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[MrDude_1]

How does zero deal with packs at different voltages?

Lets say for example I have a zero FX, and I put in one fully charged pack, while the other pack is discharged... how does it pull power from both when they're at different levels?
Does it just use the higher pack until it reaches the level of the lower one? If so, doesnt that limit output power to that of a single battery FX until it can use both?

Same goes for the power tank... if its fully charged and the bike is lower... or if the bike is higher and the powertank is not fully charged... how does it cope?

[morimaxx]

Exactly. At a FX with two packs at different SOC (state of charge) you will first use only the one pack with higher SOC until it reaches the level of the second lower pack. From then on you will discharge both simultanous and get higher power to the motor. For the FX Zero recommends to install both packs and charge them together, to get full power from start on.

At models with power tank this will only occur once after installation, as the power tank is fix installed and will always be charged with the other packs.

[MrDude_1]

Thanks, that makes sense.

[Cortezdtv]

I dont think the 2 pack part is correct, if you go out and drain one battery to 50% plug them both in it WILL give you full power.....

Where did you get your info morimaxx?

[Spoonman]

Swapping in or out packs in series won't work - if you wanted to be able to hot swap then the packs would have to be parrallel connected; in such a configuration the only concern would then be control of the initial balancing current between the parallel cells, which is relatively easily controlled.

It's my understanding however that as Morimaxx says, the power tank is a fixed add on, not a swappable item - so it is most likely a series addition to the existing pack and its install will also require reprogramming of the BMS, motor controller and charger as a result, hence the requirement for it to be dealer fitted.

[Cortezdtv]

To get the fx to run in one pack while two are in the bike you would have to install a disconnect switch on the enable wire on the bike side of the connection.... MY 13 and MY 14 use opposite pins for the enable hense why the batteries are not swappable

[benswing]

A Zero SR with a power tank will not run if the battery packs are not at the same voltage.  It will work fine if you charge them up to full charge which allows the charger to balance them.  This happened to me in South Carolina last summer on my 3 country tour.


For the story, start the video at 2:40:

[morimaxx]

Where did you get your info morimaxx?

A FX owner I met some time ago told me about this behaviour.
But I cannot test it by myself as I own a Zero S.

[mrwilsn]

Exactly. At a FX with two packs at different SOC (state of charge) you will first use only the one pack with higher SOC until it reaches the level of the second lower pack. From then on you will discharge both simultanous and get higher power to the motor. For the FX Zero recommends to install both packs and charge them together, to get full power from start on.

At models with power tank this will only occur once after installation, as the power tank is fix installed and will always be charged with the other packs.

This doesn't make sense to me???  Theoretically you could have programming that would allow the use of one battery only until the charge was equal between the two but that just doesn't seem right....however, since you can pull the FX batteries and charge independently I suppose it would make sense that Zero might have it programmed this way.  With a power tank, if the SOC on the power tank is too far off from the other 4 bricks in the monolith then the bike won't work.  Several people have posted about their power tanks getting into this condition.  The solution is to charge up and let the charger balance the cells.

Swapping in or out packs in series won't work - if you wanted to be able to hot swap then the packs would have to be parrallel connected; in such a configuration the only concern would then be control of the initial balancing current between the parallel cells, which is relatively easily controlled.

It's my understanding however that as Morimaxx says, the power tank is a fixed add on, not a swappable item - so it is most likely a series addition to the existing pack and its install will also require reprogramming of the BMS, motor controller and charger as a result, hence the requirement for it to be dealer fitted.

On the S/DS/SR/DSR There are 4 bricks in the monolith wired in parallel (or 3 if you get the smaller battery option).  The power tank gets hooked up in parallel to the 4 bricks.  Each brick will be 116V fully charged.  Reprogramming of the BMS, motor controller or charger is not required to add a power tank.

[Cortezdtv]

On the s all the bricks including powertank will charge and discharge together if they become inbalanced you have the issues that benswing noted above


This is not true of the fx you can put 2 different pack voltages in at the same time but i really wouldnt reccomend it


Ill attach a variety of pictures tonight when get in my computer showing the range in miles when you take packs of different voltages together
It doesnt show power output but you can clearly see it uses both together


I mean tes i can prove it right now but i dont have 3 hands, and  just dont feel like getting on the bikes and doing a brake stand to show peak hp theough the app....screen shot it showing  bike with 2 different battery voltages will read together as "one" and offer you 44 hp not 22

Im sure it pulls more current from the higher energized pack, becuase by the time you take them out or recharge they will be even unless its for very shot time

[MrDude_1]

Well.. lets forget the powertank for a moment, since we're not supposed to be playing with that anyway. lol.

Sticking to the FX, I know each pack is a 28 cell, 27ah (or 25ah) lipo pack with contactor and BMS inside.
The two packs are used in parallel on the bike. This is why you can run it with just one pack if you wanted.


I know if you took two bare packs at different voltages and connected them in parallel, the higher pack would try to instantly charge the lower pack... it would damage the cells.  This is something we have to explain over and over to people with homemade ebikes or RC enthusiasts that want to parallel charge packs.

Now the zero has a contactor, and BMS so it knows the voltages dont match closely... so it can control what happens. I only see 3 solutions possible:

1. it just doesnt work. shuts down.
2. it works off just one pack, until they match. then connects them. This opens up other questions, like how does it know the true state of charge, vs voltage sag?
3. it uses the bms to balance both packs closer... this seems unlikely as its inefficient, complex, and goes against the simple theory zero promotes.

What I was really hoping for, is some new info on how you can parallel batteries with different voltages... perhaps some kind of balancing circuit I was unaware of.

But It looks like its #1 or #2.. and given a choice, I would prefer #2 as long as it also gave info of the situation on the gauge cluster.

[Cortezdtv]

2 batteries both at 65 %





1 battery 65%


Bike battery



91% charge 1 battery in the bike


Now 2 batteries in the cart different charges
1 @ 65% 
1 @ 91%


Equals. Guesses???

[firepower]

My guess it use 91% battery until 65% then switch to use both.
Capacity is shown as average 78%.

Will not be as accurate as showing % single battery or dual battery if same charge.
This is my guess.

[protomech]

I wonder if under high current draw from the higher-voltage/SOC pack, if the voltage sags enough to match the second pack then perhaps Zero will allow the second pack to feed some current in as well.

If the bike still makes full power at 91% and 65% then perhaps this is what is happening; what if you plugged in a pack at 100% and 25%?

My guess is that in extreme cases one battery might be completely disabled, but it might be more flexible than simply disabling one battery until the voltages match.