Dual Battery Balancer circuit - experiences!

[Ravi Kempaiah]

Public Safety Announcement (PSA):

The dual battery function is a favorite among many riders, and being able to connect 2 batteries and extend the range is an excellent feature. This is one of my favorites too.
Bosch has implemented this in an excellent manner, and it works very well. But, I wanted to share our experience with some of the dual battery balancer circuits we have had. This was mainly intended to be used on hub-drives.

Early this Spring, we were testing a dual-battery balancer module using two 52V batteries, and this electronic piece caught fire.
I am so glad that the battery was not affected, but it burnt the battery base. Since then, we have been wary of dual battery balancers because the QC can vary widely and you need to have done your due diligence before using something like that. One fire can ruin all the fun. At least make sure that the dual battery module has UL-certification.

Until we are confident of long-term safety, on most of our bikes with hub drive or custom mid-drive, we will only offer single battery versions. We were lucky that this incident did not happen with any of our customers, and our testing efforts helped us identify this issue.

So, the takeaway is, if you don't know the source and don't have full engineering details of the wiring and electronics, be very cautious using dual-battery module with high-voltage batteries like 52V. If you have positive experience with dual battery modules on hub-motor bikes, please do not hesitate to share.

Some pictures of the incident at our facility.

Burnt battery balancer module.

Semi-burnt battery base

Our testing area after using the fire-extinguisher

Another sample we are testing, and we have a few samples like this.

 

[Gionnirocket]

Something such as this needs to be constructed with only the best quality components.
I've seen many of these on Amazon, eBay and Ali and have never felt confident enough to purchase.

Of the units that you are testing.. are they paralleling the batteries or switching between as the voltage drops?

 

[fooferdoggie]

ya too bad you canto do it like bosch just sip form each one one at a time.

 

[Ravi Kempaiah]

ya too bad you canto do it like bosch just sip form each one one at a time.

We will have to engineer a solution like that, and it can be done, but it would cost $500K to get this into production. Bosch has done an excellent job!

 

[6zfshdb]

Thanks for posting this Ravi, it confirms my decision to eliminate my battery isolator.

I've been using this unit:

Amazon.com

Although I haven't had a fire, I did notice the case got quite warm, almost too hot to touch. Out of caution, I replaced it with a simple DPDT switch to change between batteries. Generating that much heat also wastes energy.

I also found it was more convenient to use the switch since I can better control the charge level in each battery individually. I don't have to recharge both after a short ride where only one battery was necessary.

Thanks again.

 

[Tom@WashDC]

Thank for the post Ravi. I'll let you know how mine works. Running 2 X 48V batteries. I check the temp by hand every now and then.
I did look at every version I could find on the web, and read reviews. They seem to be purveyed all over the place. I did not find any reviews claiming the unit burnt up, or caused a fire. There is always a risk buying such items out of China, as they may not have the same concerns, regulations, or liability at this time for the safety of their products.

Have you looked at this unit? Seems to be a bit more sophisticated?

DATEx2 Parallel Battery Adapter - Big Game Bikes

Upgrade your eBike journey with the DATEx2 Parallel Battery Adapter – the 'battery blender' for seamless rides. Connect up to three batteries, handle diverse types, chemistries, and charge states. Say goodbye to inconvenient swaps! Voltage range: 24V to 84V.

biggamebikes.com

 

[Gionnirocket]

Thanks for posting this Ravi, it confirms my decision to eliminate my battery isolator.

I've been using this unit:

Amazon.com

Although I haven't had a fire, I did notice the case got quite warm, almost too hot to touch. Out of caution, I replaced it with a simple DPDT switch to change between batteries. Generating that much heat also wastes energy.

I also found it was more convenient to use the switch since I can better control the charge level in each battery individually. I don't have to recharge both after a short ride where only one battery was necessary.

Thanks again.

Much safer solution and as you say, much better control for those that have a clue of what they want and how.

These claim to be paralleling... but I'm thinking that's just in connection and that in use it's one battery then the other as voltage drops. If I'm assuming correctly then for sure I'd opt for a switch if I found one necessary.
I realize most aren't as hands on as a DIY'r

 

[fooferdoggie]

We will have to engineer a solution like that, and it can be done, but it would cost $500K to get this into production. Bosch has done an excellent job!

ya when you have the resources it helps.

 

[Gionnirocket]

From reading a few descriptions of devices for sale they do claim to parallel in use adding ah together for simultaneous discharge. That can definitely be a benefit reducing sag and keeping both batteries cooler under heavy use.

@6zfshdb... Why did you use a DPDT when a SPDT is all that is required as switching the negative wire does not serve a function other than total battery isolation if that for a reason is desired. But then it can also add a greater potential of short circuit with any type of failure and in wiring and mounting.
In all cases I hope it's a DC rated switch as an AC switch (which I've seen many times) does not provide enough contact spacing and arc protection. Especially concerning if switched under load.

 

[6zfshdb]

I use this one from Gardner Bender:

https://www.amazon.com/gp/product/B00004WLKA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The DC rating isn't specified but it's worked well for 2 years now. I have no reason to switch under full load and avoid doing so. To minimize the arc risk, the switch I chose has a center off position which allows for a complete momentary disconnect.

Yes, SPST would work but I use DPDT to totally isolate the batteries. There are several circuits on the bike which use ground return so I don't want to take chances.

 

[Gionnirocket]

I use this one from Gardner Bender:

https://www.amazon.com/gp/product/B00004WLKA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The DC rating isn't specified but it's worked well for 2 years now. I have no reason to switch under full load and avoid doing so. To minimize the arc risk, the switch I chose has a center off position which allows for a complete momentary disconnect.

Yes, SPST would work but I use DPDT to totally isolate the batteries. There are several circuits on the bike which use ground return so I don't want to take chances.

Yes that switch is not DC rated and that's what I've seen a lot of and why I thought I should mention it.
DC switches are large (typically ugly) and for a reason. If you do decide to use it, I'd be very conscious of only switching under no load.
I'd also consider isolating the negative as a failure could dead short both batteries at once.

 

[Bicyclista]

I know, @Ravi Kempaiah, that you asked for experience with high-voltage (52V) dual batteries powering hub-drive motors, so my experience is not directly relevant. I have been riding a mid-drive Yuba Spicy Curry AT with two batteries for the past 18 months. It is a Bosch system. A 36V system, if I remember correctly. The electronics automatically switch from one battery to another while riding, apparently doing so every 7 to 10% of usage. At the end of the ride the two batteries are similarly depleted, within 10% or so of each other.

I have not verified this, but while charging I believe the system similarly alternates charging one battery and then another, automatically. I use a timer to guesstimate charging both batteries to 80%. I usually end up with one battery at 75% and the other at 85%, more or less. Sometimes they are within 5% or less of each other.

Anyway, as others have pointed out, maybe discharging and charging one battery at a time is the safest operation.

 

[34Ford]

I am looking to buy a combiner and I have looked at 3 possibilities but none of the ones on amazon. Just curious if anyone has suggestions or which ones to stay away from. Thanks.

EDIT: I just watched a video that the best solution to two batteries is to just stop, unplug the primary battery and then plug in the secondary. Only take 30 seconds and is safer.

 

[teskow]

When switching (breaking electrical contact) with DC verses AC there can be much more of an arc with DC, such as a welder makes so the switches are designed differently.

 

[6zfshdb]

If you're talking about these battery balancers, I don't recommend using them.

Amazon.com

I had one overheat and almost catch fire. I now use a switch to change batteries.

Our resident battery expert @Ravi Kempaiah, posted this on the subject:

Dual Battery Balancer circuit - experiences!

Public Safety Announcement (PSA): The dual battery function is a favorite among many riders, and being able to connect 2 batteries and extend the range is an excellent feature. This is one of my favorites too. Bosch has implemented this in an excellent manner, and it works very well. But, I...

forums.electricbikereview.com

 

[Gionnirocket]

Be_careful people.
This needs to be done correctly and with the proper and I'll repeat quality hardware as failure is not an option.
And there's a very good reason that DC switches are large, have arc shields and only switch the positive wire.
Please don't think if it works = it works.
As it may on day one... and it may on day 365...but when you least expect it ...

 

[JedidiahStolzfus]

If the PCB inside that box is conformal coated be aware, that the coating is highly flammable even after it's set and will continue to burn after voltage is removed. Conformal Coating is used to keep moisture away from the circuits, but if something overheats on the board it quickly catches fire and spreads. It's also very difficult to rework a board that's been coated.

 

[6zfshdb]

Be_careful people.
This needs to be done correctly and with the proper and I'll repeat quality hardware as failure is not an option.
And there's a very good reason that DC switches are large, have arc shields and only switch the positive wire.
Please don't think if it works = it works.
As it may on day one... and it may on day 365...but when you least expect it ...View attachment 170678

The trick is to never switch under load. In my case, I located the switch where I can't reach it while riding.

 

[Gionnirocket]

The trick is to never switch under load. In my case, I located the switch where I can't reach it while riding.

Nice precaution.
Placing it where it can't be damaged is another.

 

[PCeBiker]

If the PCB inside that box is conformal coated be aware, that the coating is highly flammable even after it's set and will continue to burn after voltage is removed. Conformal Coating is used to keep moisture away from the circuits, but if something overheats on the board it quickly catches fire and spreads. It's also very difficult to rework a board that's been coated.

Thanks for that tidbit.

I was planning on coating the circuit board in my controller of my new e-bike.
I have now changed my mind.