu, 16 Jul 2009, 20:32
Forum: Batteries, charging, management and monitoring
Topic: Sky Energy LiFePO4 Bulk Buy this Week
Replies: 48
Views: 11771

Sky Energy LiFePO4 Bulk Buy this Week

And here are some of them: http://forums.aeva.asn.au/uploads/689/sky_energy_boxes_1.jpg     http://forums.aeva.asn.au/uploads/689/sky_energy_boxes_2.jpg Each box came with a hand filled in form with various numbers and the cell's internal resistance (as they measure it). The largest box actually had...
by coulomb
Thu, 16 Jul 2009, 14:24
Forum: Batteries, charging, management and monitoring
Topic: Sky Energy LiFePO4 Bulk Buy this Week
Replies: 48
Views: 11771

Sky Energy LiFePO4 Bulk Buy this Week

Our 212 SE 40 Ah cells are due to be delivered this morning.
by coulomb
Thu, 16 Jul 2009, 14:08
Forum: Batteries, charging, management and monitoring
Topic: Prius Batteries in Australia
Replies: 26
Views: 5790

Prius Batteries in Australia

They're 6.5 Ah cells, and work out to 201.6 V nominal (168 * 1.2). Being NiMH, he energy per weight is worse than lithium iron phosphate, but not dramatically so. (Edit: That works out to 1.31 kWh nominal, of which less than half is used in a stock Prius (~40% to 80% SOC).) (Edit2: That's Gen II; I ...
by coulomb
Thu, 16 Jul 2009, 00:28
Forum: General EV Discussion
Topic: Brisbane or near
Replies: 1
Views: 691

Brisbane or near

PIM sent
by coulomb
Wed, 15 Jul 2009, 14:56
Forum: Batteries, charging, management and monitoring
Topic: Sky Energy LiFePO4 Bulk Buy this Week
Replies: 48
Views: 11771

Sky Energy LiFePO4 Bulk Buy this Week

An update from Powered by DC:

http://www.nabble.com/forum/ViewPost.jt ... 1&framed=y

Sounds like there is another Sky Energy bulk purchase about to close.
by coulomb
Wed, 15 Jul 2009, 03:13
Forum: Batteries, charging, management and monitoring
Topic: Care and feeding of baby Thunder Skys
Replies: 4
Views: 1095

Care and feeding of baby Thunder Skys

I just love how Lithium information has to be gleaned from vague hints and fokelore. Below is an example from EVDL at http://www.evdl.org/archive/index.html#nabble-to22981597|a23002882 . Question is: do we believe this? Do we need to do the same thing to Sky Energy cells? Other Lithium cells? ======...
by coulomb
Tue, 14 Jul 2009, 21:26
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

coulomb, just to clarify. A non overvoltaged 22kW motor can't even imagine 100kW. up around 66kW on a good day would be the limit. Yes, of course. Sorry, was thinking of the MX-5, which has a 1.7x overvoltage. So my point is, even though with overvoltaging you can get a pretty spectacular ratio of ...
by coulomb
Tue, 14 Jul 2009, 18:50
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

Perhaps peak power needs to be something like 10 times average in a vehicle. So peak power needs to be 10 times the cruise at 100kmph power. That leaves 7.5kW motor out ? 10 to 15 kW seems more likely. In an extreme sports high power vehicle perhaps; say 15 kW @ 100 km/h and 150 kW @ peak accelerat...
by coulomb
Tue, 14 Jul 2009, 16:19
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

I'm not sure why weber wants so much info on temperature rise. Surely the point of these experiments was to ascertain whether the rewound motor really produced the power that we hoped it would - and it appears it has. Yes, that's the main result, and it certainly appears that it has. The only point...
by coulomb
Mon, 13 Jul 2009, 16:49
Forum: Members Machines
Topic: Camira Conversion
Replies: 33
Views: 7475

Camira Conversion

Just rectifying 240 VAC would give pulsating DC from 0 to about 340 V, which is not suitable for direct connection to the pack. It may be possible to replace a 3-phase alternator with one that produced lower voltage, and 3-phase AC rectified (6 diodes) is not so bad for charging with. You would alte...
by coulomb
Mon, 13 Jul 2009, 07:03
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

G forces? Is this something to do with sensitive inductor cores or something? Other than that, what could be sensitive about industrial drive electronics that doesn't apply to "vehicle grade" drives?

No, at least this guy doesn't realise that.
by coulomb
Mon, 13 Jul 2009, 06:25
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

Firstly, that paper. Give me a break ! What it really said was that for any reasonable quality motor that the efficiency may change by up to about 1% motor to gen at working torque, assuming the accuracy of the instrumentation used could resolve that ! But 82% isn't reasonable. For low efficiency m...
by coulomb
Mon, 13 Jul 2009, 01:28
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

But how much more efficient can an induction generator be, compared to its motor efficiency? Same efficiency, no brainer DOL. With VF is up to the VFD how well it handles it though. Um, not according to this paper: http://www.esat.kuleuven.be/electa/publications/fulltexts/pub_1602.pdf From the conc...
by coulomb
Mon, 13 Jul 2009, 00:17
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

The two motors may have varied inversely in efficiency ? I have no way of telling. Exactly! There are an infinite number of pairs of efficiency-vs.-power curves for these two motors that would give the measured results. Well, yes, in the same sense that there are an infinite number of real numbers ...
by coulomb
Mon, 13 Jul 2009, 00:02
Forum: Electric motors and controllers
Topic: Changing an induction motor voltage
Replies: 436
Views: 125492

Changing an induction motor voltage

I think we should give both motors half a percent inefficiency each, so that's 6.23 * .715 * .815 = 3.63 kW, very close to what was measured. Actually, thinking about this, it seems to me that the load motor is also a bit beyond its comfort zone. Its nominal speed is ~3000 rpm, so it's already over...