Is it possible to set up two independent hub motors on a blended two battery system?

[MrTuvix]

Hi all, I have recently set up my bike with two batteries (same voltage and AH) with a battery blender all is working fine. I now want to put a front hub motor on the front fork to create all wheel drive I have good grin torque arms for the project, my question is how can I simply just split the output safely to the two separate system's controller's from the battery blender out to both controller's?

 

[glennb]

You use the word “safely”. What risk are you envisaging?

I don’t know what a battery blender is. I’m imagining a couple of meaty diodes and no load sharing intelligence, but that could be far from the mark.

If the blender is as simplistic as I imagine, then when one battery goes offline the other has to carry the full load of both motors, so whatever combined current draw you program the controllers for you’ll need to ensure that a single battery can supply it. I.e. you cannot safely double the current draw, despite having doubled the battery capacity.

 

[MrTuvix]

Hi a battery blender is a dual battery parallel module for electric bikes designed to increase the current, battery capacity, and discharge capability simultaneously. My one has just one output to a controller so I am thinking of using a xt60 splitter to the power both controller's just don't know how safe that would be electrically?

 

[glennb]

XT60 will do the job if you’re within the cabling’s current limits.

There’s other considerations besides current handling, such as contact resistance, moisture ingress, vibration, and mispluggabity. You could obviously hardwire it to bypass those concerns.

There might be better plug systems. There’s people here with tons of experience with all the different plugs, and the RC crowd seem to be gurus with plugs. It’s not my strong suit.

As to the blender, I remain sceptical. The three claims you made for it don’t address my concerns.

 

[E-HP]

Hi all, I have recently set up my bike with two batteries (same voltage and AH) with a battery blender all is working fine. I now want to put a front hub motor on the front fork to create all wheel drive I have good grin torque arms for the project, my question is how can I simply just split the output safely to the two separate system's controller's from the battery blender out to both controller's?

Yes, it's possible. No, not safely without knowing any information about the motors, controllers or battery.

 

[MrTuvix]

Yes, it's possible. No, not safely without knowing any information about the motors, controllers or battery.

2 x 1000w hub motors, 2 x 48v 13ah batteries (1 × underneath type and 1 × down tube type) controller's x 2 22 amp and 25 amp both can be adjusted

 

[E-HP]

2 x 1000w hub motors, 2 x 48v 13ah batteries (1 × underneath type and 1 × down tube type) controller's x 2 22 amp and 25 amp both can be adjusted

If the combined output rating of both batteries is greater or equal to 45A, and if not, if you can adjust the two controllers to limit the total current to something equal to or below the combined rating (keeping in mind any degradation, if the packs aren't new), then yes.

 

[glennb]

I’d want each of the packs to be able to supply the full 45A.

Unless I’m missing something, that’s the sole point of the battery blender in this application - providing the redundancy of being able to use both motors in the event of one battery going offline.

Keeping front and rear systems independent provides redundancy. One goes down, you’re still running one motor.

With <45A capable packs and a battery blender you lose that redundancy. After one pack goes down you need to disable one of the motors to prevent the BMS in the second pack from shutting down due to overcurrent.

 

[E-HP]

I’d want each of the packs to be able to supply the full 45A.

Yup, I forgot that those blenders don't have any performance benefits.

 

[amberwolf]

Keep in mind that if the blender is there to prevent reverse current from one battery into the ohter, it will also prevent current from the controller to the battery, like if you have any form of regen that happens, either intentionally via regen braking or unintentionally via motor speed going high enough to generate a voltage above battery voltage.

In either case, if there is nowhere for that to go, back to the battery, the voltage can build high enough long enough to damage the controller. It's rare, but it happens.

If your motors are all geared hubmotors or middrive motors, that have a form of freewheel between the motor and the road, then this isn't typically in issue, but with DD hubmotors, it can be.

 

[glennb]

Yup, I forgot that those blenders don't have any performance benefits.

I can’t see much upside of the blender in a dual motor setup, and doubt it’s their intended application, though I’ve given it no real thought, whereas the OP will have.

I like the idea of being able to have a small core pack fixed to the bike for nipping around town, combined with the ability to integrate an additional pack for longer trips (without having to bother about aligning charge states). The redundancy from dual packs is also a benefit for remote adventures.

The ability to detect an absent or offline pack and reduce current in response would be nice, especially for dual motor setups.

 

[glennb]

If your motors are all geared hubmotors or middrive motors, that have a form of freewheel between the motor and the road, then this isn't typically in issue, but with DD hubmotors, it can be.

Agghhh. I know “typically” covers it, but I was still certain you’d elaborate on the subject of seized clutches. You’re still the most thorough replier on the planet, so this one can slide.

 

[amberwolf]

Well, that's a pretty unlikely thing, but yes, it could cause it too.

Honestly from the stuff I've seen around here, and my personal experiences from some years back, it's much more likely to have a broken clutch than a siezed one. (that usually happens from corrosion, which is as likely to destroy the bearings and potentially the motor windings or at least the electrical connections / halls, etc).

 

[glennb]

That’s good enough for me. Sounds like blenders are safe enough with geared hubs then.

(Maybe just me, but the prospect of cascading component failures bothers me. When things fail they needn’t take down other parts of the system,)

 

[amberwolf]

With proper design considerations they won't, but you have to think about how each part works, and how each one can fail and what problems that can cause. Then what each of those problems can cause for other connected parts, and how to choose parts that won't be affected by those problems, or other parts to mitigate them.

Almost always there are ways to ensure a cascade can't happen, but it depends on the budget and the intent whether it's worth doing all that stuff, or spending that much money on the parts to overspec them to the point they aren't susceptible.

 

[glennb]

Yeah, for sure.

I think battery blender functionality needs to be incorporated into controllers.

Votol seem to have, or are planning to have, some form of integrated dual battery smarts.

For all I know, the provided settings might be a placeholder for future firmware releases though, since I haven’t seen it in action or got around to testing it myself. I’ve been hoping someone else would pursue it and I can piggyback on their tests without blowing up another controller.

 

[amberwolf]

I think battery blender functionality needs to be incorporated into controllers.

If they did, then you couldn't use them with regen, by the nature of how those things have to work.

 

[Chalo]

I wonder if all the sudden jabber about battery blenders (not an obviously valuable chingadera) is the result of a barrage of marketing elsewhere, or is the barrage of marketing in itself.

 

[glennb]

Seems likely.

It might be a crude approach, but it does address a need.

The marketing focuses on packs with different series cell counts. I think that’s a mistake. It’s a very niche application, whereas the market for people wanting to pop a secondary “range pack” on their bike is significant.

Many of the higher end road ebikes offer this capability, with water bottle mounted packs to supplement the primary battery integrated in the downtube. I’ve previously wondered how they do it, without taking the step to research it. Does anybody know?

 

[glennb]

If they did, then you couldn't use them with regen, by the nature of how those things have to work.

Yep. Another addition to the long list of restrictions that incorporating regen already imposes.

I’d still like to see it as a feature.