E+ powered by A123 20 Ah pack UPDATE

[jerome_speedy]

I definitely want two batteries to be used at the same time: first of all, with two batteries in parallel, the intensity will be divided by about two (when both batteries voltages are identical).
Secondly, I need the hub battery to be active, otherwise the TF controler goes to sleep after 10 mins (or so i've heard).
Thirdly, without the hub battery, the original controler is useless. In my configuration, I hope it'll be able to continue showing the remaining charge.

As for mixing voltage, the MBR3060 double rectifier should take care of any potential damage.

 

[ambroseliao]

a simple rectifier won't balance the mismatched chemistries nor the different discharge/charge rates nor the different max and min voltages of the packs when they are in parallel. If you are running a 48v battery with a 36v system, you'll overdraw the 48v battery below its safe specs since the low voltage cutoff is 30v with the Tidalforce bike.

 

[jerome_speedy]

a simple rectifier won't balance the mismatched chemistries nor the different discharge/charge rates nor the different max and min voltages of the packs when they are in parallel. If you are running a 48v battery with a 36v system, you'll overdraw the 48v battery below its safe specs since the low voltage cutoff is 30v with the Tidalforce bike.

Ah oversight from my part... You're damn right. But since I'm a little stubborn, I'll try what I said anyway I'll just make sure I don't go to the last drop of energy in the batteries and hope for the best. I can also install a voltmeter to monitor the state of the 48V battery.

 

[ambroseliao]

You will destroy the 48v battery in short order. The LVCO for the 48V pack is at the HVCO of the 36v battery.

48v battery range is 54v HVCO fresh off the charger and 42v LVCO.

The working voltage range of the Tidalforce battery is 42v fresh off the charger to 30v LVCO.

You'll be damaging the 48v battery as soon as you start drawing power from it when on the bike. Also, If your rectifiers fail, you will damage the Tidalforce front hub battery with high voltage. DAMHIKT.

You can be stubborn or you can be smart and just save the 48v battery for the next bike project or sell it.

 

[jerome_speedy]

Erm, Ambrose you make a valid point about not trying to push the LifePO4 battery below its limit.
To address this problem, first, I thought about using some circuit with a zener, a resistor (to be calculated) and a mosfet to cut the lifepo4 before it reaches the LVCO.
Then I thought that the BMS (not seen on my schematic but which will be present) would take care of disconnecting the LiFePO4 battery before it's dangerous for it (is that correct ?).

As for the double rectifier failing, I don't see a problem with that. When they fail, the diodes are open circuit not closed circuit. I don't see any danger coming from that. I repaired a switching PSU from an old computer of mine (which used a cousin of that MBR part), replaced the MBR and got the thing working fine afterwards (and no damage was done to other parts around by the MBR death). The failing MBR had on open circuit diode on one side.

So practically speaking, I don't see any problem using the 48V battery and the 36V hub battery.

However, I read that some PWM circuits are not appropriate for brushless motors. I need to investigate what else could be done to replace the PWM circuit I had in mind. I also need to find one that takes more than 52V as input so that it works with a fully charged lifepo4 pack.

 

[ambroseliao]

So practically speaking, I don't see any problem using the 48V battery and the 36V hub battery.

I've tried to point out problems with your idea. You are overestimating what your simple circuit can do. If your LiFE pack has a BMS, then it will cut off the power to the bike in short order because you are using it below the LVC of the BMS for the pack.

A word to the wise should be sufficient. You don't have to believe a word I say. Best of luck to you. :|

 

[dnmun]

if he connects the 48V battery to a 36V battery then the output of the 48V battery will appear shorted to the BMS as the current rushes out to the short and the BMS will immediately turn off the output so it will never discharge the 48V battery. of course he could just bypass the BMS and blow up both batteries at the same time. maybe he needs to learn things this way.

 

[jerome_speedy]

Hi,

The keyswitch from my tidalforce doesn't work anymore since I use an external battery (this is a known, documented "bug"). I want to use a keyswitch to disable the controler when I'm away from my bike, how do I do it ?

On the "Everything Tidalforce" website, does anyone know where is coming the power to the controler PCB, so that I can use a keyswitch like before ? Thanks