36v+18=56v would i possibly get 30mph outta this

[jay7264]

I have a 18v 12ah li-ion with BMS also a 36v 15 ah with bms can I series these things up or will the bms's release the magic smoke

 

[docnjoj]

Don't know much about the Magic Smoke issue as I try never to let mine out, but I used to run 54 volts on my trike and the answer to 30mph is yes.
otherDoc

 

[dogman dan]

You would have to stop when the 12 ah pack was empty. I don't think series connecting is a problem with the bms.

In a pinch, you could unplug the 12 ah pack, and limp home on the last 3 ah of the 36v pack.

 

[wesnewell]

The speed will be in relation to wheel size and motor rpm. Use the simulator to determine the speed you will get with your setup.
http://www.ebikes.ca/simulator/

 

[dogman dan]

Since we don't know what you have, it's hard to predict your speed. But 18v should be good for 5-6 mph more than you have now.

 

[jay7264]

im getting the mac pick-n-mix rear geared 26 inch in an evg global frame. the 36v is like 42 when finished charging and my 18v is 21v when finished charging

 

[atom1025]

A 10t mac, 26" tire,at 57v is just shy of 30mph. Maybe 27-29.

 

[jay7264]

im getting the 8t mac. my current setup is some cheopo 250w it takes forever to accelarate but hits 22mph no wind

 

[friendly1uk]

When the 18v pack runs out and opens it's fets, 54v will appear across them.

Might be nothing. I would want to check their spec first though

 

[jay7264]

I ran the 18v pack all the way down and when its dead no power until connected to charger again. Its a 2 green works 20v packs that I'm going to parralell together to achieve 12ah. The BMS on them has separate connectors for charging and discharging

 

[friendly1uk]

I ran the 18v pack all the way down and when its dead no power until connected to charger again. Its a 2 green works 20v packs that I'm going to parralell together to achieve 12ah. The BMS on them has separate connectors for charging and discharging

As the open fets will be by far the biggest resistance in the circuit, they will see full battery voltage. The 18v they have switched off and the other 36v.

 

[docnjoj]

Oh yeah, my 30mph was on a recumbent trike with 9C and 20" wheel @ 54 nominal volts. Would not hold that mph for more that 2 minutes before dropping. This was with rewired Fatpacks.
otherDoc

 

[dnmun]

why not test this theory by measuring the voltage across the mosfets between source and drain?

 

[Pinesal]

Why are you guys trying to go faster than 20mph? That makes your bike not a bike in the eyes of the law.

 

[atom1025]

I often keep pace with road bikes going 30mph. Why not?

 

[Ghost (bike)rider]

Generally speaking, putting batteries with BMSs in series is ok. I have even put them in parallel for increased capacity, but voltages need to be the same.

Just need to remember that when one battery runs out, it will no act as a pass-through - it will go open circuit.

 

[LockH]

"would i possibly get 30mph outta this?"
Not if you visit Canada (and many Provinces) and want to use any roads legally. But it may be that you need to travel long distances in a short amount of time? (Myself, city kid here, so most stuff ain't that far away, plus pubic (sp?) transport available to me if I am really desperate). AFAIK, the faster you can hit anything, the faster one might kill oneself (or others). But suggest you shoot for MUCH faster! But please let us know how things go (if you can still type/use the internet)!
Good luck!
L

 

[dnmun]

why don't you measure the voltage across the output mosfets of the smaller pack when it hits the LVC so we know the answer to that theory? how hard can it be? do you have a voltmeter?

 

[jay7264]

i travel long distances as well as want to be able to keep up with some traffic. i can handle myself at these speeds i use to ride a gsxr 1100 ported polished cammed out jetted 200mph on the clock but i only did 170 on a regular basis.

 

[jay7264]

Well flat out the Mac motor is running on 36v 15ah battery and 25amp controller and it hits 28mph