Determining how to charge Bosch smart battery off solar/another option.

[robotron2084]

Hello, me and my wife are doing some e-bike touring and I'm looking at ways to get her bike charged while touring. My bike is set up for solar and it charges and runs great. But I built up my bike and it 'runs' off solar pretty well. As some may know, solar takes a while to charge, but this is something we are patient with.

So current setup:
2 100w flexible solar panels -> sunforge charge controller -> watt meter -> battery. Battery connects via xt60 to motor.

Her bike is a Tern GSD and has a Bosch Smart System with a 6-pin plug. She really likes this bike and we've already done some long trips, but we're looking to go more remote, meaning we'd like to utilize the existing gear and connect it to her bike. We're thinking we will buy a 2nd battery. This will allow her to achieve the mileage we're looking for. This also allows for things like charging one battery while using another. Then:

Option A: On my bike, I can connect via xt60 a ~300W inverter and plug in the Bosch charger to charge her battery off mine. I can simultaneously connect the solar to my battery, meaning that some of this would pass through. I already have a step-down converter to provide 12v that I can connect via a splitter cable, so this would basically involve getting an inverter, and carrying her charger. Pro: this seems pretty straightforward, but the inefficiencies here are pretty big. I don't know how big but the cost of converting from 48v->12v->120vAC->36v seems like a huge waste. Not sure if I'm over-optimizing here, but this just feels like a lot of steps.

BESTEK 300Watt Pure Sine Wave Power Inverter with PD 30W USB-C QC18W USB Ports DC 12V to AC 110V

www.bestekdirect.com

Option B: Somehow, and really I'm not sure how, figure out a 'dc-only' path that is compatible with Bosch's system. Someone figured out with the Bosch system how to charge from dc using the older 3-pin system with a big buck-boost converter and a smaller 5v buck. Apparently the 5v buck is required because the battery will only charge if 5v is sensed on a pin. Someone also mentions a 7805 voltage regulator can function as a replacement for the 5v buck, which makes sense, but a bit farther outside of my expertise.

Related video:

So the thing that's blocking me here is that I've got a 6-pin setup and I can't seem to get any info on this online. I'm not entirely sure how to probe the pins to figure out how feasible this is to replicate. Also when I've got that info, I either have to a) draft up the part and 3d print it or b)buy a bosch adapter and cannibalize it for the plug. Then I'd have to get, say, a charge controller that operates at 36v, and possibly provide 5v to a pin (or two?) to do the charge.

Does anyone have any info on this 6-pin connector from Bosch? Is it feasible to charge this bosch battery using something like Option B? Or how can I test the pins to get this information without anything bursting in flames?

Thanks!

 

[robotron2084]

 

[amberwolf]

Her bike is a Tern GSD and has a Bosch Smart System with a 6-pin plug.

The 6-pin plug is the input to the battery from the charger?

If so, presumably there is some form of communication or signaling between them?

Option A: On my bike, I can connect via xt60 a ~300W inverter and plug in the Bosch charger to charge her battery off mine. I can simultaneously connect the solar to my battery, meaning that some of this would pass through. I already have a step-down converter to provide 12v that I can connect via a splitter cable, so this would basically involve getting an inverter, and carrying her charger. Pro: this seems pretty straightforward, but the inefficiencies here are pretty big. I don't know how big but the cost of converting from 48v->12v->120vAC->36v seems like a huge waste. Not sure if I'm over-optimizing here, but this just feels like a lot of steps.

It is a lot of steps. At a guess you probably lose about a quarter of the power involved at each step. (couild be less, or more)

There are inverters that run directly from 48v to provide the AC, which would eliminate one step.

If the BSS doesn't use comms between charger and battery, or they are simple to replicate (a voltage pullup or pulldown, resistor combo, etc), then the most effiicnet way is a simple current-limiting DC-DC stepdown between the 48v and the 36v battery. IIRC there are MPPTs (or other solar stuff) that can do this.

Option B: Somehow, and really I'm not sure how, figure out a 'dc-only' path that is compatible with Bosch's system. Someone figured out with the Bosch system how to charge from dc using the older 3-pin system with a big buck-boost converter and a smaller 5v buck. Apparently the 5v buck is required because the battery will only charge if 5v is sensed on a pin. Someone also mentions a 7805 voltage regulator can function as a replacement for the 5v buck, which makes sense, but a bit farther outside of my expertise.

The 7805 is a very simple 3-pin regulator that just needs ground and power input from the source, and the same ground out to the destination plus the power output. Needs a big heatsink (probably with a fan) to ditch the waste heat from this big a stepdown...and the 7805 can't directly handle the input voltage available here, so you'd have to do something like this

https://forum.allaboutcircuits.com/threads/high-volt-options-for-7805-voltage-regulator.66868/

to use one in this situation.

A switching DC-DC buck would probably be more efficient and smaller (and probably woudlnt' require a big heatsink/fan given the teeny tiny load).

The question is, then, whether the 6-pin BSS uses a similar simple signaling system, or a more complex one.

So the thing that's blocking me here is that I've got a 6-pin setup and I can't seem to get any info on this online. I'm not entirely sure how to probe the pins to figure out how feasible this is to replicate.

Ideally you would open up the charger and the battery to access the pins and measure them with an oscilloscope before connection, then during connnection, then during charge and then when charge is complete, in case any of them is used to control the process.

Practically, you could check each connector end before connection using a voltmeter, everything referenced to the battery negative (black meter lead goes there) on each connector. To measure during / while connected, you'd have to open charger or battery up or cut into the cable to access the wires, unless the connector itself is disassemblable.

As long as there's no actual communication, the latter will show you what's needed, but if there's comms you can't see them this way (you might see that there's a 2.5v signal instead of 5v, if it's switching on and off rapidly); you'd need an oscilloscope or signal analyer for that...but at that point it might get more complex than you'd want to / be able to work around.

 

[amberwolf]

There've been a number of posts about these systems in general here on ES, but none appear to have the required info.

I don't know which Bosch battery these people used, but they apparently found a solution to charging theirs for their tour

ebikecycletourists

endless-sphere.com

though they never posted here what it was (despite three separate threads about it, two of them where people tried to help them figure one out).

 

[amberwolf]

Side note: This post warns that some of the batteries are designed to prevent reassembly if opened

Turn on Bosch Powerpack 500 for accessory usage

Been given a pair of these, don't have much use for them other than powering the 12v system in my garage as I already do with my old 48v bike battery connected to a 24-72V-12V driver. Issue is they don't just provide power automatically, there's extra pins on the pack I assume are to tell the...

endless-sphere.com

 

[amberwolf]

This person repairs some of the bosch batteries

Batteryrepair

endless-sphere.com

and might have some info on the issues involved.

 

[robotron2084]

The 6-pin plug is the input to the battery from the charger?

If so, presumably there is some form of communication or signaling between them?

Correct. The plug shown goes into the bike, which then connects to the battery internally. Its possible to plug that directly into the battery, although I haven't really done that.

It is a lot of steps. At a guess you probably lose about a quarter of the power involved at each step. (couild be less, or more)

There are inverters that run directly from 48v to provide the AC, which would eliminate one step.

If the BSS doesn't use comms between charger and battery, or they are simple to replicate (a voltage pullup or pulldown, resistor combo, etc), then the most effiicnet way is a simple current-limiting DC-DC stepdown between the 48v and the 36v battery. IIRC there are MPPTs (or other solar stuff) that can do this.

The 48v inverters I've seen are huge, usually for RVs or homes or something, which would probably be really inefficient and also quite heavy.

The 7805 is a very simple 3-pin regulator that just needs ground and power input from the source, and the same ground out to the destination plus the power output. Needs a big heatsink (probably with a fan) to ditch the waste heat from this big a stepdown...and the 7805 can't directly handle the input voltage available here, so you'd have to do something like this

https://forum.allaboutcircuits.com/threads/high-volt-options-for-7805-voltage-regulator.66868/

to use one in this situation.

A switching DC-DC buck would probably be more efficient and smaller (and probably woudlnt' require a big heatsink/fan given the teeny tiny load).

Yeah, maybe a switching buck is the way to go here, good point! I will probably do that first if I end up going this direction.

The question is, then, whether the 6-pin BSS uses a similar simple signaling system, or a more complex one.

Pretty much this!

Ideally you would open up the charger and the battery to access the pins and measure them with an oscilloscope before connection, then during connnection, then during charge and then when charge is complete, in case any of them is used to control the process.

If only I owned an oscilloscope!

Practically, you could check each connector end before connection using a voltmeter, everything referenced to the battery negative (black meter lead goes there) on each connector. To measure during / while connected, you'd have to open charger or battery up or cut into the cable to access the wires, unless the connector itself is disassemblable.

As long as there's no actual communication, the latter will show you what's needed, but if there's comms you can't see them this way (you might see that there's a 2.5v signal instead of 5v, if it's switching on and off rapidly); you'd need an oscilloscope or signal analyer for that...but at that point it might get more complex than you'd want to / be able to work around.

So there's kind of a 'simple' route, where basically the 6-pin version might work like the 3-pin, and the hope would be that a simple voltage sensing is required at the most to trigger charging. Or there's the complex route where Bosch has basically DRM'ed the battery charging and its an involved process.

I had an interesting thought where I could open up the bosch charger and look for a place that looked like it would make sense to solder a couple wires in, and attach an xt60 to it. The idea being that there's possibly a spot between the rectifier and capacitors (or something) at which I could read 36v then just plug it in right there. I would still need to figure out how to provide 36v from the panels. So if I can provide a steady 36v in, the charger I already own could do the rest.

Thanks for the replies and additional info. Still looking through it all. Its interesting to see that those tourists did a world record with their bosch setup. The systems are really nice, I just wish it wasn't so locked down.

 

[amberwolf]

The 48v inverters I've seen are huge, usually for RVs or homes or something, which would probably be really inefficient and also quite heavy.

Just googling "48v inverters" has this as the first hit

48 Volt Pure Sine Wave Power Inverter | Inverters R Us

Check out our great selection of 48 Volt Pure Sine Wave Power Inverters. We provide the most power at the best price, guaranteed!

invertersrus.com

I don't know anything about the site or the specific inverters, but they don't seem all that big to me. The 250w version is 3.4" x 6.5" x 10.2", 5.3lbs. 500w version is less than twice that weight and barely bigger. Chart for the first one on the page, the Victron (a brand I have used various DC-DC's from over the years, without problems).

If only I owned an oscilloscope!

If you have an android phone, there are assorted scope attachments out there; I don't know details about any of them, but I've seen them when looking for something easier to use / carry around than my old Hitachi V209 "portable" (it's battery hasn't ever worked while I've had it).

Some of them are logic analyzers, which are probalby more useful for this sort of thing; they usually use a USB connection to the phone. Some of the cheapest scope apps just use the mic input jack of the phone as the signal source, so it is limited to the frequency range of that jack's internal amplifier, and of whatever other limitations the phone's OS/etc places on it. They're useful for certain things, and might be ok for this, but you're usually limited to a single channel, and you might need two to properly reverse engineer serial coms if there is a TX and RX line. If it's a single wire serial (of which there are several protocols) one-channel scopes still work.


If it's CANBUS then it's both simpler and harder--you would already know the protocol, but all the data on the bus is probably proprietary and you'd have to figure it out (but this has been done for various things here on ES and elsewhere).

If it's totally proprietary you'd have to figure out everything.

BUT: It might be as simple as recording the signal that starts the charging process, and the signal the charger responds with (if any), and play the one back in response to the other, using something like a Pico or Nano.

So there's kind of a 'simple' route, where basically the 6-pin version might work like the 3-pin, and the hope would be that a simple voltage sensing is required at the most to trigger charging. Or there's the complex route where Bosch has basically DRM'ed the battery charging and its an involved process.

Unfortunately the latter is pretty likely. It prevents a user from ever using the wrong charger and potentially causing a fire or damaging the battery in a way that could cause one later, so it can at least make them feel less liability for users' mistakes.

It also makes it harder for bike thieves to sell the thing if they didn't steal the charger, too, at least for buyers that are smart enough to know they'll need a charger (as we've seen here with the occasional unlucky used-bike buyer, that's not always true).

I had an interesting thought where I could open up the bosch charger and look for a place that looked like it would make sense to solder a couple wires in, and attach an xt60 to it. The idea being that there's possibly a spot between the rectifier and capacitors (or something) at which I could read 36v then just plug it in right there. I would still need to figure out how to provide 36v from the panels. So if I can provide a steady 36v in, the charger I already own could do the rest.

I don't think the real issue is with the charger. I think it's with the battery BMS--it almost certainly won't accept a charge except from something that provides the right response, (be that a voltage or a comm signal).

You could bypass the BMS's charge FETs or other control element (if it has any) and go directly to the cells, but the BMS cannot then stop the charger if any cell reaches HVC, and that has the potential to damage cells. Won't happen unless the cells are mismatched or unbalanced.

 

[robotron2084]

Just googling "48v inverters" has this as the first hit

Well, I guess I failed at googling this time.

I don't know anything about the site or the specific inverters, but they don't seem all that big to me. The 250w version is 3.4" x 6.5" x 10.2", 5.3lbs. 500w version is less than twice that weight and barely bigger. Chart for the first one on the page, the Victron (a brand I have used various DC-DC's from over the years, without problems).

Thanks for the link! I had no idea that Victron made these. I've pulled the trigger on that Victron and I've heard good things before about them from elsewhere. I went for the one that's 260w continuous, which gives a good ceiling. I'm not super excited about bringing a 6lb inverter around but this is by far the easiest setup for the Bosch. If its really 90% efficient then that's not a huge cost.

Unfortunately the latter is pretty likely. It prevents a user from ever using the wrong charger and potentially causing a fire or damaging the battery in a way that could cause one later, so it can at least make them feel less liability for users' mistakes.

It also makes it harder for bike thieves to sell the thing if they didn't steal the charger, too, at least for buyers that are smart enough to know they'll need a charger (as we've seen here with the occasional unlucky used-bike buyer, that's not always true).

Yeah, I think while the engineer in me would like to understand what's going on under the hood, and I think this would be valuable to the community, I also don't want 'yet another project'. So I think if I can get away with the inefficiencies with this inverter and we're only adding a few pounds to the setup, hopefully I don't need to learn how to debug a canbus

 

[amberwolf]

Well, I guess I failed at googling this time.

If it helps: If you are logged in while googling, you will get different results than someone else will, since it shows you more of what you have already seen (which is pretty retarded for a search engine when you're actually trying to find things, rather than just confirming something you want to be right :lol: ).

If instead you do googling in an incognito window without logging in, you will get "generic" results that should be the same as anyone elses doing the same thing. those results can be more useful for many searches, though if you have specific preferences in things a logged in search may find more relevant things.

Other search engines may work differently, but I primarily use google as I can usually force it to give me the results I am after.

Thanks for the link! I had no idea that Victron made these. I've pulled the trigger on that Victron and I've heard good things before about them from elsewhere. I went for the one that's 260w continuous, which gives a good ceiling. I'm not super excited about bringing a 6lb inverter around but this is by far the easiest setup for the Bosch. If its really 90% efficient then that's not a huge cost.

At least it's one step out of the chain of losses.

And one less thing to fail and leave you unable to charge...

Yeah, I think while the engineer in me would like to understand what's going on under the hood, and I think this would be valuable to the community, I also don't want 'yet another project'. So I think if I can get away with the inefficiencies with this inverter and we're only adding a few pounds to the setup, hopefully I don't need to learn how to debug a canbus

Yeah. I know how it is. I have a bajillion ideas and projects I want / need to do, most of which I can't even start (time, money, whatever), but even the few dozen things I have going are....well, projects.

My biggest project: All I want is a fairly realistic snuggle wolfy that can "behave" like one, cutely, in response to user input. (that I can then publish as open source so anyone who needs this kind of emotional support can make it or have it made for them). But I have had to learn (still working on that) robotics, mechanical stuff, sewing, leatherworking, fur (fake and real) dyeing, moldmaking and casting, coding, AI, etc. I still doubt that I yet know even half of what I need, far less than that on the coding stuff, and I've been working on this for decades so far....I might finish it in time to be snuggled up with it in my coffin. :/ :lol:

 

[robotron2084]

My biggest project: All I want is a fairly realistic snuggle wolfy that can "behave" like one, cutely, in response to user input. (that I can then publish as open source so anyone who needs this kind of emotional support can make it or have it made for them).

Is this a bit of a robotic support animal. Ngl that is a pretty weird sounding project!

So the inverter arrived yesterday. Today I made a cable with an xt60 connection for it and connected it to my bike. I ran a fan as a light test and it worked as expected. I also purchased the bluetooth dongle on a whim, and it really was worthwhile, as it allowed me to update the firmware and watch the inverter in realtime. Here's a pic of the 'source bike' with the inverter connected and the Bosch charger plugged in to the inverter.



Here's the info from the inverter with it plugged in. I picked the 375VA model, which does 260W constant current, and it looks like, with the charger plugged in, I sized it right for the power. The 300W inverter from Bestek I linked to above is *way* smaller and thinking about it, I'm not sure that it will provide a constant 200W of power.

And here's the screenshot from my battery, showing that its pulling 3.75A, ~200W.


The Bosch charger is a 4A 36V charger. So to do the math here:

36V * 4A = 144W
197W - 144W = 53W
53 / 144W = 0.3688 = 36.8% wasted energy

Pros:
-dead simple, quality inverter. Well sized for the task.
- I can kind of charge two batteries at the same time! Once the bosch is charged, then the other battery charges.
- Maybe having an inverter available to plug stuff in will be handy? I can plug a lot of things in here.
- Allows for a 100% solar setup for both bikes. This the main goal, and it gets it done.

Cons:
- Heavy and bulky. Its about the size and weight of a battery. For shorter trips, its likely better to just figure out places to charge or carry another battery.
- Inefficient: All of this could be way easier and I could remove most of the 37% of this wasted energy if I could just charge the battery through a standard 36v charge controller.

In general I think the setup is pretty acceptable for us to experiment with. I'll be going on an overnight camping trip for a couple days, that is 40m away. We'll see what happens!

 

[amberwolf]

Is this a bit of a robotic support animal. Ngl that is a pretty weird sounding project!

Everything I do and think and make is wierd, so that's no surprise. The present nonrobotic prototype is my present avatar. Robotics Project: Snuggles, The Wolf
Even my music is wierd. Amberwolf
And you've probably seen my rides around the forum....


BTW, I just now realized where your username was familiar from...and while I liked that game, I had more fun with Defender. (a version of which can be played online in the stats page of bandcamp if you have an account there, if one is very very bored and can't sleep or concentrate on anything).

Here's the info from the inverter with it plugged in. I picked the 375VA model, which does 260W constant current, and it looks like, with the charger plugged in, I sized it right for the power. The 300W inverter from Bestek I linked to above is *way* smaller and thinking about it, I'm not sure that it will provide a constant 200W of power.

I don't know the brand, but there are certainly a lot of things out there that couldn't continuously provide their "rated" power without help (such as external cooling, etc). We see that very frequently in assorted troubleshooting threads around here.

I like that there's a way to see what's going on realtime. Is that the only data the Victron app can show?

The Bosch charger is a 4A 36V charger. So to do the math here:

36V * 4A = 144W
197W - 144W = 53W
53 / 144W = 0.3688 = 36.8% wasted energy

That's probably typical efficiency for chargers...which is why it would be nice to eliminate that stage and go direct to the battery, if you can find out how to tell the BMS to allow charge.

In general I think the setup is pretty acceptable for us to experiment with. I'll be going on an overnight camping trip for a couple days, that is 40m away. We'll see what happens!

Also--if you have a power outage at home, you can at least use the batteries to power smaller loads if you have to.