External battery in a backpack

[alon av]

1 hour ago, Philip W said:

Before you buy it make sure it has the current limit function, or you will get a 10-15 amp rush. It will do some damage. The board comes with no manual, but their website's forum gave me the instruction how to adjust it. Please read those instruction before you connect it to your EUC. Too many people complained in Amazon without knowing what they were supposed to do.

I saw your pictures and bought the same board

If it works so nicely for you it will also work for me, I guess 

[Philip W]

Just want to make it really clear for this board: turn the potentiometer for the CC counter-clockwise at least 20 circles to make sure it's set at the the minimum. Then connect the EUC and turn it up by clock-wise. Don't turn it too fast as you will see a jump in the current at some point. Over-current could damage your BMS or burn the wire.

[esaj]

One way to setup the maximum amperage correctly is to use a large power resistor or Kanthal/Nichrome (heat resistor) -wires as load and a multimeter in series. Use low voltage to limit the power dissipation in the resistor (assuming the CC-setting stays the same regardless of set output voltage, haven't actually tested on mine).

If it's this boost converter: http://www.aliexpress.com/item/High-Efficiency-95-DC-DC-600W-IN-12-60V-OUT-12-80V-Boost-Converter-Step-Up/32374850067.html  do not try to adjust the voltage to very high values without any load, on mine, the voltage raised to almost a 100V with only the multimeter (measuring voltage, ie. high resistance) as load, and it wasn't even at the end of the trimmer at that point. The output-side capacitors are 100V max (on mine at least), so they could blow up if the voltage raises too high

 

[Philip W]

21 hours ago, esaj said:

If it's this boost converter: http://www.aliexpress.com/item/High-Efficiency-95-DC-DC-600W-IN-12-60V-OUT-12-80V-Boost-Converter-Step-Up/32374850067.html  do not try to adjust the voltage to very high values without any load, on mine, the voltage raised to almost a 100V with only the multimeter (measuring voltage, ie. high resistance) as load, and it wasn't even at the end of the trimmer at that point. The output-side capacitors are 100V max (on mine at least), so they could blow up if the voltage raises too high

 

That's exactly the converter, though I paid $21.5 for it. ?

Now I see another one with good promise. http://m.aliexpress.com/item-desc/32335824207.html

It comes with LED to adjust things digitally, and will show many info including the input battery power level. Love what the thing can do.

[Philip W]

Here is a little update,

The 3 36v batteries are still on the way. Today I put my neighbour's hoverboard battery and the other stuff in the bike pouch and went out to test the range.

It almost felt like torture. My feet hurts from standing for just 20 minutes. I circled Flushing Meadow Lake 9 times, each round is roughly 2 miles. After 3 hours of riding, rest then riding again, the EUC finally flashing lights at 18.5 miles. The hoverboard battery contributed 117wh of power during the first 55 minutes. It was a little disappointing because I was expecting 134wh, not 117. The boost converter's efficiency is too low. I think maybe in the future I will connect 2 36v batteries in serial then use a resistor to lower the voltage. It might work better this way.

Nonetheless, it's quite impressive that my EUC now can go 18.5 miles. The 36v battery add a 5-6 miles to the range.

[Chriull]

3 hours ago, Philip W said:

...Today I put my neighbour's hoverboard battery and the other stuff in the bike pouch and went out to test the range.

It almost felt like torture. My feet hurts from standing for just 20 minutes. I circled Flushing Meadow Lake 9 times, each round is roughly 2 miles. After 3 hours of riding, rest then riding again, the EUC finally flashing lights at 18.5 miles. The hoverboard battery contributed 117wh of power during the first 55 minutes. It was a little disappointing because I was expecting 134wh, not 117. The boost converter's efficiency is too low.

You used one 158Wh 36V battery pack and you expected 134Wh used for recharging (85% efficiency of the DC/DC converter) and only got 117Wh contributed within 55 min.

So 117Wh in 55 min are an average power output of ~127W. With the ~85% efficiency the hoverboard batterie would deliver ~150W. With 36V that means an average current of 4,2A! At these currents nowadays top 18650 cells loose quite some of their nominal capacity!

This effect (the higher the continous current, they lower the usable capacity -> https://en.wikipedia.org/wiki/Peukert's_law found by @Jason McNeil ) was discussed in the below linked thread. Unfortionately the numbers wrong - dampfakkus.de has some probs with their charts...;( - but it should give a "feeling". Real usable capacity should be higher:

3 hours ago, Philip W said:

I think maybe in the future I will connect 2 36v batteries in serial then use a resistor to lower the voltage. It might work better this way.

Imho not the best solution, so which better solution could exist for you:

- Your wrote that while driving 3 hours the external battery pack contributed for the first 55 minutes. So you could reduce the output current of the DC/DC converter by something like 1/2 to almost 1/3. That would reduce the average current taken of the external battery pack and should increase his usable capacity.

- once you get more packs put them in parallel (be carefull that they have about the same voltage before connecting them together!), so the load for each gets less ( 1/2 with 2 packs in parellel, 1/3 by 3 packs in parallel). So once you have your 3 packs the average current with your by now used setup should be a bit above 1A and greatly increase the usable capacity. Maybe you then can finetune the "efficiency" by reducing the output current of the DC/DC converter a bit - depending on the batteries characteristics.

3 hours ago, Philip W said:

Nonetheless, it's quite impressive that my EUC now can go 18.5 miles. The 36v battery add a 5-6 miles to the range.

If you take the nominal capacity of your TG F3 wheel (264Wh) and the nominal capacity of the hoverboard pack you get to an ratio of 264 Wh :158 Wh = 63%:37%.

Now the ridden distance: 13,5 miles :5 miles = 73% : 27% or 12,5 miles : 6 miles = 68% : 32%

If you compare these ratios the efficiency of the external battery compared to the internal battery is not too bad - imho with reducing the current per pack you could maybe reach the same ratio as the ratio of the nominal capacity.

 

 

 

[esaj]

6 hours ago, Philip W said:

I think maybe in the future I will connect 2 36v batteries in serial then use a resistor to lower the voltage. It might work better this way.

Careful with this setup. I could be wrong, but the problem I see with this, is that if the 72V battery packs (2 * 36V in series) and the internal pack are at full charge, the resistor will only limit current between the packs, but it won't stop the internal pack voltage from raising above the maximum of 4.2V per cell (67.2V for 16S pack), as the circuit will try to reach equilibrium (same voltage on both sides of the resistor). If for any reason the BMS overvoltage protection fails or there isn't one in the BMS, it will overcharge the internal pack, and damage the cells (or even overheat them and cause them to catch fire, or worst case, explode).

Also, depending on how much voltage difference is there between the packs and how large resistor you're using, the power dissipation in the resistor could get very large. Just as an example, if the voltage difference was 5V and you'd have 10 ohm resistor, the current would be

I = U/R = 5V / 10ohm = 0.5A

But the power dissipation will already be:

P = U*I  = 5V * 0.5A = 2.5W

2.5W might not sound much, but it will already heat up a metal-cased power resistor considerably. Plus, If you'd have the 10S (36V nominal) packs in series at full charge, the total voltage would be:

4.2V * 20 = 84V

Even if the internal pack would be full at 67.2V, the voltage difference is already:

84V - 67.2V = 16.8V

Now, still using the same 10 ohm resistor, the current will be 1.68A (16.8V / 10ohm) and the power dissipation will be 28.224W (16.8V * 1.68A). That's going to probably need a heatsinked power resistor, even the ones pictured here (50W and 100W) aren't good for but maybe 1/10th or 1/5th or something like that of their maximum wattage without a large heatsink:

 

[Philip W]

Thank you both @Chriull and @esaj !! From now on I will lower the power to 2A instead of 4A. I had no idea of that battery effect until now. So I did a little experiment. I charged the hooverboard battery to full again then use it to charge the no-power EUC, but this time I measure the input power. The hooverboard gave out only 126wh of power! So it appears that the dc booster's efficiency is 117/126= 93%! But actually it should be lower because in the park I kept stop and resting so the pack had lasted longer, so it released a little more power. In short the real efficiency ratio is between 92% and 85%. It should be closer to 92% because 85% was a rough estimate while 92% is measured by the meter. The metal container of the booster was not hot either, so it's proof that not much power was lost to the heat.

esaj, thank you. I didn't realize the overcharge problem with resistors. Yeah, that's a bad idea, which will give me plenty of face plant. Now with the new data I am happy with my setup. Only that I don't want to do a 3 hour riding any time soon. And my external battery pack will be 4 of 36v, no more. 6 hours of riding will be a painful torture ride for my EUC. 36-40 mile is really far already. My next EUC will be faster and have a seat.

[Philip W]

Now finally the batteries arrived. I put them in my bike pouch but the booster have nowhere to place. I tried different ways to hold the batteries and the booster. In the end, I used a hydration pack. It's much easier and cleaner. The hydration pack can also used to hold drinking water. Very useful for long time riding.

I put 3 of them together. Each can go 6 miles so the total distance should be 6x3 + 12 = 30 miles.

I am going to try it tomorrow and see if can really go 30 miles.

[Hunka Hunka Burning Love]

Is it just me or does that look somewhat like an explosive device with an old style TNT plunger (trolley handle) with detnation cable leading to 3 packs of C4?   Just be careful not to roll too close to any embassies or police gatherings...

[Philip W]

Haha! When you're thinking about bombs and guns, everything looks like it. So I am basically riding a bomb with a backpack of C4s to a park and hopefully someone will stop me from a Lithium explosion. Dang that's really funny! I want to scare the shit out of park rangers.

[Chriull]

27 minutes ago, Philip W said:

Haha! When you're thinking about bombs and guns, everything looks like it. So I am basically riding a bomb with a backpack of C4s to a park and hopefully someone will stop me from a Lithium explosion. Dang that's really funny! I want to scare the shit out of park rangers.

Lets hope that their scanners did not get triggered by your keywords and homeland security is preparing to take over your house...?

[Philip W]

Man! What a disappointment! 3 batteries can only output 216wh of power into the EUC. I was riding in a huge circle, from Howard beach through bike tails along belt parkway to rockawy beach. It was only at half of the circle the 3 batteries shuts down. I was lucky to bring my neighbour's hooverboard battery along. That thing uses Samsung cells and gave me 117wh of power alone. With that battery and the remained power in the EUC I finish the big circle and made it back to my car.

The lesson is: never buy those cheap $50 hooverboard batteries. It was so obvious now I see me being idiotic to trust them.

The backpack is actually not feeling heavy, because I didn't move much and the wind cooled me down. My feet were burning them numb from all the riding. Children were curious around me and some even said "cool, I like that!" I generally smiled back and waved.Only one young man who was waiting for a bus yelled, "GET A BIKE!" Man! I didn't expected it so I just passed him. Now I think I should have yelled back, "GET OUT OF YOUR CAVE. It's 2016 already."

[Pingouin]

9 minutes ago, Philip W said:

never buy those cheap $50 hooverboard batteries. It was so obvious now I see me being idiotic to trust them.

The backpack is actually not feeling heavy, because I didn't move much and the wind cooled me down. My feet were burning them numb from all the riding. Children were curious around me and some even said "cool, I like that!" I generally smiled back and waved.Only one young man who was waiting for a bus yelled, "GET A BIKE!" Man! I didn't expected it so I just passed him. Now I think I should have yelled back, "GET OUT OF YOUR CAVE. It's 2016 already."

Hoverboard batteries that are not marked, should be used with caution as they are the ones that can catch fire (faulty or no BMS), unlike the new samsung ones, but I didn't know they reduced the range, it's true that with a hoverboard it's hard to evalutate the practical distance are they are mainly used in parks, the front of the houses, or inside ^^

As for the guy taking the bus and saying "get a bike", you can respond "get some foots" or "where is yours" ^^

[Philip W]

@Pingouin I believed that the fires were not caused by the batteries but other factors in a hooverboard. When I opened my neighbour's, I found small pieces of aluminum inside. They must be the result of clumsy manufacturing. I can imagine what could have happened if those small pieces of metal ended up on the circuit board, shorting the sh*t of it. All it takes is charging the board upside down and a little bad luck. The batteries themselves should be much safer. During the whole day I kept checking their temperature. They were just slightly warmed. 

That guy is very rare in my opinion, most people I met along the way just being bewildered or confused.

[Pingouin]

I'm not so sure, I've looked at alot of videos on the internet, and opened mine, it seems that most fires were triggered by overcharging, or too much power asked from the batteries, and it is the BMS which is supposed to handle these issues, so I'm pretty sure it's a battery problem.

I wouldn't be be at ease with a battery like this in my backpack, it's very unlikely there will be a pb, but who knows ^^

 

[Philip W]

@Pingouin what I understand about BMS is, yeah, it's supposed to protect the batteries from over-charging. So it is the charger. The charger can only go up to a certain voltage then it shuts down when the batteries reach that level. In order to have an overcharge problem you need both of them malfunction: BMS and charger. I think that chance is very slim. That's why we have so many things with Lithium batteries but it seems only hooverboard got a bad reputation of burning. I think the manufacturing of hooverboard is the big problem. They have big pieces of metal inside the board and didn't spend time to clean them up. So when hooverboards hit something on the road, the small pieces of metal got dislodged and flying inside the enclosure with the circuit board. It becomes a even bigger problem when the board is up side-down. The little pieces of metal will land randomly somewhere on the circuit board. This way a disastrous burnout will happen, sooner or later.

It's very strange that most of the Internet thinking the cause is something sharp inside pierced the wrap and make it burn. I don't think think that's the majority of the cause. Just open one up and you will understand how hard it is for that to happen.

[Pingouin]

It's not a faulty charger and a faulty battery, because in a li ion battery, there are several cells (16 in a EUC battery for example), the BMS's role is to avoid under voltage and over voltage, but also and mainly to balance the cells, which means to equily charge them. But if, during the charge, the BMS doesn't do it's job, one celle might get overcharged, start heating and catch fire, then burning the others at the same time even though the charger didn't detect anything wrong as it only detects the total voltage of all the cells, and not individualy.

I've looked in the hoverboard, I didn't see this sharp metal piece, it's true that if a conductor lands on the circuit, it might create a fire, but I think the main problem is the battery itself.

[Chriull]

Plus the main "thread" by the above mentioned reason comes to effect by the use of bad/reused battery cells and the high volume of generic hoverboards with these bad cells shipped.

 generic EUCs with bad/reused cells could/should be as dangerous - imho the reason (?almost?) nothing happened till now is just the lower volume. And that many riders use brand EUCs with good cells.

We'll see if and how this changes, once the battery cells reach the end of their lifetime...

[Philip W]

I agree that if BMS malfunction this way, the battery will burn. That's why I always charge my hooverboard batteries in a metal pan. If it burns the fire won't spread. After the charging they should be considered safe, as long as I don't punch them or drop them. I heard and saw videos about Li-Ion batteries burns while charging, but yet to see one burn by itself or under normal discharging. So I am confident that my setup is safe.

Only thing is that now I have to buy hooverboard batteries again. This time good quality ones. 

[1kw]

yep buy good batteries first time around. Im looking at maybe the 16000mah hobbyking lipo packs. get 4 * 4 16ah packs for 16s16000mah... 947wh.

[Philip W]

On August 9, 2016 at 7:57 PM, 1kw said:

yep buy good batteries first time around. Im looking at maybe the 16000mah hobbyking lipo packs. get 4 * 4 16ah packs for 16s16000mah... 947wh.

Wow! With that much power you can go really far (50 miles+). It's painful for me to ride just 20 miles.