New kind of build coming 
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Why though?!?
For days when one charge isnât enough and ainât nobody got time to wait
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So how big is the battery in there and if it doesnât to 40v how long will this top it off?
I built a little scooter off of a Razor Pocket Mod because of @monsterbuilder
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Battery is 12s6p p42a
Currently getting it as low as i can so that i can science a 0-100% turbo charge
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Less resistance for the charger bypassing the BMS.
I like lowering my target voltage to about 4.15vpc when charging at high rates.
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Oohhh. I bet that trail is fun on those wheelsâŚ
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Errr its bearable 
the rocks are just a little too big. Totally not doable on urethane tho, so iâm grateful for these wheels
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Weâre fully milked. Gonna let the pack cool down a bit, then itâs time for turbo juice science.
Was Rooâs longest run yet. We went to and back from the dog wash, the ultimate deception. At least 16km she just ran. Not bad for just a little woofer!
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the chargers will cut off when the current from them slows down to some threshold. (typically)
so the two chargers together could:
A. stop together, a little bit earlier than full charge. (probably negligible)
B. one stops because itâs low current threshold is hit first which gives more headroom for the other one to keep going til done.
I think B is the weirdness youâre asking about. and I suspect itâs more likely.
details:
- The chargers limit current and voltage all the time. it results in cc/cv but you can think of them as just limits.
- while the current flows it pushes the voltage up relative to the amount of current. more current more voltage rise.
- total voltage with the charger attached is the SOC voltage of the cells + the voltage rise from the charger current .
- when total voltage is < 4.2v/cell the charger puts out itâs max current. (CC mode)
- when total voltage is > 4.2v/cell the chargerâs voltage limit kicks in (CV mode) in and current is ramped down as the cells SOC rises. note, it slowly ramps down current keeping the total voltage close to 4.2v/cell lowering charge voltage rise as the SOC voltage increases.
- typically chargers stop when this current drops below some minimal level. importantly not based on voltage, which is hovering around 4.2v/cell ever since it hit âCV modeâ.
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This 20a charger is kinda cool and respectful of the battery. It ran in âpre-chargeâ mode at 5a until battery hit 40v and then it ramped up to the full 20a.
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I used to live on Lead acid 12v batteries, and had many different charging sources going at the same time. In order to get good longevity deep cycling, Lead acids one needs to charge them to full ASAP after any discharge, but while Lead acid full charge resting voltage is ~12.8v, one needs to bring them upto the Mid 14âs for a period of time, until amps tapered to low levels.
In lead acid world this is called the absorption stage and is the constant voltage stage.
With two chargers set to say 14.6v, there could be this weird oscillation between charging sources when it got close to 14.6v. One charger would cut out, and the loss of current would cause voltage to fall and the charger which cut out might then kick back in and confuse the other charger which had been sharing the load, but then had to go back to constant current with all it had, which then confused the other charger, and back and forth.
It was highly dependent on the charger and would change as the batteries aged and their resistance increased. I really needed to have an ammeter and a voltmeter on each charging source, and basically gave up on automatic in favor of manual voltage control which was a good learning experience.
When I got into Esk8 and started learning the trends and tendencies of lithium charging I noticed some similarities, and a lot of differences, but have not tried to combine charging sources.
I have noticed the chargers which came with some cheap 7s junk, which were supposed to be 29.4v max and claimed to be so, were actually well over 30v, and entirely dependent on the BMS to cut power. Those chargers would just bring the battery to and then keep the battery at 30.32v for as long as they were connected together.
I limited it to 29.4v with a bucker and noticed the chargers red light would turn green when amps tapered from 0.32 to 0.31. But amps would keep tapering to 0.00X.
3 different 7S âchargersâ did the same exact thing. They look identical to what I see come with a lot of premades and Ebikes and scooters.
Iâd urge everyone to actually check the output voltage and the Amperage of their charger, especially if it is just red light/green light.
I use inline wattmeters and feel absolutely blind without knowing how many amps are flowing at the voltage.
My charging sources now are all CC/CV voltage boosters. Mostly I boost from lead acid float charging voltages, from the 8 year old AGMS on my garage floor which are still healthy enough. I twiddle the voltage pot and current pot basically every single time I charge, based on when I expect to need to ride again, and charge as fast as needed but as slowly as possible, any often charge to only 4.1 volts per cell when I donât need the full range.
I always watch the inline wattmeters and will set an alarm on my phone to remind myself to disconnect after X amount of time, especially important if I have it set to 4.2 volts per cell, and I really try and not let amps taper to below 0.2 on my 10s2P BAK45D battery.
One of my boosters has a third potentiometer which lets me dial in when the red light turns green based on Amperage, but this one can only do 150 watts. ~400 watts is around the limit of my BMS and charge port, and is about a 1C charge rate, and I do have a booster capable of that, boosting from 12.2v.
I do notice amps start tapering a bit before the battery reaches the chosen voltage, if I have 4.2 volts chosen, once it gets to 41.76 or so then amps start tapering, and my previous 10S battery started to taper amps earlier and earlier as it ages and resistance increased.
I now have a direct ESC/battery XT90 panel mount, and could do what Al is currently doing, bypassing the BMS for charging above the rating of my BMS and charge port, but Iâd not feel comfortable allowing greater than 41 V without the BMS there to stop things if one Pgroup is well above the others.
So far every time I have manually checked balance it has been very close, but I only have a dumb Daly BMS, so I do not check often.
This BMS only starts balancing, at 4.18v so when I want to balance, I often will charge somewhat fast to 4.15, then very slowly to 4.18, then 4.185, then 4.19, 4.19 then 4.20 at like 3 watts.
I love having voltage and current potentiometers and donât really trust any automatic charger to do what it says it does. I am far too suspicious from my lead acid days and the ridiculous claims of the marketing material of the latest and greatest chargers.
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Just took the mach for a somewhat spirited ride and battery temps look higher after the ride than they were after the turbo charge, so iâm feeling pretty good about that.
What iâm not feeling good about is the zmote.. i had some weird remote fuckery happening a couple weeks ago on a group ride, as well as several weird fuckeries just now at heavy throttle/full speed scenarios.
I like the dual trigger, but thereâs been one too many weirdnesses with it now for me to trust it.. i feel like going back to the puck is the way forward
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Bummer dude.
I now have I think 4 broken Z-motes. Different issues. Canât really think of one similar to yoursâŚ
Last one the throttle doesnât work⌠only the brakes.
Yeah i dunno what the deal is but it seemed like it just cut out completely and didnât work again until i let go of trigger and pulled it again.
Too uncertain for me, going back to puck
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Yeah. i glossed all these concerns with the word âtypicallyâ. :D. felt i had already wrote too much. 
but yeah, they might not cutoff ever. just turn on the done charging light but still ramp down current infinitely.
and if they do cutoff off they might restart for some reason, and oscillate with the second charger. but i suspect thatâs more rare. i think tiâs either they donât cutoff as you observed, or they do and wait for power cycle or disconnect to restart.
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I didnât heed my own caution when i did the turbo charge and rather just observed VERY closely what was happening at the top of the charge.
Interestingly, the 20a charger went into CV mode well before the 12a charger did and also lowered itself to a more conservative current than the 12a.
The 20a charger was the first to switch itself off, at around 50.2v (at the bms). As soon as it turned off, i disconnected it, but there was no sign of anything fucky happening.
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