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Question...

Lets say I have 2 Batteries. 

Each of the batteries has 2 sets of black and red wires. Thicker for discharge (to the motor) and thinner ones for charge (to the power source). 

Battery A is connected to the motor. 

Battery B is connected to the power source.  

Now if I connect one of the battery A charge cables to battery B discharge cables, does this mean that Battery B will charge itself and then battery A?

Then is it also possible to route the power from the regenerative braking back to battery B so not to overcharge battery A?

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  Hi, Jez,

For you quiries, might have several conclusion. A overcharge, B not, AB over charge, B over charge, A not.

Pls forgive me lasy to state other situation. 

Two different solving plan as the picture show. So the finnal answer should have 3X2,6 different defect answer

 

Forgot to introduce my self I'm Bush, Sales from self balance manufactory, and we offer Eco-power for Car brand.

 

Below is serious ~~~~~~~~~~~~~~~~~~~~~~~~~~

The power connection detail is simillar to the power bank.

The power solving problem have been overcome. There is a bettery manage system or called protect board,that make sure the bettery be charge 1 by 1.So there do no have the the situation as you stated, if you do not care about the risk, you can take one pack of the bettery park for more detail.

Any never try the Li bettery for test other situation. (if you insist to do, make sure that you had bought the insurance)

Any quiries, contact me.

 

.566556b884929_Betterymanagesystem.jpg.a5

 

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Maybe i was not clear enough so i will try again. 

Below is the way I have imagined the scenario: 

Mains 240V >> Charger 67.2V >> EUC Socket >> Battery 132W >> Battery >> 174W >> Controlboard/Motor. 

Basically the 132W battery charges the 174W battery like a power bank.

I only ever connect the the 132W battery to the charger.

Once the 174W battery is full it stop charging (overcharge protection will kick in on the BMS).

Once the 132W battery is full then the charger light will go green and both batteries will be charged. 

The option you have presented above has both batteries in parrallel. Because they have their own BMS and are different wattage I am not sure this will work well. 

Also given that each of the batteries puts out between 55V and 67V wouldnt this fry the control board? I dont think it would handle 120+V and would need something to keep it below 67V hitting the board. 

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36 minutes ago, Jez_Fila said:

Maybe i was not clear enough so i will try again. 

Below is the way I have imagined the scenario: 

Mains 240V >> Charger 67.2V >> EUC Socket >> Battery 132W >> Battery >> 174W >> Controlboard/Motor. 

Basically the 132W battery charges the 174W battery like a power bank.

I only ever connect the the 132W battery to the charger.

Once the 174W battery is full it stop charging (overcharge protection will kick in on the BMS).

Once the 132W battery is full then the charger light will go green and both batteries will be charged. 

The option you have presented above has both batteries in parrallel. Because they have their own BMS and are different wattage I am not sure this will work well. 

Also given that each of the batteries puts out between 55V and 67V wouldnt this fry the control board? I dont think it would handle 120+V and would need something to keep it below 67V hitting the board. 

There are a couple of items that I think were left out that may make this clearer.  (I'm not a professional in battery or BMS design)

First, the batteries are rated in Watt hours.  In the example above, a 174 Wh battery is the capacity which is equivalent to the battery delivering a constant 174 Watts over an hour period of time before it becomes depleted.

The charger, which is rated at 132W will charge 132Wh per hour.  So it would take over an hour to charge the battery fully.

The overcharge protection should not kick in if the power supply is working.  The power supply will charge a battery at the max current it is rated for (Constant Current mode of operation) until the battery reaches the rated voltage or 67.2V in the example above.  At this point, it will start reducing current output to maintain the voltage at a constant 67.2V (Constant Voltage Mode of operation).  Once the current output reaches around 100ma or so, the power supply will turn the red charging light green.  The BMS's role in all of this is to balance the individual cells as it charges.  It will only kick in the protective mode if a battery cell voltage exceeds 4.2V indicating a potentially dangerous overcharge situation.  In the example of a 67.2V charger, we can also determine it is designed to charge 16 batteries in series (64.2V / 4.2V per cell = 16 cells).  

You can have as many cells in parallel as you want since it will just increase capacity of the battery pack.  In the 174Wh battery pack, if you put another set of cells parallel to the first one, the battery pack would still be 67.2V but the capacity would now be 348Wh.  The battery pack can be designed with multiple cells in parallel and an individual BMS or you can just connect two batteries in parallel each with their own BMS and the operation would be the same.  The charger would also work exactly the same but the time it takes to charge the pack is now doubled.    

Regenerative power is just turning the motor into a generator and putting current back into the battery.  It will work in the same manner as the charger but it will put larger amounts of current into the battery over a short period of time than a charger by increasing the voltage being generated.

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12 hours ago, Jez_Fila said:

Maybe i was not clear enough so i will try again. 

Below is the way I have imagined the scenario: 

Mains 240V >> Charger 67.2V >> EUC Socket >> Battery 132W >> Battery >> 174W >> Controlboard/Motor. 

Basically the 132W battery charges the 174W battery like a power bank.

I only ever connect the the 132W battery to the charger.

If you look at the schematics of the BMS of the battery packs http://forum.electricunicycle.org/topic/459-electric-unicycles-bms-problem-and-solution/ you will see, that you have no real resistance which could limit the current, if you put the 132Wh battery discharge output to the 174Wh charge input. So if there is some difference in Voltage when you plug the 132Wh battery to the charger input you will fry the plug/wires/some components and/or the overcurrent protection of the 132Wh battery will get activated.

If you put the 132Wh (fully charged) battery discharge output on the charger input of the 174Wh (empty) battery pack you will get some nice fireworks ;) or at least some nice sparks at the charge plug until the overcurrent protection of the 132WH battery BMS gets activated.

Imho the first thing to die will be the voltage inversion protection (which is imho not in every BMS)

Quote

Once the 174W battery is full it stop charging (overcharge protection will kick in on the BMS).

Quote

Once the 132W battery is full then the charger light will go green and both batteries will be charged. 

No. There is no real overcharge protection - you just have an overvoltage protection in the BMS. The "logic" to stop charging is in the charger (it starts with a fixed current until it reaches the max Voltage (67.2) and then it charges with constant voltage until the current drops unter a certain limit)

So the 174Wh and 132Wh will always be on the same voltage level - every minor difference is "immediately" compensated (no current limitation). The voltage inversion protection (if existing) could be a problem here since a diode always gives you a voltage difference.

Quote

The option you have presented above has both batteries in parrallel. Because they have their own BMS and are different wattage I am not sure this will work well. 

This is how all the people are imho doing the battery expansion - putting some batteries in parallel (each with its own BMS). This works fine - you just have to be carefull with the first time connecting the batteries. If the charging state is to different you will get the fireworks again. Could maybe be balanced with an 12V 20W halogen bulb?

Quote

Also given that each of the batteries puts out between 55V and 67V wouldnt this fry the control board? I dont think it would handle 120+V and would need something to keep it below 67V hitting the board. 

If you put the batteries in parallel the voltage stays the same. Only if you put the in serie the voltage gets added.

Another advantage of putting the batteries in parellel (at the discharge wires) is, that you have more battery capacity that can take the power delivered from the motor while regenerative braking.

So putting the batteries one after another (over the charge/discharge wires) brings you no advantage. You also would have to balance the charging state with something like the halogen bulb and after this you should never divide them again. Your main problem here is, that the charge input to the battery pack is designed for 2A/4A and you will constantly be above this limit...

So put them in parellel at the discharge wires should be you way to go. Thats imho "state of the art" around here. Imho the charge wires should not be connected - you just choose one battery pack which is connected to the charger plug.

An interesting thought is, how and if people notice if one of the battery packs in parellel has its overcurrent protection activated. I assume they'll never notice and just carry an usesless battery pack with them....

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Wow. Thanks guys. Well thanks for convincing me that "Daisy chaining" the battery packs not being the right thing to do. 

So perhaps a flick switch between charger input to redirect charge from one battery to another?

 

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30 minutes ago, Jez_Fila said:

...

So perhaps a flick switch between charger input to redirect charge from one battery to another?

 

Imho not necessary - both get charged once the discharge wires are connected.

How did the others do it?

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3 hours ago, Chriull said:

Imho not necessary - both get charged once the discharge wires are connected.

How did the others do it?

So what you are saying is that while one battery charges off the charges the second charges off the discharge of the first but via the discharge wires?

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By the connection of the discharge output both batteries should be charged.

But an answer/tipp from @esajor others who have already done this in practice and gathered experience could be helpful. There are maybe already some discussions regarding this topic around here?

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48 minutes ago, Chriull said:

By the connection of the discharge output both batteries should be charged.

But an answer/tipp from @esajor others who have already done this in practice and gathered experience could be helpful. There are maybe already some discussions regarding this topic around here?

Discharge wires can be used for charging (remember that the motor charges the batteries during regenerative braking), but there's no overvoltage protection on that side (or at least shouldn't be). What I did was make separate branching connectors for 4 battery packs both for charging and discharging:  

Charging port -> 4 * JST-RCY females -> 1 * JST-RCY male (2 pins, so both negative and positive) per battery pack in charging wires.

Battery discharge wires 2 * Anderson Powerpole (1 pin, separate connectors for negative and positive) per battery pack -> 8 * Anderson Powerpole -> 1 * Deans -> mainboard

But these are all internal battery packs.

 

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  • 3 weeks later...
On Wednesday, December 09, 2015 at 0:56 PM, esaj said:

Discharge wires can be used for charging (remember that the motor charges the batteries during regenerative braking), but there's no overvoltage protection on that side (or at least shouldn't be). What I did was make separate branching connectors for 4 battery packs both for charging and discharging:  

Charging port -> 4 * JST-RCY females -> 1 * JST-RCY male (2 pins, so both negative and positive) per battery pack in charging wires.

Battery discharge wires 2 * Anderson Powerpole (1 pin, separate connectors for negative and positive) per battery pack -> 8 * Anderson Powerpole -> 1 * Deans -> mainboard

But these are all internal battery packs.

 

Is this what you did esaj?

20151226_105433.jpg

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5 hours ago, PTrider said:

Is this what you did esaj?

20151226_105433.jpg

Pretty much, yes... although the power for the motor goes through the mainboard. I replaced the original connectors in the mainboard (XT60 -> Deans) and charge port and asked my battery packs to be done without any connectors, then soldered together some adapters (4 * JCY RST -> charge port & 8 * Anderson Powerpole -> Deans) and soldered the connectors to the batteries.

 

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2 minutes ago, Colestien said:

3 in parallel and one in series with them?  Doesn't that put a strain on the bottom one?  It has to "match" the 3 in parallel doesn't it?

I think the "power" here means charging..? So it's 3 battery packs in parallel, none in series. You should never put the battery packs in series (the cells inside each pack are in series, but that's different), as that would raise the voltage too much (around 120V nominal for two 16S-packs in series, 180V for 3...) and you'd just end up breaking you mainboard / motor / something.

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35 minutes ago, Colestien said:

Ok  I misread the drawing.  Sorry I jumped at my first glance.  That's the motor at the bottom.... :blink:.  Sorry, but if I had been right and that was a battery at the bottom.......  

Yeah, easy to misread... not sure what the "power" there actually means, but charging would make sense.

Remember to be careful "playing" around with these batteries, they really, really pack a punch, enough to kill someone. Never connect two or more batteries in parallel unless the voltage in all of them is the same.

Another prime example of what NOT to do is what I did (by accident) yesterday... I was building my motor controller (for a very small 3-phase BLDC-motor, not an EUC motor), and found out that my two 9V rechargeable 200mAh (0.2Ah) batteries in parallel couldn't give out enough power, and would sag down to 3V when driving the motor. But, I have an aluminum-cased step-down converter for bringing voltage down to 12V from 36...72V. So the idea was that I connect the 16S2P-Firewheel pack to it to power the motor. No problem, used a screw-terminal to attach an XT60-connector to the converter and then decided I should check the voltage on the 16S2P-pack. Threw the meter dial to 200V DC -area, and plugged the measuring heads into the XT60-connector of the battery pack. Only problem was, I was earlier measuring currents with the meter, and had left the wire plugged into the current-measuring hole (which has very LOW resistance, unlike the voltage/resistance measuring, which has very HIGH resistance). So, I basically shorted the battery. Lots of sparking for a split second before the 10A fuse on the meter blew and/or the battery BMS cut the power... the end result is here:

MVubVBq.png

That is (was) a solid metal measuring head, maybe 2mm in diameter (a little less than 1/10th of an inch). The head didn't snap or break, it MELTED. The molten shrapnel flying inside the connector actually welded inside the connector, so that has to be replaced. Luckily no further damage than that, but a stupid mistake... sure taught me to be more careful and check the wiring first ;)

 

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11 minutes ago, PTrider said:

Yes, power meant mains plug or charger..

So what would be the safest bet? Completely discharge the batteries begore connecting them in parallel? Or fully charging them before connecting them in parallel?

Either way is fine, as long as the voltage on the batteries is the same before you plug them in. The safest bet is to measure the voltage with a multimeter before doing the connection (and make sure the measuring wire is plugged in the right input, so you don't short it, like I did ;)). If you don't have a multimeter, basic models can be get for quite cheap (20$ or so). If you're really, really sure you want to do it without access to measuring tools, I think the safest bet would be to charge the packs to full (and hope they all are ok and don't have dead cells, so none of them are in different voltages). If you try to first discharge them "completely", they could still have different voltages (and you need to leave the packs alone for a good while after discharging them, as the voltage will "settle" for a while after discharging).

My recommendation would be to measure the voltages and make sure they're all the same. SLIGHT difference (like 0.1V) isn't likely that dangerous, but a difference of several volts causes a very high current to start running through the batteries (only resisted by the internal resistance of the cells) as they try to balance each other out, and will cause the batteries to heat up. If they heat up "too much", the batteries will leak out their electrolyte, and possibly catch fire and/or explode. In a "good" scenario, you just end up with dead batteries. In the "worst" scenario, you just end up dead.

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The weather around here has been so good that I haven't gotten the chance to install my second battery pack. When I do, though, I was planning to bring the two packs close to the same voltage by charging each one fully. If there is more than a half-volt difference between the two I will use a bleed resistor to equalize them. Although if the second pack is really low after a full charge I wonder if it has a problem. Since putting the packs in parallel basically force-charges the weaker pack, they'd better be pretty close already. 

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9 hours ago, PTrider said:

If I understand correctely it is a bit more complicated than that: instead of checking for a voltage difference between the 2 packs you have to check for a difference in voltage between each battery of each pack...

I think that would only be necessary if you get a low voltage reading from a pack after it's (supposedly) fully charged. If the cells are all alright, the voltage of the pack (for 16S pack) should be around 67.2V (4.2V per cell * 16 cells) after charging (it could drop a little bit before settling once you take it off the charger). If there's a large discrepancy between the expected full voltage and the pack, then there's something wrong, likely a faulty cell. In such case, I wouldn't suggest trying to parallel it with another pack, and if you want to fix the pack, then you'd have to start measuring the cells inside the pack to find the faulty one(s) and replace it/them (or have it done for you by a professional, personally I had my custom packs built for me by a single-man company with experience in large pack building & proper tools like battery spot-welder).

@dmethvin's idea of using a resistor between the packs to equalize them is a good one. A power resistor with a few hundred ohms of resistance should be able to clamp down the current between the packs and handle the heat easily without burning. If you have no power resistors, normal resistors could also do, but then you should use probably a large resistor-value just be on the safe side (not overheating the resistor itself) and the balancing of the pack-voltages could take longer.

Gold-Tone-50W-500-Ohm-Aluminum-Housed-Wi

Btw, I have one of these, and I seriously doubt it could handle 50W heat dissipation for any longer time, unless attached to a large separate heatsink ;) 

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@esaj Since you're only dealing with the voltage difference between the two packs, the power isn't too bad. Let's say there's a 10-volt difference between the packs, which would definitely be on the high side if the batteries are both charged in advance. A 100-ohm resistor would see 0.1 amp and only need to dissipate 1 watt. Of course it will take a lot longer to equalize the batteries if they're that far different, so it would be a much better idea to use a charger on the lower one and only do the last volt or so with a resistor. Then you could use a 10-ohm 1-watt resistor!

@PTrider I do have a bit of concern about parallelling two packs with two separate BMSes. The pack I want to add was acting a bit strange and the BMS cut out a couple of times when I had it installed, but I had also accidentally shorted it which probably didn't help. I am hoping that the cells have had time to equalize since then but it is probably worth opening up the pack fully and checking the voltage on all the cells. If the second pack charges to a level more than half a volt different than the first, I was thinking I'd add a high-power diode to the discharge line so that the stronger pack wouldn't overcharge the weaker one. 

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2 minutes ago, dmethvin said:

@esaj Since you're only dealing with the voltage difference between the two packs, the power isn't too bad. Let's say there's a 10-volt difference between the packs, which would definitely be on the high side if the batteries are both charged in advance. A 100-ohm resistor would see 0.1 amp and only need to dissipate 1 watt. Of course it will take a lot longer to equalize the batteries if they're that far different, so it would be a much better idea to use a charger on the lower one and only do the last volt or so with a resistor. Then you could use a 10-ohm 1-watt resistor!

True that, and probably the voltage difference isn't that high (10V), but as "normal" through hole -resistors are usually rated from 1/8 (0.125) watts up to 1/2 (0.5) watts (and some bigger ones up to 1 or 2W, but you can usually tell that from the size of the resistor), I would play it safe and use at least a 100ohm 5W power resistor, even though it's going to take longer for the packs to equalize due to low current. Maybe I'm just overly cautious... :P 

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