Battery splitter box advice

VinDonaldson

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Hey guys. I have seen these battery parallel boxes at most ebike shops around here.

They claim to be able to run batteries in parallel with differing capacities. You can also set it up to auto switch to a different battery when one runs flat instead of parallel.

How does a splitter even out the difference in capacity and cells with a parallel setup?

Are these legit? I have a 36v 630wh narrow silverfish battery, and recently purchased a 720wh 36v pack for the top tube and would love to be able to run them in parallel. But I wouldn't normally trust two packs with different capacities and different cells to pair well in parallel.

I'm getting about 90-110km range running throttle at max off the 630wh battery on rough rail trails. It would be good to have two batteries in parallel to limit the voltage drop as well as get better range. Should get over 200km easy.
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Had a mate run two different capacity batteries on his scooter and one kept trying to charge the other and the BMS would shut down and go into charge mode as soon as the batteries were unbalanced. Would this just run like a second BMS which balances both cells?
 
1. There are "Split Decisions" on Combiner's/Blenders on this forum .

2. Originally this type of device had way over-stated claims - examples batteries could be combined that had different voltages (NOT so).

3. There are respectable Builders and enthusiasts here that have used them successfully "combining" 2 or more batteries of the SAME voltage.

4. Your combined capacity "blended" offers up to 15%-20% greater total range that "switching" between batteries - think of blended as resulting in a bigger single pool - over the capacity of 2 separate smaller ponds.

5. Here in the US - what appears to be the same model is offered "about" USD$50

6. Adding a 2nd battery and installing a combiner does take basic DC cicuit experience - eBike batteries have a ton of current that can dump real fast when connected improperly - that's one of the causes of eBike battery fires in New York City.
 
Let me count for you the number of consumer-grade, commercially available battery powered products sold anywhere in the civilized world where product liability laws are present, which allow for the parallel use of li-ion batteries.

ZERO. ZILCH. ZIP. NADA.

Your mate found just ONE, of the LEAST DANGEROUS, problems with such devices.

If you know enough to parallel two batteries, you know enough to do it without one of these cheap crap "magic boxes" which is very likely nothing more than a "Y" cable and a diode, and, more likely, you know enough to NOT DO IT in virtually ALL situations.
 
Pretty much what I expected. It's not exactly that much of an effort for me to pull over, power off and change a single connector, or make a Basic isolation switch.
 
I understand the Australian urge to be Frugal - but before you make a decision here - there has been some inaccurate info here.

1. I would NEVER advise anyone to directly parallel (2) or more eBike batteries - that's INSANE !
To "safely" do that both batteries at time of Parallel Connect would need to be within .1 (1-10th) of a volt between them or a "current dump" will occur from the stronger/V to the weaker /V

2. A "correct" isolation switch would allow you "safely" switch from one battery to the next - again your total mileage will be about 15%-20% less than you will get by "combining"

3. There are "Diode Combiners" - then there are "Chip Controlled Relay Combiners" (CCRC) - the eBike combiner you pictured (and that I have discussed here) I believe is of the CCRC category.
 
Speaking of inaccurate:
1. I would NEVER advise anyone to directly parallel (2) or more eBike batteries - that's INSANE !
No it isn't. It introduces risks, but they are manageable if you understand all of them, and therein lies the rub.
To "safely" do that both batteries at time of Parallel Connect would need to be within .1 (1-10th) of a volt between them or a "current dump" will occur from the stronger/V to the weaker /V
Which is super easy to do. The current dump happens for any differential. Just plug a new pack that has a low charge level into a lab power supply that lets you dial voltage. Charge it up a hair so your two new packs are the same. Should only take a couple of minutes each. Connect them. Job done. No drama.

I've said here repeatedly that directly connecting batteries in parallel is not something anyone should do unless they know how to do it safely. But misrepresenting the process to scare people off - and recommending a black box to take the place of a brain fully engaged in the process - is not the answer.

WTF is it with all of these idiotic magic blender threads lately? I guess they're just becoming more visible in the market. They've been around for years and by and large have not caused much of a stir.
 
I didn't intend to make an "idiotic thread". I just noticed these everywhere all of a sudden, but haven't actually seen anyone use them. Just wanted to cut through all the conjecture and get some differing opinions from people that might have used one.

Just thought it was interesting this exact model has shown up at pretty much all the local shops within a few months.

As far as I know these exact boxes originated on AliExpress years ago (that was the first time I saw them anyway). I've ran numerous scooters with dual batteries and isolation switches and have a few here I can add to the controller box which was intended plan for the bike but just wanted to know if they introduced any risks i wasn't aware of.

The general consensus is that I'm bats**t crazy, but I've used y cables plenty before for RC vehicles and scooters with no issues as well. I've just drained both packs until they read 33v and connected them without much thought, however both batteries always had identical cells, voltage and capacity.
 
Identical cells, Identical voltage, and Identical capacity. NOT ONE ad I have seen even suggests this as a good idea.

Somebody is making a buck on this crap, and a whole bunch of somebodies are lining up to get their asses sued clean off.

I will repeat this, if I was in charge of this site, I would BAN all mention of such products. You might as well advocate selling real firecrackers to grade school children.
 
Identical cells, Identical voltage, and Identical capacity. NOT ONE ad I have seen even suggests this as a good idea.

Somebody is making a buck on this crap, and a whole bunch of somebodies are lining up to get their asses sued clean off.

I will repeat this, if I was in charge of this site, I would BAN all mention of such products. You might as well advocate selling real firecrackers to grade school children.
I haven't advocated for anything in particular. You are just projecting at the moment. I asked a simple question.

Ive never seen anything offer a parallel setup at differing capacities and thought I'd converse about that option.

I didn't tell anyone to buy anything and I shouldn't have my posts banned or censored for merely asking a question about the legitimacy of a product.

Lighten up bud.
 
Is english your primary language?

I never stated YOU advocated for this crap, I DID say MANY are pimping this shiite.

They are dangerous, ESPECIALLY for the largely ignorant crowd that keeps asking for them.

Free speech is great, but should we have a nice long discussion about the best methods for putting firecrackers in the hands of elementary school children, or should maybe somebody with active brain cells shut that crap right down?

They are selling because they make a buck on the deal, and the pimps are pimping because they get paid as well.

Wonder how much money I could make teaching people to make a good napalm substitute with easily available household items?
 
I say this "eBikes build Character"- " every eBike owner I have met is certainly a Unique Character" .

1. Some "eBike Enthusiasts" that have DC background "might have" a Multi-Meter with scale to read 1-10th Voltacross a range of 48-52-60-72 Volt battery packs (I do have several in both Analog and in Digital) - and "some" enthusiast might have a "adjustable DC lab power supply" that across the choice of 48-52-60-72 volt range (yep, I have two digitals - and a straught adjustable DC power supply that I can adjust and set with one of my multi-meters.

2. Frankly - "most" eBike Enthusiasts DON'T have DC experience. Boat owners have larger DC system experienced - RC/Drone guys have smaller system experience... oh, and Christmas lights are DC too.

3. If you have ever experienced a eBike-Battery-Current-Dump knows that situation can literally turn a eBike battery into Fireball Bomb - it's scary because its happens so fast !

4. That's why I will NEVER RECOMMEND ebike batteries put into Parallel without a legitimate Combiner/Blender.

5. My 1st "Combiner" was 2yrs ago where I installed on my dual battery Ariel Grizzly - and THAT's where I measured 15%-20% greater distance with a Combiner over standard switching between batteries.

6. In the eBike segment - remember the vast Majority of owners are those who just want to get on the bike and do their thing - eBike "Enthusiasts" look to adjust and mod - and frankly in the eBike segment each enthusiasts is his (or hers) own character
 
Is english your primary language?

I never stated YOU advocated for this crap, I DID say MANY are pimping this shiite.

They are dangerous, ESPECIALLY for the largely ignorant crowd that keeps asking for them.

Free speech is great, but should we have a nice long discussion about the best methods for putting firecrackers in the hands of elementary school children, or should maybe somebody with active brain cells shut that crap right down?

They are selling because they make a buck on the deal, and the pimps are pimping because they get paid as well.

Wonder how much money I could make teaching people to make a good napalm substitute with easily available household items?
I was assuming you were accusing me of advocating for them based on how quickly you came in a bit heated but that assumption was obviously a bit rash, and I mistook the obvious passion for aggression.

I've never seen anyone advocate for them, and have never heard or seen anyone actually using them so I was unaware there was a lot of talk about these in general.

I was all good until I read "different capacities" and thought I might just converse in general.
 
I say this "eBikes build Character"- " every eBike owner I have met is certainly a Unique Character" .

1. Some "eBike Enthusiasts" that have DC background "might have" a Multi-Meter with scale to read 1-10th Voltacross a range of 48-52-60-72 Volt battery packs (I do have several in both Analog and in Digital) - and "some" enthusiast might have a "adjustable DC lab power supply" that across the choice of 48-52-60-72 volt range (yep, I have two digitals - and a straught adjustable DC power supply that I can adjust and set with one of my multi-meters.

2. Frankly - "most" eBike Enthusiasts DON'T have DC experience. Boat owners have larger DC system experienced - RC/Drone guys have smaller system experience... oh, and Christmas lights are DC too.

3. If you have ever experienced a eBike-Battery-Current-Dump knows that situation can literally turn a eBike battery into Fireball Bomb - it's scary because its happens so fast !

4. That's why I will NEVER RECOMMEND ebike batteries put into Parallel without a legitimate Combiner/Blender.

5. My 1st "Combiner" was 2yrs ago where I installed on my dual battery Ariel Grizzly - and THAT's where I measured 15%-20% greater distance with a Combiner over standard switching between batteries.

6. In the eBike segment - remember the vast Majority of owners are those who just want to get on the bike and do their thing - eBike "Enthusiasts" look to adjust and mod - and frankly in the eBike segment each enthusiasts is his (or hers) own character
At the end of the day the 720wh secondary battery is enough of a help that it's not exactly necessary I run them in parallel anyway. Was just interested when I saw "different capacities" and "parallel" and thought I'd just converse in general.

At that stage I wasn't even looking to run the battery in parallel or use that combiner as I only plan on using the secondary battery a month when i ride the rail trail. Funny thing is that there is unassisted riders doing the same 200km trail anyway over a day or two, so I should feel blessed to have assist full stop.

I've dealt with basic 12 and 24v systems off grid and assembled a bunch of parallel systems made out of tested an recovered laptop cells, have a bit of experience with RC and drone systems alongside a few years finding and fixing shorts and mosfet/capacitor burnouts on motherboards (especially VRMs), but wouldn't call myself well versed.

I am lucky enough so far to have never had any issues or current dumps and hope it stays that way.
 
Identical cells, Identical voltage, and Identical capacity.
Add to that identical charge cycles and ideally the builder has gone thru a batch of cells individually and matched the ones that fully charge to levels as close to one another as possible.

I didn't intend to make an "idiotic thread". I just noticed these everywhere all of a sudden, but haven't actually seen anyone use them. Just wanted to cut through all the conjecture and get some differing opinions from people that might have used one.
I didn't mean to imply idiocy on your part. Its just frustrating to see something like this pop up all over the place all of a sudden and make a very fringe topic one that needs to be addressed over and over again - and I say that as being someone who is active on a lot of fora so I am not just crying about what I see here on this one.

To repeat an important point I've said elsewhere but not here: These devices are completely unknowable in terms of whether or not they use quality manufacturing techniques or even if they are fit for the stated purpose. Thats what I mean when I call them 'black boxes'. Safety becomes a big what-if that you can't answer. I'd say its a bit different if you are using the one or two brands that have been in the market for years. But sure as hell nothing from AliExpress.
 
I have 2 of these on the first pair of 48v e-bikes I purchased. They seem to work fine. These bikes only pull 18amps. Not sure how efficient they are. Since then I have not used them. I run parallel wired direct but the batteries have to be the identical voltage or else the voltage transfer will be at high amperage and hurt battery. AH capacity can differ, cell type can differ, just the voltage needs to be the same.
I simultaneously charge both batteries installed on the bike. This guarantees the same voltage in each pack. No issues, been doing this for quite a while.
Usually my 2nd battery is one I build. I don’t use a BMS, just active balance board and fused.
 
Summary: What do some of the magic boxes do?

1. They keep current from flowing from the battery with a higher voltage, into the battery with lower voltage (back-feeding). Back-feeding is quite bad and can damage the battery. This is where a "battery combiner" earns its keep.

2. Eventually, because the "more charged battery" is doing most the work, its voltage lowers to the level of the less charged battery.

3. At this point, the two batteries are working together to provide power for the "load" (Electronic Speed Control (ESC) powering the brushless motors).

4. Once equalized, (and ignoring the potential difference in the Impedance (internal resistance) of the batteries, the two batteries are equally providing power to the Ebike. If your two batteries are "matched" the internal impedance should be very similar.

5. The most ideal circumstances are two batteries of the same voltage, brand/type, amp-hour figure, and same Max Current deliverable by the "battery management system".

6. Most batteries have a "low voltage cut-out", which keeps them from being drained below safe levels. Once one battery has hit the low voltage cut-out, then only one battery will be carrying the load. If this is the case, the remaining battery is also close to the low voltage cut-out.

Other factors: Heavy current drawn from a single battery will "sag" the available voltage it can deliver. It makes it more likely that battery will hit its low voltage cut-out. When two batteries are working together (and sharing the load), you get LESS SAG in the voltage. This allows the two batteries working together to avoid the low voltage cut-out more effectively. This is why two batteries "combined" can get you more MILES travelled, than the same two batteries running one after the other.

Some are very simple and use a Schottky barrier diode which is known for having a minimal loss of voltage across it. But, it only allows current to flow to the load, and not to the other battery. Others use Power MOSFET transistors to "switch" power to the load. Both typically require a heatsink with airflow across it. Some makers of these products void the warranty if you overheat them.

Some of these modules support two batteries at once. Others can support up to four batteries at once.

I was an engineer for a physics lab, and we had field instruments which required power for weeks/months. I would design a circuit to handle multiple batteries powering the instrumentation packages (sometimes mixed types (Lithium, Lead Acid, Edison Air-Cell). This is Decades before Ebikes even existed. They work well, if properly designed. They eliminate the problem of back-feeding power to the dead batteries, when you added a hot-fresh battery. I even used them with wind/solar combined power sources to charge batteries. As long as the wind was blowing OR the Sun was shining (or both), the batteries were getting charged at the best rate.

And yes, in a week or so, one of these kinds of products will be on my Ebike. I am certainly willing to put my money where my mouth is. If I don't like the commercial product, I will engineer my own.

Anyone who has been an engineer for over 40 years, is free to "try" to dispute me.
 
Well this will be my setup for 2 batteries.

I will run a splinter from my controller to my 2nd battery. OK, this is how I use it.

When my main battery is getting low, Then I will turn off my main battery then I will turn on my 2nd battery and I will be back in business!
I do not want to run both batteries and the same time cuz the batteries will be different. My main battery is a 48v 24amp. My 2nd battery will be 48v and 40amps. That is why I will not have both batteries on at the same time because of balance issues.

Hope that helps ;)
 
Summary: What do some of the magic boxes do?

<snip>

Anyone who has been an engineer for over 40 years, is free to "try" to dispute me.

The issue is not the claimed feature set. You could have saved yourself a lot of typing. The issue is quality and reliability of the manufacturer and the materials they used. You are betting your house and your ass on an AliBaba advert.

Also most of your post talks about the generic properties of parallel'd batteries. All of those things are true (and important to know) but have nothing to do with the optional black box of unknown quality stuck in between.
 
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