Possibility of putting 66V through an MXUS DD rear hub?

[dnmun]

it looks like the one labeled 13.8V is on the 12V rail. the other charge pump caps have the 13.4V.

so you used 330R for the power resistor. @50mA that is 16.5V so 61.5-16.5=45V to the regulator.

 

[monkeychops]

Jeremy noted earlier in the thread:

"The voltage regulator is an LM317K, which has an absolute maximum differential input voltage of 40V, so the max at its input would be around 52V"

So 45V should be ok.

 

[Jeremy Harris]

Looks OK to me. You only need a thin smear of the thermal compound, it's a case of less is better usually. The 330 ohm resistor looks right to me (orange-orange-brown) but will probably have a tolerance of 5% , so could measure anything between 314 and 346 ohms, so your measurement seems OK, too.

 

[dnmun]

yes, i think the general assumption is that the regulator can drop up to 40V but the most i have ever done was with 54V input to the regulator and 19V on the 12V rail so that was 35V drop across the regulator. but it also had a 510R resistor in parallel too.

i think you coulda squeezed by with the original setup but the 180R was really small. usually it is 330R on the 36V controllers anyway. you coulda gone all the way up to the 580R like he said too.

the high values like 600R+ are only a problem when the battery voltage is really low and the power resistor drops the voltage input to the regulator so much that the regulated voltage on the output of the regulator is so low it won't turn on the transistors.

but 180R will work even down to 24V too and i think that is why they used it.

 

[monkeychops]

Thanks again chaps. Will report back later.

 

[monkeychops]

Update:

The 3S batteries arrived 3 weeks after ordering them. Turnigy 30S 4000mAh ones. They seem fine.

First thing I noticed after connecting them all up with my various wiring harnesses was that the total pack voltage measured 36V. What the flip, I was expecting 60V! It turns out I had tried to serial together 48V and 12V with polarity reversed. I had the tips of my new parallel harness (for the 3S cells) round the wrong way. Pointy tip (on the 4mm bullets) should have been -ve and hollow tip +ve, as they are on the end of the bricks themselves. Can't help wondering why there wasn't a 'bang' when I connected them up wrong.

2nd thing I noticed was the top speed improvement. My best guess is that's its around 4 or 5 mph more (measured using GPS). Which is perfect for me. Top speed on the flat now 28-29mph. Possibly this would reach 30mph in warmer weather.

3rd thing I noticed was total loss of power 6 miles into my 15 mile commute. Fuse problems. Took out the fuse, noticed it was blackened but intact. Re-inserted and power returned. Cycled gingerly the rest of the way. Got to work, took the fuse out again, re-inserted and no power again. Confession time: it's a 20A fuse and the controller pulls 22A. It had been fine up till now (on 48V). Anyway, I fashioned a temporary one made from a paperclip to get me home:



Which worked. Fuse now replaced with a 30A one.

Also bought this for bulk charging: http://www.ebay.co.uk/itm/380507774625?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Seems fine so far. Voltage and current adjustable.

So all good. Thanks again chaps, will report back if there are any interesting developments. Hopefully not though!

 

[Jeremy Harris]

The fuse problem may well be the fuse holder not making good contact with the end of the fuse, so allowing it to heat up and corrode, resulting in the loss of power. Removing and replacing the fuse clean it enbough to get it going again, but I suspect the problem will recur unless the fuse holder is either replaced or a way found to get a better contact with the end of the fuse.

Glad the rest of it's all working OK. Power and speed is addictive, though, and an extra 5mph will git your range pretty hard, too, if you use it. Power used is proportional to the cube of speed, more or less, so increasing speed by even a few mph makes a big difference to power. For example, doing 30mph needs a bit less than double the power needed to do 25 mph (i.e. if you needed around 500W for 25mph you'll be something like 900W or so for 30mph). This means that range at 30mph will be getting on for half that at 25mph.

 

[monkeychops]

The fuse problem may well be the fuse holder not making good contact with the end of the fuse, so allowing it to heat up and corrode, resulting in the loss of power. Removing and replacing the fuse clean it enbough to get it going again, but I suspect the problem will recur unless the fuse holder is either replaced or a way found to get a better contact with the end of the fuse.

Good point about the fuse holder. I will give it a bit of an inspection. Plus the bit where it screws into on the bike needs checking.

Glad the rest of it's all working OK. Power and speed is addictive, though, and an extra 5mph will git your range pretty hard, too, if you use it. Power used is proportional to the cube of speed, more or less, so increasing speed by even a few mph makes a big difference to power. For example, doing 30mph needs a bit less than double the power needed to do 25 mph (i.e. if you needed around 500W for 25mph you'll be something like 900W or so for 30mph). This means that range at 30mph will be getting on for half that at 25mph.

I understand what you are saying. In my situation I am being limited by the 22A current limit on the controller. Maximum power on 49V was approx 1078W. Now it is 1342W (obviously depending on battery charge level). But since that extra power has been provided by more batteries of the same capacity in series with the existing ones, the whole pack is still 16Ah total capacity. So range should be unaffected. Proportionally, I have upped the voltage (and power) by 25%, but I would estimate a speed increase of about 19%.

 

[dnmun]

how much did you run the motor with the battery polarity reversed? did you check the voltage on the cells to see how high they climbed?

 

[miuan]

range at 30mph will be getting on for half that at 25mph.

Not nearly as bad, using the simulator revealed 27-28% less range with the same battery, no pedaling. With pedal power it would be between 30 and 35%. That is steady cruising speed however. Stop and go would be a lot worse. With additional 3S battery the effect would be less severe.

 

[monkeychops]

how much did you run the motor with the battery polarity reversed? did you check the voltage on the cells to see how high they climbed?

I didn't run the motor at all with the polarity reversed. Straight after I'd connected everything up (wrongly) and I measured total voltage at 37ish volts, I realised something was wrong and disconnected the paralleled 3S packs. Worried about any damage to my lipos, but have since put them through 2 discharge and bulk charge cycles and they seem ok.

Just to (try to) clarify - I started with a 48V pack (made up of 8 sets of 6S batteries) and connected them in series with a 12V pack (made up of 4 sets of 3S batteries in parallel). I then connected these 2 packs up together in series the wrong way round which oddly (to me) didn't break anything (I hope) but led to a total pack voltage of 37V when I read it with my multimeter.

If I could remember my physics A level I could probably work out what happened. But that was <cough>ty years ago :?

 

[miuan]

Just to (try to) clarify - I started with a 48V pack (made up of 8 sets of 6S batteries) and connected them in series with a 12V pack (made up of 4 sets of 3S batteries in parallel). I then connected these 2 packs up together in series the wrong way round which oddly (to me) didn't break anything (I hope) but led to a total pack voltage of 37V when I read it with my multimeter.

You would've noticed for sure if something happened
The lucky part was measuring the total voltage before connecting the controller.
Not doing so would result in lower speed (36V) and overcharging the 12V pack up to thermal runaway (5+ Volts) long before the 48V pack would run empty (presumably at about 50-60% DOD).

 

[dnmun]

you just never completed the circuit. the reverse battery woulda charged up as the motor ran at low power.

i used to think this would be uncommon and never happen to me. but i did something similar when i attached a single cell charger to a battery cell i was trying to keep above LVC during a battery capacity test. instead i reversed it with 500mA and it went right to LVC. dawned on me pretty quick.

but you have 'no harm, no foul' since you did not charge up the reversed pack.

 

[Jeremy Harris]

I understand what you are saying. In my situation I am being limited by the 22A current limit on the controller. Maximum power on 49V was approx 1078W. Now it is 1342W (obviously depending on battery charge level). But since that extra power has been provided by more batteries of the same capacity in series with the existing ones, the whole pack is still 16Ah total capacity. So range should be unaffected. Proportionally, I have upped the voltage (and power) by 25%, but I would estimate a speed increase of about 19%.

I think you've missed the crucial bit. If you used to ride at around 25mph before, then the average power would have been around 500 to 550W, not the controller current limit of 22A. That's the sort of power it takes to sustain 25mph on a fairly heavy ebike with the rider sat upright on level ground.

If you now ride the same bike at 30mph, then the average power is going to increase to over 900W, just because of the extra speed.

So, you''ve increased the battery pack capacity by 25%, but the average power will have increased by around 80%, so range will drop appreciably, even allowing for the extra battery capacity your range will drop by around 50% or more as a consequence of the additional average power needed to maintain the higher speed. If you don't use the extra speed, but continue to ride at the speed you did before, then range will increase by around 25%.

Hopefully you can see from this that there is a strongly non-linear relationship between speed and power, roughly approximating to a cube law, where doubling speed needs 8 times as much power.

 

[SamTexas]

Hopefully you can see from this that there is a strongly non-linear relationship between speed and power, roughly approximating to a cube law, where doubling speed needs 8 times as much power.

That must be a typo. Doubling the speed quadruples the needed power. But motors lose efficiency at higher speed, so may be 5 times.

 

[Jeremy Harris]

Hopefully you can see from this that there is a strongly non-linear relationship between speed and power, roughly approximating to a cube law, where doubling speed needs 8 times as much power.

That must be a typo. Doubling the speed quadruples the needed power.

Nope. No typo.

The relationship between power and speed roughly follows a cube law, not a square law. Air drag is the major component of bike and rider drag at speed, and aerodynamic drag increases in proportion to the square of speed, so the power needed to overcome that drag is proportional to the cube of speed.

The relevant formulae are:

Aerodynamic drag, D (N) = 1/2 x Rho xCd x A x V², where Rho is air density (kg/m³), Cd is the drag coefficient for the shape of the bike and rider (probably around 0.8 to 0.9 at a guess when upright), A is the projected frontal area (m²) and V is the velocity (m/S)

Power used to overcome drag, P (W) = D x V, where D is the drag (N) and V is the velocity (m/S

Combining those two equations to get power directly we get:

Power (W) = 1/2 x Rho x Cd x A x V³, a cube law relationship between power and speed.

 

[SamTexas]

You're right. I was thinking of the air drag increase. Comment withdrawn.

And that's just theory. In practice when a motor is pushed beyond its limit (40mph or above for a 2807) a lot of power is lost through heat. So a 9 to 10x factor is not uncommon.

 

[Jeremy Harris]

You're right. I was thinking of the air drag increase. Comment withdrawn.

And that's just theory. In practice when a motor is pushed beyond its limit (40mph or above for a 2807) a lot of power is lost through heat. So a 9 to 10x factor is not uncommon.

I agree, it's very likely, as you say, that motor efficiency will reduce a fair bit at higher power levels, making the problem worse.