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[electrictwowheeler]

the ssd's have turn on points on them, many you can control when it activatres,  for DC that pretty much is eliminated, but a cheap controller, anything that can monitor voltage and put out a signal, arduino or raspberry would work, or even a simple monitor.  you could get fancy like a yokogawa or something of that nature but that's a lot of money and way too much for just this small purpose. 
you monitor the voltage difference between the packs with whatever you choose to monitor, and that in turn sends the signal to the ssr to turn on or off.
some ssr's have an a and b input and depending on the model, again, you have to do your own homework, will turn on, or off depending on what's on those inputs, or a difference between those inputs. *gee it's almost like they are made for this purpose huh*  you select the one for the job and plug it in. 
i don't know what parts you have or how you want to run it, if you want something else looking at the volts and send a signal to the ssr, that works and gives you more control, or if you want something less sophisticated, like the a-b input which turns the relay on if volts between the points is less than say 0.5. 
i know they make them, not sure how many amps they go up to, you'll have to get one that will fit your project. plug that in and it will only turn on if the batteries are within the set range of each other.  most have a pilot light on the ssr that will tell you if it's activated or not.

plan your rig carefully.
aaron

Thanks for the clarification! That gives me enough information to at least do some research. I'll do some testing with the pack in the bike and find out how much current is actually flowing between the packs under the max load which would be full acceleration in sport mode and try to measure the voltage difference between the two packs under the same condition. That would give me an idea of what hardware I would need.

[electrictwowheeler]

Diodes would not allow for regen. Current needs to flow back and forth between the packs when the bike is ridden. Diodes could protect if the extender was at a lower voltage than the main pack, but, what if the extender was at a higher voltage?

Ok, back to the drawing board……

First how big of a deal would that be if the extender didn’t receive charge during that brief period?
Because the extender is an order of magnitude (1/10) less of the main, it’s my thought that it will typically tend to react faster to levels of charge (mains mass acts as a buffer).
Therefore (if I’m right) it’s the extender that needs protection from the main & not the other way around. 
Second, if counterflow is required/desired during operation, segregate the paths (charge/discharge) with separate diodes with suitable sized fuses to handle an acceptable current for the 4@18650 2.5ah battery arrays. If the fuse size turns out to be the same value on both circuits, then it makes my suggestion of diodes superfluous. 
Maybe use a resettable circuit breaker instead of a onetime fuse???

How does Zero handle this protection on their power tank?

Well, regen is not always a brief time, going down a long steep hill and using regen to keep the speed down can in some instances go on continuously for some time. I was once at the top of the coast range here in Oregon  at 3000 feet and the road down was steep for 10 miles and I gained 3 % soc by the time I got to the bottom the bottom.
I think you are correct that the extender is what needs protection.
I am not sure how you could segregate the charge and discharge paths. The packs are just connected in parallel with a positive and negative wire. I don't see any way that diodes could solve the problem.
I considered a circuit breaker but chose a fuse because I wanted it to be as close to the positive connection as possible. it couldn't be connected directly to the buss bar because of space restrictions so it's down low behind the right-side fairing. Not easily accessed and it needs to be waterproof, but I could mount one on the pack itself. It could be of  the minimum capacity needed. It's a thought ! Thanks for your ideas!

[ESokoloff]

“ I am not sure how you could segregate the charge and discharge paths. The packs are just connected in parallel with a positive and negative wire. I don't see any way that diodes could solve the problem.”

The separate paths would be to add a second conductor on + or - side & install diodes on each conductor that block current in opposite direction.
This would only be required if it’s found that the extender battery cells have different charge/discharge amperage values.
If the same or close to the same, there’s no reason to do this.

Maybe ask on RC, or off grid forums or other electronics based sites how best to protect the batteries. 

[Specter]

the SSR's depending on how much power and for how long may want heat sinking, id recommend it, they sell them with sinks already installed, its a bit more money but well worth the hassle if you don't have a known place to put it where you know it'll fit etc etc.  you could use a regular relay too but i find that solid state behaves better over the long term, especially in high vibration places, no mechanical rattling around.

the input to turn on the ssr is typically very small, like a few ma, so even a pilot relay would work fine for the switch on them.  some controllers limit you on how much power you can route through them or use them to feed a 'turn on' to something. to like 250 ma max.  This is another reason i like ssr's as some relays, the coils can draw some really insane power at times and lets say it gets stuck, now you are pulling hard amps, which could damage your signal supply device. also,  while this may not be too important, watch the deadband too on the ssr,  generally they are small enough so it's not going to be an issue with turn on / off given the range we are working in.

you can go thru a grainger catalog or somewhere similar to get an idea of what kind of ssr's are out there and start narrowing down what you'd want to use, then either get it thru them if they let you or go somewhere where it's cheaper, as they tend to be very proud of their items sometimes 

while this may be a fun project, and give some nerd cred  it's really not something that is 'needed' if one just remembers to check the voltages tween the batteries before connecting them.  A good rule of thumb would be either to leave em connected, or install it when both are fully charged as an example, that way you know they both are at the proper volts.  im assuming the main reason youd want to put the extra tank on is because you are planning on making a longer trip, in which case you are going to charge it up all the way anyways.

if you are running both batteries, you don't want diodes and all that crap in the circuit really, you want them to both charge and discharge the same from use to include charging from  both normal charging and regen.  Remember the key is to keep their voltages even.,   As mentioned, regen can put significant power into the setup, and anything like diodes that you put in the main current path just add voltage drops, and losses to the overall power train, not to mention youd have to heat sink the diodes too, and thats even more clutter.

diodes are not going to help at all, and in fact would prevent you from charging the pack from any source, as the bus does not know where the power is coming from, whether it be a charger or regen.

aaron.

[electrictwowheeler]

the SSR's depending on how much power and for how long may want heat sinking, id recommend it, they sell them with sinks already installed, its a bit more money but well worth the hassle if you don't have a known place to put it where you know it'll fit etc etc.  you could use a regular relay too but i find that solid state behaves better over the long term, especially in high vibration places, no mechanical rattling around.

the input to turn on the ssr is typically very small, like a few ma, so even a pilot relay would work fine for the switch on them.  some controllers limit you on how much power you can route through them or use them to feed a 'turn on' to something. to like 250 ma max.  This is another reason i like ssr's as some relays, the coils can draw some really insane power at times and lets say it gets stuck, now you are pulling hard amps, which could damage your signal supply device. also,  while this may not be too important, watch the deadband too on the ssr,  generally they are small enough so it's not going to be an issue with turn on / off given the range we are working in.

you can go thru a grainger catalog or somewhere similar to get an idea of what kind of ssr's are out there and start narrowing down what you'd want to use, then either get it thru them if they let you or go somewhere where it's cheaper, as they tend to be very proud of their items sometimes 

while this may be a fun project, and give some nerd cred  it's really not something that is 'needed' if one just remembers to check the voltages tween the batteries before connecting them.  A good rule of thumb would be either to leave em connected, or install it when both are fully charged as an example, that way you know they both are at the proper volts.  im assuming the main reason youd want to put the extra tank on is because you are planning on making a longer trip, in which case you are going to charge it up all the way anyways.

if you are running both batteries, you don't want diodes and all that crap in the circuit really, you want them to both charge and discharge the same from use to include charging from  both normal charging and regen.  Remember the key is to keep their voltages even.,   As mentioned, regen can put significant power into the setup, and anything like diodes that you put in the main current path just add voltage drops, and losses to the overall power train, not to mention youd have to heat sink the diodes too, and thats even more clutter.

diodes are not going to help at all, and in fact would prevent you from charging the pack from any source, as the bus does not know where the power is coming from, whether it be a charger or regen.

aaron.

Thanks for all the information! It looks like a big project to me. Yes, I'm just looking for longer range. Sometimes I go places with sparce charging infrastructure and even 10 miles extra helps, and the more you leave with, the less charging on the way. I tested the inrush current with the packs at 4 volts difference, only 10 amps so the packs really only have to be close in voltage. Very easy to do. Once in there it will be fine, I think. It should work fine the way it is. Can't wait to do a long trip!

[Specter]

is there any way to just leave it on permanent, or would you not want to do that?  looking at age .vs. cycles etc, its best if you can keep everything about evenly aged / used.

oh i totally get the ..even 10 miles helps.  when i goto the track with my tesla, its like ok i drove a little fast going there, can i make it home w/o having to charge, do i need to slow down or turn the ac down to make it w/o having a recharge session. it always seems your trips end up at the extreme ends of a batteries charge for some reason !  then again if i am not towing or know ill have a charger available where i am going ill run bitcoin miners in the thing while im driving.  helps heat in the winter hehe.

aaron

[electrictwowheeler]

is there any way to just leave it on permanent, or would you not want to do that?  looking at age .vs. cycles etc, its best if you can keep everything about evenly aged / used.

oh i totally get the ..even 10 miles helps.  when i goto the track with my tesla, its like ok i drove a little fast going there, can i make it home w/o having to charge, do i need to slow down or turn the ac down to make it w/o having a recharge session. it always seems your trips end up at the extreme ends of a batteries charge for some reason !  then again if i am not towing or know ill have a charger available where i am going ill run bitcoin miners in the thing while im driving.  helps heat in the winter hehe.

aaron

I will only use it for longer trips because it ads weight up high and takes up the handy storage space. The cells in the extender are old but have not been used very much and I'm sure they have more resistance but that doesn't seem to have any ill effect. They test to 2500mah each which is the nominal capacity when new. I did a 100 mile ride with the extender installed, mostly rural highways but some freeway and the extender pack was only a few degrees above ambient temp. With old lithium cells I watch the cell temps. If the cells stay cool everything is good. I had an ammeter connected between the packs so I could watch the current flow. In sport mode with WOT accelerating from 20 to 60 mph the current draw was around 35 amps. In standard mode under the same condition it was like 18 amps. I never use sport mode. At a steady 60 mph the current was only about 6 amps so the main pack is just sipping a little current from the extender. One interesting thing is that the average watts per mile shows lower than usual because the bike only sees the current flowing from the main pack and is comparing it to the miles traveled so the range estimate goes up accordingly. That all works perfectly. I you used higher capacity cells you could fit 2KWH in this space.

[ESokoloff]

“ bike only sees the current flowing from the main pack”

How/where is the extender connected?

How many parallel cell arrays there?
Earlier I had guessed 4 but relooking the math it seems like 6@28 cells.
If so, what is each cell capable of flowing (both in & out)?
35 amps divided by 6 is 5.83 amps which seems pretty high for a single 18650 cell.
Granted in normal use is only for a short time.
Figure out what a single cell is capable of in/out put & multiply by 6.
Use that figure as the max fuse ampacity & maybe de-rate that a bit for safety & use a time-delay fuse to allow for brief accelerations. 

[Specter]

that sounds about right there.,  most of the high current is the acceleration to get to speed, once you get there it pretty much sips and bounces back and forth really.  i wouldn't worry about the occasional heavy draw from romping it, as its only in that state for what 25 to 30 seconds, not enough to really steam the battery up,  the only time you would really need to be concerned is if you are doing a lot of throttle movement, even at lower speeds, or stop and go, as that is constant heavy in/out in/out.   Of course if you were running 90 mph then yah, might want to watch the current there too.


2500ma is it a standard capacity/use cell or a high drain.  being its older thats sounding llike a run of the mill cell there.  do you remember what you salvaged them from?  even the lighter use cells are good for 3 to 5 c, with some of the heavier duty cells able to take 20 c or more.


also what gauge wire did you use to hook it to the main pack with, just curious.  id not use less than 6 ga tbh.  fuse it at 50-60 amps and you should be good, this should also take an extended hard regen back into them as well.  make sure you use a dc rated fuse too, in case something does go bad, a wire pinches and shorts etc, the fuse can safely quench that arc when it lets loose.

sounds like you did a really good job here on this.  i love hearing people putting new gadgetry together, especially when they are repurposing old batteries etc,  good job there!

aaron

[electrictwowheeler]

The connection point is where the buss bars connect to the controller, so on the controller side of the main contactor. On gen 3 bikes the controller is under the battery. It's the easiest place to connect and has the advantage of not being always hot like it would be if you went direct to the battery. I already had a connection there that I use to connect an offboard charger. Like the brown Anderson connector on the Gen 2 bikes that you could  use to hook up an extra charger to. (that is a whole other story) I just split that and ran wire up to the tank storage.

I used # 10 boat cable which has an ampacity of 80 amps and is made with fine tinned wire. The wire run is about 4 feet in each direction.
The cells are LG M26 out of recycled stand up scooter packs.
The main specs are 2500mah nominal, max discharge 10 amps, max charge current 1C, Max operating temp 140 F
60 amp fuse
The pack is in two halves connected together by the contactor. 6p14s X 2 in series.

The whole thing is on the light duty side for sure but I always use a custom mode with the power the same as Standard Mode but with 70% regen on the throttle and 100%on the brake. In my test I never saw more than 20 amps in my custom mode and that was full throttle.

[ESokoloff]

So you’ve connected on the load side of the contactor at the input of the controller.

I would do what T.S. Zarathustra suggested.
Find a surplus rotary switch (OFF-ONE-TWO) & install a suitable resistor on the #1/BALANCE circuit that will allow main/extender balance. (Note that it would have be be rated for 125VDC).
It would be nice to find one that is sequential so the batteries are balanced before direct connection.
A surplus analog voltmeter installed across the two packs would let you know when it’s safe to rotate the switch to #2/RUN position

I would use a FLNR-35 or 40 amp fuse as it is a timedelay fuse with a 125vdc rating.
In the AC side of wires, #10 is limited to 30 amps so I wouldn’t feel comfortable pushing much past that & your testing shows it’s not necessary. 
AC motors have upwards of 7x inrush current to start (compared to RLA [Running Load Amps]) & these fuses are used. 

[electrictwowheeler]

So you’ve connected on the load side of the contactor at the input of the controller.

I would do what T.S. Zarathustra suggested.
Find a surplus rotary switch (OFF-ONE-TWO) & install a suitable resistor on the #1/BALANCE circuit that will allow main/extender balance. (Note that it would have be be rated for 125VDC).
It would be nice to find one that is sequential so the batteries are balanced before direct connection.
A surplus analog voltmeter installed across the two packs would let you know when it’s safe to rotate the switch to #2/RUN position

I would use a FLNR-35 or 40 amp fuse as it is a timedelay fuse with a 125vdc rating.
In the AC side of wires, #10 is limited to 30 amps so I wouldn’t feel comfortable pushing much past that & your testing shows it’s not necessary. 
AC motors have upwards of 7x inrush current to start (compared to RLA [Running Load Amps]) & these fuses are used.

Thanks for the suggestions. I think I'll just charge the batteries to the same voltage before installing the extender. My testing has shown that even with a 4 volt difference the inrush current is only 10 amps, well within the systems rating. I use a variable power supply for charging so it's super easy to get the packs to the same voltage. There is really no space left in the storage area for more hardware. The wire I am using is not SAE wire. Google "Ancor marine cable" and look at their wire size selection tables. I misstated the ampacity in my previous post, its 60 amps, not 80. Ampacity is defined as the maximum load a wire can handle continuously and stay within temperature specs. The marine wire has a larger cross section and higher temperature rating for the insulation than SAE wire. I like your idea of a voltmeter and have already ordered one to install on the extender. Easier than using a multimeter. I already have a voltmeter on the bike.
Yes, I have thought about installing a smaller fuse. That would be easy and now I know what the actual current flow is.
I would be more inclined to use a fast acting fuse designed to protect sensitive electronics. I'll think more about that.

[ESokoloff]

I googled
https://www.google.com/search?q=Ancor+marine+cable+rating&client=safari&hs=9M3p&sca_esv=dc3936d1c026acb1&hl=en-us&ei=g9Upas7_DbvIkPIP7IuAmA4&biw=430&bih=730&oq=Ancor+marine+cable+rating&gs_lp=EhNtb2JpbGUtZ3dzLXdpei1zZXJwIhlBbmNvciBtYXJpbmUgY2FibGUgcmF0aW5nMgUQIRigATIFECEYoAEyBRAhGKABMgYQABgWGB4yBhAAGBYYHjIIEAAYFhgKGB4yCxAAGIAEGIYDGIoFMgsQABiABBiGAxiKBUivMFCQCljVHHADeAGQAQCYAV2gAcQEqgEBN7gBA8gBAPgBAZgCCqAC6wTCAgoQABiwAxjWBBhHwgIXEC4YsAMYuAYY2AIYyAMY2gYY3AbYAQHCAgUQIRirAsICBRAAGO8FwgIIEAAYgAQYogSYAwCIBgGQBg26BgQIARgZkgcCMTCgB94nsgcBN7gH4ATCBwUwLjIuOMgHIIAIAA&sclient=mobile-gws-wiz-serp#lfId=ChxjMe
and still only see a 40 amp rating (at least it’s better then 30).
In the AC world, the circuit breaker protects the wire & the fuse protects the device. 
In your case, the fuse must protect both. 

FRN fuses are readable available….
https://www.homedepot.com/pep/Cooper-Bussmann-FRN-Series-35-Amp-Brass-Time-Delay-Fuse-Cartridges-2-Pack-BP-FRN-R-35/100184701?g_store=&source=shoppingads&locale=en-US&fp=ggl&pla&mtc=SHOPPING-CM-CML-GGL-D29K-059_027_S_O_WIN_CVR-NA-NA-NA-PLA-7087500-NA-NA-NA-NBR-NA-NA-NEW-PRIO_FY26&cm_mmc=SHOPPING-CM-CML-GGL-D29K-059_027_S_O_WIN_CVR-NA-NA-NA-PLA-7087500-NA-NA-NA-NBR-NA-NA-NEW-PRIO_FY26-23586043094-191837963685-294682000766&gclsrc=aw.ds&gad_source=1&gad_campaignid=23586043094&gbraid=0AAAAADq61UddcvSEfqqN_ptK4MEaOPKkf

As far as protecting electronics, I’m not sure how this applies as from what my minds eye sees (over the internet) your not subjecting the system to more voltage then it normally is subjected too. 


Can you charge both batteries out on the road with the on-board charger?
Will that overload the charger?

Is the only time you have to worry about Delta V is upon installing the fully charged (off the bike) extender?
The extender is only installed when you know extra range is needed?

Yeah, sounds like you don’t need the extra components but I would still consider dropping the fuse size but it’s your project so your piece of mind is what matters.

[electrictwowheeler]

I googled
https://www.google.com/search?q=Ancor+marine+cable+rating&client=safari&hs=9M3p&sca_esv=dc3936d1c026acb1&hl=en-us&ei=g9Upas7_DbvIkPIP7IuAmA4&biw=430&bih=730&oq=Ancor+marine+cable+rating&gs_lp=EhNtb2JpbGUtZ3dzLXdpei1zZXJwIhlBbmNvciBtYXJpbmUgY2FibGUgcmF0aW5nMgUQIRigATIFECEYoAEyBRAhGKABMgYQABgWGB4yBhAAGBYYHjIIEAAYFhgKGB4yCxAAGIAEGIYDGIoFMgsQABiABBiGAxiKBUivMFCQCljVHHADeAGQAQCYAV2gAcQEqgEBN7gBA8gBAPgBAZgCCqAC6wTCAgoQABiwAxjWBBhHwgIXEC4YsAMYuAYY2AIYyAMY2gYY3AbYAQHCAgUQIRirAsICBRAAGO8FwgIIEAAYgAQYogSYAwCIBgGQBg26BgQIARgZkgcCMTCgB94nsgcBN7gH4ATCBwUwLjIuOMgHIIAIAA&sclient=mobile-gws-wiz-serp#lfId=ChxjMe
and still only see a 40 amp rating (at least it’s better then 30).
In the AC world, the circuit breaker protects the wire & the fuse protects the device. 
In your case, the fuse must protect both. 

FRN fuses are readable available….
https://www.homedepot.com/pep/Cooper-Bussmann-FRN-Series-35-Amp-Brass-Time-Delay-Fuse-Cartridges-2-Pack-BP-FRN-R-35/100184701?g_store=&source=shoppingads&locale=en-US&fp=ggl&pla&mtc=SHOPPING-CM-CML-GGL-D29K-059_027_S_O_WIN_CVR-NA-NA-NA-PLA-7087500-NA-NA-NA-NBR-NA-NA-NEW-PRIO_FY26&cm_mmc=SHOPPING-CM-CML-GGL-D29K-059_027_S_O_WIN_CVR-NA-NA-NA-PLA-7087500-NA-NA-NA-NBR-NA-NA-NEW-PRIO_FY26-23586043094-191837963685-294682000766&gclsrc=aw.ds&gad_source=1&gad_campaignid=23586043094&gbraid=0AAAAADq61UddcvSEfqqN_ptK4MEaOPKkf

As far as protecting electronics, I’m not sure how this applies as from what my minds eye sees (over the internet) your not subjecting the system to more voltage then it normally is subjected too. 


Can you charge both batteries out on the road with the on-board charger?
Will that overload the charger?

Is the only time you have to worry about Delta V is upon installing the fully charged (off the bike) extender?
The extender is only installed when you know extra range is needed?

Yeah, sounds like you don’t need the extra components but I would still consider dropping the fuse size but it’s your project so your piece of mind is what matters.

Whatever the rating is we agree that the wiring is adequate.

Yes, both batteries charge together from the onboard charger. The charger will charge at the same rate as always, 1,3 KW on 120v and 6KW on 240v. It will take slightly longer to charge.

Yes, I'll only use it when I'm going on a longer trip.

The voltage difference is a problem when the packs are connected together for the first time and also if the bike sits for a long time with the extender installed because they are only connected when the bike is keyed on or charging and the extender contactor is closed. I don't see this as a problem though because it would probably take months for the two packs to get more than 4 volts apart and I don't envision long term use of the extender. They both have very slow self-discharge rates.
 
Reducing the fuse size sounds like a good idea.

I did a hundred miles today, mixed riding. Worked perfectly!

[Specter]

Even though it's boat cable, which has a higher rating than standard building cable, 80 amps is pushing it, unless it's a fairly short run, like a few feet jump to a starter or only intermittent use.  otherwise it's typically rated at around 60, would be derated to around 50 or so in an engine compartment due to temperatures being hotter. Given it's boat cable, as you claim, it is being rated using marine standards ABYC instead of normal NEC standards for buildings.  nec would rate it only around 30 amps for open 10ga wire.

 if you have it up under cowling or in a box, might want to keep that in mind but I don't think that'll really be an issue for you, you won't be seeing those kinds of amps very often at all.  No need for switches and stuff, just more stuff to add resistance and corrode on you.  Tinned wire is a good thing, fine wire is even better, its easier to work with.  personally i love using welding cable when i can get away with it. 

it's up to you but a simple Anderson connection might be a quick and easy way to connect / disconnect it, and you can even put the fuse inline with it.  that way you are not playing with nuts and bolts, stretching threads and up in that stuff every time you want to use it.  an Anderson would also protect the disconnected ends too from most accidental shorting.

the lg batteries tend to be one of the higher grade batteries on the market, so you are good there, and yes, charging, most manu's prefer 0.5 to 1 C but will allow a bit more safely.  10A - 4C discharge, yah that right in range with a standard grade battery,

another place to look for cheap batteries, sometimes you get good finds, is portable tools, people hunk the pack because one cell dies and it kicks the whole pack but the rest of the cells are usable.  home depot, lowes, or placesl ike that often have free battery disposal, and a quick talk to the manager, many times they are more than happy to give the old ones for free, because they have to otherwise pay to dispose generally.  depending on what brand, size etc, the cells vary but you can build plenty of 'aux power' for essentially free.

aaron