Search found 54 matches

by vk4bxi
Dec 08 2018 9:55am
Forum: Battery Technology
Topic: Large lead acid forklift battery self discharging
Replies: 20
Views: 1107

Re: Large lead acid forklift battery self discharging

As regards the existing Battery. A shorted cell or two is probable. Shorts across the cell is not so likely since there is usually something like a fibreglass mat to keep the two parts of the cell apart. Plate material usually crumbles off of the plate due to miss use and gathers in the bottom of th...
by vk4bxi
Dec 07 2018 10:32am
Forum: Battery Technology
Topic: Battery Distances and Layout
Replies: 4
Views: 337

Re: Battery Distances and Layout

Your school connection reference is correct ! in this way both sets of batteries will always share properly. If you do your charging that way as well, all should be fine. Proving that connection method is correct is easier to try rather than do the maths ! The method should work for two up to many b...
by vk4bxi
Aug 21 2017 10:34am
Forum: General Discussion
Topic: 100W resistor, how much is too hot?
Replies: 7
Views: 637

Re: 100W resistor, how much is too hot?

well it depends largely on the heat sinks that you using and how well they are thermally connected. That kind of temperature rise is fast. Are the heat sinks coming up to a similar temperature ? Also I assume that you want to load test the battery pack and a one minute load on time is not what you w...
by vk4bxi
Jul 13 2017 1:37am
Forum: General Discussion
Topic: Tesla gearless cars?
Replies: 30
Views: 2608

Re: Tesla gearless cars?

Ah well ! that last comment surprised me. Field weaken permanent magnet motors ? To be sure I contacted someone who is a real authority on this stuff. Sure enough you can do a few tricks when you have significant stator current flowing, but that's likely to come and bite you when the current is remo...
by vk4bxi
Jul 05 2017 10:49pm
Forum: General Discussion
Topic: Tesla gearless cars?
Replies: 30
Views: 2608

Re: Tesla gearless cars?

Motors with permanent magnet rotors or fields can only change speed with a change in applied stator or armature voltage. An induction machine can (with a good controller) play with the flux in the stator and achieve a approximately 3:1 range of field weakening. I.E. the motor can spin at ~ 3 faster ...
by vk4bxi
Apr 25 2017 12:35am
Forum: Battery Technology
Topic: Inrush current limiting maths
Replies: 2
Views: 336

Re: Inrush current limiting maths

Hi, at these sort of current and power levels one normally doesn't mess around with thermistors etc. A substantial resistor (think 50watt metal clad but no heat sink) and then a heavy duty power relay or contractor to bridge the resistor out after a second or two. You are not worried about weight or...
by vk4bxi
Mar 12 2017 5:55pm
Forum: Alternative Energy
Topic: Off grid standalone electricity supply project
Replies: 10
Views: 1380

Re: Off grid standalone electricity supply project

What are you measuring the output volts with ? I would guess that the ups has a modified square wave output. So the peak volts will be d├ępendant on the battery volts and the time the volts are on will give the rms. And an ordinary DVM will be reading average and not a true reflection of what is goin...
by vk4bxi
Mar 08 2017 5:14pm
Forum: Motor Technology
Topic: Reducing motor weights... with Al wire?
Replies: 11
Views: 1449

Re: Reducing motor weights... with Al wire?

Hi guys, This is a theme that has been repeated many times over the years with motors, transformers, overhead power cables etc. Yes the combination of weight and conductivity of aluminium is better than copper.......but ! Aluminium is a bitch to make and keep good joints especially when exposed to t...
by vk4bxi
Mar 07 2017 7:07pm
Forum: E-Bike General Discussion
Topic: Bicycle Locks
Replies: 114
Views: 10727

Re: Bicycle Locks

What happened to the idea of using hollow tubing filled with nasty stuff under pressure ...mace etc. Cut that open and you won't be in a hurry to go further ? I saw an add for something like it, or was it an April fools day joke ?
by vk4bxi
Jan 26 2017 4:22am
Forum: E-Bike Technical
Topic: Specific heat absorption capacity of disc brakes
Replies: 147
Views: 10939

Re: Specific heat absorption capacity of disc brakes

The other thing that needs to be considered is that the heat is generated in the surface skin of the brake rotor. There is very little time for that heat to progress into the body of the rotor during a few seconds of " oh my god braking", serious brake fade ( or when the brakes lose it ) kicks in ab...
by vk4bxi
Jan 24 2017 5:10pm
Forum: E-Bike Non-hub Motor Drives
Topic: BBS01 with 28T cluster? and 42T chain ring?
Replies: 5
Views: 549

Re: BBS01 with 28T cluster? and 42T chain ring?

Yes same here ! Brisbane also has got hills !! my wife rides with me but without a motor, but she has to get off and walk the worst ones.
As you said the bike is for exercise, and for fun, but hills are not fun.

Bob
by vk4bxi
Jan 23 2017 10:19pm
Forum: E-Bike Non-hub Motor Drives
Topic: BBS01 with 28T cluster? and 42T chain ring?
Replies: 5
Views: 549

Re: BBS01 with 28T cluster? and 42T chain ring?

with (only) a BBS-01, a 34 tooth gear on the back is the least I would go to. I run a 42:34 with a BBS-02 750 watt and have to peddle some on the steepest grades. When I did my conversion I did some calculations and actually measured the grade of my steepest local hill ! (inclinometer). And decided ...
by vk4bxi
Jan 12 2017 7:26pm
Forum: E-Bike Build Threads / Photos & Video
Topic: New lighting setup for BBSHD Fat
Replies: 45
Views: 5066

Re: New lighting setup for BBSHD Fat

Has anyone measured the current draw please.

Bob
by vk4bxi
Jan 10 2017 5:04pm
Forum: Battery Technology
Topic: Looking for a reliable 14S 40A bms
Replies: 16
Views: 795

Re: Looking for a reliable 14S 40A bms

Hi I'm running the pf cells as well in a 13S4P configuration with a 20 Amp current limit on my BBS 02 750. 5amps per cell for 30 seconds is definitely as much as I would want to pull from the pack. When the pack is fully charged things are OK and "sag" is good. But the "sag" seems to increase badly ...
by vk4bxi
Jan 02 2017 5:58pm
Forum: E-Bike Non-hub Motor Drives
Topic: Bafang BBSxx - fault finding and fixes
Replies: 1040
Views: 161387

Re: Bafang BBSxx - fault finding and fixes

Hi guys, While we are talking grease jobs. My bbs 02 750watt is coming up for ~1000km. I greased the final gears at about 500km.......they were just starting to get noisy (very little grease left there) .Now of course I worry about the primary pair of gears. Searches show what to do, but not very mu...
by vk4bxi
Dec 01 2016 5:16am
Forum: E-Bike General Discussion
Topic: How To, 50A BBSHD Controller Mod
Replies: 237
Views: 33515

Re: How To, 50A BBSHD Controller Mod

Ah hah, Things start to make more sense to me now. When designing cyclo convertors one is always limited by the volts available because the supply transformers are one of the more expensive parts of the design and more volts cost money. Here we are limited by the battery volts as to what speed we ca...
by vk4bxi
Nov 30 2016 10:52pm
Forum: E-Bike General Discussion
Topic: How To, 50A BBSHD Controller Mod
Replies: 237
Views: 33515

Re: How To, 50A BBSHD Controller Mod

Ok......I sort of get that but, I have designed and commissioned a few of these drives at multi megawatt levels. The thing should be symmetrical, I suspect that it will be the built in body diode losses and capacitance to the casing that might be the culprit. even so a 9 off solution sounds like an ...
by vk4bxi
Nov 30 2016 5:27pm
Forum: E-Bike General Discussion
Topic: How To, 50A BBSHD Controller Mod
Replies: 237
Views: 33515

Re: How To, 50A BBSHD Controller Mod

I'm sure that it has been nailed down somewhere else....please let me have the link......but as far as I know, three phase motor controllers normally use their output devices in groups of 6 so if you want to "beef-up" an output stage you double up and use two devices per output element and thus you ...
by vk4bxi
Nov 09 2016 5:43pm
Forum: Battery Technology
Topic: Best Charger for me please
Replies: 4
Views: 449

Best Charger for me please

Hi I've just scored a bunch of "dud" 18 volt 5Ah Milwaukee power packs. The next thing for me is check the cells out prior to making up new packs of useful sizes . I have all of the usual power supplies with current limit etc. But what I need is a charge/discharge unit that will shut off at the corr...
by vk4bxi
Nov 02 2016 6:49pm
Forum: Items Wanted
Topic: any bargains going at Canadian tyre
Replies: 1
Views: 328

any bargains going at Canadian tyre

Hi I live in Oz and am going to Canada on a quick 3 day trip. I want to get hold of 1S ~ 14 Ah of li-ion cells to increase my 13S 4P PF setup to 14S. I wonder if there are any cordless tool battery pack "bargains" going that could suit my needs that the group could recomend. (that way I can safely p...
by vk4bxi
Oct 25 2016 9:46pm
Forum: Battery Technology
Topic: Common pack design mistakes, how to avoid?
Replies: 257
Views: 39597

Re: Common pack design mistakes, how to avoid?

IMG_3369_1.jpg Many years ago in a undergrad tutorial we worked out the "correct" way to parallel things like battery's and stuff. and attached was the correct way. If you have a lot of things (resistors or battery's) in parallel then feed in from one side and out from the other. That way all of th...
by vk4bxi
Oct 11 2016 7:34pm
Forum: E-Bike Technical
Topic: Ebike Circuit Protection, Fuses and Circuit Breakers
Replies: 44
Views: 6868

Re: Ebike Circuit Protection, Fuses and Circuit Breakers

Oh yes !, for spec junkies like me these look very good. but its the difference between $20 and $4 for the Chinese stuff. As always you get what you pay for if you are lucky!

Regards Bob
by vk4bxi
Oct 10 2016 5:24pm
Forum: E-Bike Technical
Topic: Battery Cable Size, Power Loss
Replies: 9
Views: 779

Re: Battery Cable Size, Power Loss

Nice work in progress. But remember as you reduce circuit resistance you also increase fault current. You may have to relook at fusing/ circuit breaker ratings. Most breakers run out of "steam" above 5kA

Bob
by vk4bxi
Oct 06 2016 5:19pm
Forum: E-Bike Technical
Topic: Ebike Circuit Protection, Fuses and Circuit Breakers
Replies: 44
Views: 6868

Re: Ebike Circuit Protection, Fuses and Circuit Breakers

If the spec's are true then it looks very good. Permanent magnet blow out style breakers are the "right" stuff for DC battery systems. The only Caveat is........don't get the polarities wrong ! if you do it will likely melt after a couple of bangs. I tend to suggest ones without permanent magnet mag...
by vk4bxi
Sep 28 2016 10:44pm
Forum: E-Bike Technical
Topic: Ebike Circuit Protection, Fuses and Circuit Breakers
Replies: 44
Views: 6868

Re: Ebike Circuit Protection, Fuses and Circuit Breakers

Yes the blue sea seems a nice breaker and should work fine. A choice from an old employer would be from Schneider, they do 60 volts per pole. But note that you can get ganged poles from them so two poles wired in series = 120 volt DC rating. (and of course 3 would get you 180 volts !!) Note these ar...