External battery in a backpack

[Guest Philip W]

Hi everyone here in the forum. I am a newbie who purchased a TG F3 264wh around 2 months ago, and I am very happy with it. Just today I opened it up and added a mini voltage meter to it so I can get the real battery voltage instead of 4 lights.

I am thinking about buying an 60v 10a external battery from AliExpress, then connecte this battery's discharging port to my TG F3 wheel's charging port. I know you must rolling your eyes by now. Yeah, I know it's not a safe idea. If there is a difference between these two battery pack it will have a huge discharge and smoke will come out. But still, the convenience of additional range by just adding an external pack to the charging port always fascinate me. I want to to know if this is possible by just some simple electronic modification. Right now could anyone here answer a couple of my questions below. Please forgive my very limited knowledge of electronics.

1. I measured the charging port of the wheel. The pins have no voltages between them. So the BMS must protecting them with diodes. Does that means if the charging port voltage(external voltage) is lower than the battery's voltage, there won't be any current go through because of the diodes?

2. In another post here I learned that I can use a halogen bulb to limit the current between 2 battery packs. Is there other device that can do the same thing without losing so much energy with the bulb?

Appreciate any answer to my questions!

[Chriull]

5 hours ago, Guest Philip W said:

Hi everyone here in the forum. I am a newbie who purchased a TG F3 264wh around 2 months ago, and I am very happy with it. Just today I opened it up and added a mini voltage meter to it so I can get the real battery voltage instead of 4 lights.

I am thinking about buying an 60v 10a external battery from AliExpress, then connecte this battery's discharging port to my TG F3 wheel's charging port. I know you must rolling your eyes by now. Yeah, I know it's not a safe idea. If there is a difference between these two battery pack it will have a huge discharge and smoke will come out. But still, the convenience of additional range by just adding an external pack to the charging port always fascinate me. I want to to know if this is possible by just some simple electronic modification. Right now could anyone here answer a couple of my questions below. Please forgive my very limited knowledge of electronics.

1. I measured the charging port of the wheel. The pins have no voltages between them. So the BMS must protecting them with diodes. Does that means if the charging port voltage(external voltage) is lower than the battery's voltage, there won't be any current go through because of the diodes?

Yes. Your external battery will not be charged by the TG F3, just other way round once the battery back has less voltage (minus the diode forward voltage) than your external battery.

This diodes could be the weak point in your extension - they are designed to "survive" the 2A charge current. If more current flows they easily could get overheat problems.

Quote

2. In another post here I learned that I can use a halogen bulb to limit the current between 2 battery packs. Is there other device that can do the same thing without losing so much energy with the bulb?

The professional solution would be a switching regulator which gives a fixed current of 2A up to the ~67,2V max. So you'd have a portable charger.

If you go with a bulb you should be cautious about the inrush current! The bulbs have normaly a very low cold resistance. So if your wheel battery pack is empty ~(3.3V*16=)53V and you connect it to your external pack you have a voltage difference of ~7V. A 35W/12V halogen bulb should have ~4Ohm "working" resistance - i have read somewhere that the cold resistance can lie around 7% of this "working" resistance. So the inrush current could be around 24A! Once the halogen bulb reaches working temperature the current should be around 1,7A and and 7*1,7~12W dissipation. If the bulb reaches temperature - if not you still have no sufficient current limiting. I'd assume this would need some experiments or detailed data sheets.

 

[Philip W]

Thank you so much for your insight! I will be looking for a switching regulator now and I will report back the result once it's done.

[Chriull]

9 hours ago, Philip W said:

Thank you so much for your insight! I will be looking for a switching regulator now and I will report back the result once it's done.

I'd assume that there is not really something on the market, but maybe with some good luck you could find someting... Imho thats more a DIY thing.

[Philip W]

I found some step-up DC to DC transformer in Amazon which will convert 6-60v to 8-80v and with current regulating for about $21. I think I can use a 36v hoverboard battery with it to output a stable 67v power at the current I want. There will be some power loss due to its 75-85% efficiency but it's a safer way to connect. If the circuit fail most likely it just wont charge the internal battery. Also 36v battery are  popular and cheap.

Now I just wait for the transformer to come in and borrow my neighbour's hoverboad.

[esaj]

On 30.6.2016 at 6:21 AM, Philip W said:

I found some step-up DC to DC transformer in Amazon which will convert 6-60v to 8-80v and with current regulating for about $21. I think I can use a 36v hoverboard battery with it to output a stable 67v power at the current I want. There will be some power loss due to its 75-85% efficiency but it's a safer way to connect. If the circuit fail most likely it just wont charge the internal battery. Also 36v battery are  popular and cheap.

Now I just wait for the transformer to come in and borrow my neighbour's hoverboad.

The step-up transformer is probably a switching type, and stepping up to around double the voltage will likely cause a lot of ripple on the output (voltage oscillation). You can probably smooth it with bypass capacitors, if needed, just make sure they got high enough max voltage (100V caps should work?)... Also, to produce X amps at double the voltage, it will likely draw at least 2 * X amps from the source battery (+ some lost due to inefficiency of the transformer). Do tells us how well it works in the end, if you're going to go through with it.

[Philip W]

9 hours ago, esaj said:

The step-up transformer is probably a switching type, and stepping up to around double the voltage will likely cause a lot of ripple on the output (voltage oscillation). You can probably smooth it with bypass capacitors, if needed, just make sure they got high enough max voltage (100V caps should work?)... Also, to produce X amps at double the voltage, it will likely draw at least 2 * X amps from the source battery (+ some lost due to inefficiency of the transformer). Do tells us how well it works in the end, if you're going to go through with it.

Thank you esaj! I will do this over the weekend.

The transformer just arrived and I kick myself for not ordering the one with LED. It's only $3 more.

Now with a voltage and current meter, I finnally understand the proccess of "fix-voltage/fix-current" charging. Hopefully it will help my little project. And I am glad my TG F3 is indeed a 264wh model.

 

[Philip W]

Ok, guys. Just an update. I built the gig and it passed the initial testings. Now all I need to do is drain the EUC's battery and connect this thing to it.

In the beginning there were sparks every time. I was scared but then realized I should have used a simple switch.

Anyway, tonight I will know if this thing really works one way or the other. If the EUC burns, I can have a perfect excuse to get a much better one.

[esaj]

51 minutes ago, Philip W said:

Ok, guys. Just an update. I built the gig and it passed the initial testings. Now all I need to do is drain the EUC's battery and connect this thing to it.

In the beginning there were sparks every time. I was scared but then realized I should have used a simple switch.

Anyway, tonight I will know if this thing really works one way or the other. If the EUC burns, I can have a perfect excuse to get a much better one.

Double-check the ratings for the wire thickness and the switch, so they don't overheat/melt if the current is very high   A couple of amps should be no problem for most though, as far as I know.

[Philip W]

Thanks esaj, Chriull and everyone reading this thread! This thing works! I ride the EUC to below 60v then connect this to it. It was supposed to provide 66.5v power but due to the current limiting it drops to 61.5 or near. The amperage I carefully tune up to 2 amp and now it works just like the charger. 2 amps only, nothing more. I am curious what will happen when the hoverboard battery's power drop. We will see.

There are some heat coming from the heat sink, not very hot, feels more like warm.

Now the current keep droping but the voltage keep rising. 1.50amp and 64v. Power output drop to 96.6w. I think it's due to the battery power dropping.

I measure the input power. It's about 170w, output is around 150w. So by very rough estimate this thing have an efficiency of 88%. I think I will get another meter to measure the input power vs output power and see the actual number..

 

[Philip W]

Alright guys. I ordered 3 x 158wh 36v hoverboard batteries from eBay. It should give me 474 x 85% = 403wh extra power, combine with my 264wh internal battery, I should have a totally 667wh power. With this I should be able go to 50km distance with some power left. That's around 5 hours riding time. Too much for me already. The batteries will take a long time to come from China. Once everything is here I will finish the project and post it in this forum.

Cost of the project:
Batteries: $160.25, xt60 connectors $7, 42v charger $9.89, voltage converter: $21.49, 3 pin aviation plug $2, Multimeter LCD display $15, bike pouch(hold batteries)$10.5

Total: 226.13

Thank you everyone here for your generous help! Especially esaj and Chriull, you guys rocks!

[alon av]

On 7/3/2016 at 1:46 AM, esaj said:

Double-check the ratings for the wire thickness and the switch, so they don't overheat/melt if the current is very high   A couple of amps should be no problem for most though, as far as I know.

Thanks Philip for your experience with DIY external battery.

Since I can not buy any more the external battery ( shipping limitations ) I am about to copy your Idea.

I bought the 36V battery here( expensive ) and ordered the step up board and a charger.

I have a question though, esaj , you will probably know the answer.

The EUC battery has 2 sets of wires coming out, 1 for powering the wheel and 1 for charging it. The 1 for charging can not have reverse current , it is done with a diode on the BMS board.( I know all this through reading here).

The Hoverboard battery has just 1 set of wires, it performs both power and  charging.

So the question : should I connect the charger directly or should I locate a diode in the charging line?

Any thoughts and advises would be appreciated.  

[esaj]

1 hour ago, alon av said:

I have a question though, esaj , you will probably know the answer.

The EUC battery has 2 sets of wires coming out, 1 for powering the wheel and 1 for charging it. The 1 for charging can not have reverse current , it is done with a diode on the BMS board.( I know all this through reading here).

Yes, there are actually at least two reasons (that I know of) to use separate wiring for charging & discharging in the wheels: The charging-side wiring will go to a different point in the BMS-PCB, that is (or at least should be ) protected agains overvoltage. Another reason is the reverse polarity protection diodes (not all BMSs have these). You can't put the diodes on the discharge side on a device that uses regenerative braking (as that requires the current to flow in opposite direction, ie. back to the batteries).

 

Quote

The Hoverboard battery has just 1 set of wires, it performs both power and  charging.

So the question : should I connect the charger directly or should I locate a diode in the charging line?

Any thoughts and advises would be appreciated.  

If there's only one set of wires, then there cannot be diodes in the path of the current, otherwise the wires could only be used for charging or discharging (the current would only flow in one direction), so probably there are no diodes to locate. I had the not-so-nice "pleasure" last summer to find out that BMSs that have only one set of wires are a bad idea in EUCs: the overvoltage protection cuts the power with full enough pack, because the regenerative braking will slightly push up the voltage, and leads to power cut if the voltage raises too high   Didn't think of it myself, and the guy who built my packs had also no idea, since he had never built packs for vehicles with regenerative braking, only for scuba gear and such

Since you're planning only to use it as "external pack" (at least that's what I've understood), using a single set of wires should be ok as far as I know: even if your original pack(s) wouldn't have reverse protection diodes on the charging side, and would push the voltage above the cut-off value during braking, it should only cut the power on the external pack until the voltage goes back down (but I have no idea what it can do to the boost converter though, never thought or tried what happens if you try to push current to the "wrong" direction through it ).

[alon av]

1 hour ago, esaj said:

 

I will be using it as external pack extending my range around 8 Km ( hopefully )

I am thinking what will happen if I charge the battery and then disconnect the 220V charger input.

Could the battery shortcut through the charger causing damage or fire ?  

[johrhoj]

Maybe this is a problem (tell me if i'm right or wrong here)

With a full internal battery, going downhill, the power generated by the EUC must be dissipated. If it cannot charge the external battery, then the use of an external battery is dangerous, because the external battery will keep the internal battery charged to full. Going downhill will cause heating problems and possibly damage the internal battery. 

Connecting the external battery should be done by placing it parallel to the internal battery, while having a circuit for balancing the consumption between the two. 

Another option may be by activating the external battery after having used to the internal battery to 50 %. 

I am not an expert. I asked the customer service of Ninebot if I could use an external battery via the charge port. The answer was that they do not sell external batteries and that this use is not intended, and that I should not use third party batteries to this purpose. 

[alon av]

Hi johrhoj

Because of the step up board you have a point here  . it might be that the board voltage output is constant and not proportional to the external battery voltage level. 

  In that case maybe I should fix the output voltage around 60V and not 67V , when the battery is full it will not charge, and like your second option , at about 60V (~50%) it will start charging untill the external battery BMS will reach low voltage cut off.

If by going downhill the inner voltage will go higher then 60V charging will stop.

 

 

[Chriull]

7 hours ago, alon av said:

...

I am thinking what will happen if I charge the battery and then disconnect the 220V charger input.

Could the battery shortcut through the charger causing damage or fire ?  

As it seems that you have a

On 29. Juni 2016 at 6:13 AM, Guest Philip W said:

...

1. I measured the charging port of the wheel. The pins have no voltages between them. So the BMS must protecting them with diodes. Does that means if the charging port voltage(external voltage) is lower than the battery's voltage, there won't be any current go through because of the diodes?

...

reverse voltage protection diode in the charging part, nothing can happen (if the charger does not misbehave and deliver too much voltage) - but with the diode its short circuit proof!

6 hours ago, johrhoj said:

..., because the external battery will keep the internal battery charged to full. Going downhill will cause heating problems and possibly damage the internal battery. 

...

Thats a great input! Normally the charging from the external battery is slower than discharging by riding the wheel (riding on a leveled straight needs about 2-300 W (for a ninebot e+ near tiltback), charging can only deliver at a maximum 67Vx2A~130W less the losses from the step up converter and less the "charging efficiency" - so normally the battery should get nicely depleted - but going down for a longer distance or starting with a fully charged battery and the external battery attached could lead to problems. Unfortionatelly there will be no warning and no damage to the internal battery, but the rider will take the pain! The battery is protected by the BMS, which will cut off and leave the driver faceplanting.

 

5 hours ago, alon av said:

Because of the step up board you have a point here  . it might be that the board voltage output is constant and not proportional to the external battery voltage level. 

? I can't follow you with this thought?

if the external voltage is lower than the internal, than the internal will just drop over time with the burden and regenerate a bit wirhout any significant burden.

if the external voltage is higher, this will push up the internall voltage by charging, but since the external is not really strong (2A limit) the external will drop voltage quite fast while there is load on the system...

5 hours ago, alon av said:

  In that case maybe I should fix the output voltage

The step up converter really has a max voltage and a max current (you measured the no load voltage and its really limited to the max you choose?) - then i think i like this thingie ?

5 hours ago, alon av said:

around 60V and not 67V , when the battery is full it will not charge, and like your second option , at about 60V (~50%) it will start charging untill the external battery BMS will reach low voltage cut off.

I'd guess the charging will step in to late when you start at 50%. At 50% 264Wh batteries start to get "dangerously low" and additionaly don't forget the 0.7-1V diode loss! Normally it should be more than enough if you leave 1-2v margin. Just if you have long declines at the beginning of your travel you shold set a bigger margin. Or to be flexible and on the safe side make a switch, which you turn off before longer declines (in the beginning or whenever you have the feeling the battery could be about full)

5 hours ago, alon av said:

If by going downhill the inner voltage will go higher then 60V charging will stop.

Imho regenearative breaking is extremely inefficient and only causes shutoff with very very fully charged batteries. But thats my imho against your faceplant - so your decision!

 

[Scully]

Here's another idea relating to 'extra battery in the backpack'
(I haven't read the whole thread)

Would it be possible to re-route the battery inlet cables? 
For example, if you cut and extend the current cables you could then move them outside of the leg pad. 
If the join to the main battery is accessible - once the main battery is flat, you simply dis-connect it and re-connect a battery from your back pack. 

The problems.... 

1, You'd need to find a way of making the joins waterproof, 
2, If you had a sudden 'jump off' your wire would get caught - so it would need a quick release. 
3. If you had a quick release, you'd be in danger if it became dis-connected whilst you were riding. 

Perhaps not such a good idea after all.

[alon av]

9 hours ago, Chriull said:

As it seems that you have a

reverse voltage protection diode in the charging part, nothing can happen (if the charger does not misbehave and deliver too much voltage) - but with the diode its short circuit proof!

 

Thanks Chriull .

The hoverboard battery has no reverse voltage protection.

[Chriull]

18 hours ago, alon av said:

I will be using it as external pack extending my range around 8 Km ( hopefully )

I am thinking what will happen if I charge the battery and then disconnect the 220V charger input.

Could the battery shortcut through the charger causing damage or fire ?  

 

6 minutes ago, alon av said:

Thanks Chriull .

The hoverboard battery has no reverse voltage protection.

With the diconnected charger at the battery you meant the external one?!

Normaly a disconnected charger makes no short circuit - or at least should never to. You can measure that wirh an amp meter in one line, if you don't trust your charger.

the chargers normally could have a filter capacitor at the output - his losses get loaded by the battery, but that should be minimal.

[alon av]

10 hours ago, Chriull said:

 

? I can't follow you with this thought?

 

I was not clear enough .

Using the step up board is different from a parallel external battery because it's voltage stays the same ( maybe) . Normally I have some flat ride before going down so in case of parallel batteries , both will deplete a little before going down and while going down only the inner battery will gain charge.

With the step up board , set to 67V, it will keep on charging before and through going down .

I was compering it in my mind to parallel battery until johrhoj  remark     

[alon av]

10 hours ago, Chriull said:

 

 

 

I'd guess the charging will step in to late when you start at 50%. At 50% 264Wh batteries start to get "dangerously low" and additionaly don't forget the 0.7-1V diode loss! Normally it should be more than enough if you leave 1-2v margin. Just if you have long declines at the beginning of your travel you shold set a bigger margin. Or to be flexible and on the safe side make a switch, which you turn off before longer declines (in the beginning or whenever you have the feeling the battery could be about full)I

 

I will have a switch, also for connecting it to the charge port while switched off and then switch it on.

So setting the external pack to 64V sound good ?   

[Chriull]

12 minutes ago, alon av said:

... Normally I have some flat ride before going down so in case of parallel batteries , both will deplete a little before going down and while going down only the inner battery will gain charge.

...

 

7 minutes ago, alon av said:

I will have a switch, also for connecting it to the charge port while switched off and then switch it on.

So setting the external pack to 64V sound good ?   

I'd go with the ~67V - with the diode voltage drop the internal battery so will only get charged to somwhere around 70% maybe.

and for the first part of your travel with full battery i'd leave the switch off. Just after the decline i'd switch on the external battery.

[alon av]

1 minute ago, Chriull said:

 

I'd go with the ~67V - with the diode voltage drop the internal battery so will only get charged to somwhere around 70% maybe.

and for the first part of your travel with full battery i'd leave the switch off. Just after the decline i'd switch on the external battery.

Will do  thanks

Now I have to wait to get all the orders, may take a month to arrive from china 

[Philip W]

Completely agree with Chriull, I am waiting for batteries to com from China. It will take 1-2 months. Once it's here I will set the output to 66.6v, just to be safe and evil. The whole idea is that I dont need to open up the EUC or switch batteries. I just keep it plug-in and it will charge it safely as I go. And I can also use it in other EUC without any mods.

The regen increase is very small, even after long decline it will go up 1v max. So I am not worrying about it.

The little board can set both voltage and current limit. 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.