Paralleling BMS protected Li-ion packs.

[AZguy]

Hi AZguy - would a solid state solution require a heat dissipating mount point (such as the seat tube bottle mounts)? I do think there's a market for a plug-n-play dual battery box that offers ether Anderson or XT-90 connections - add a USB charging socket to further sweeten.

Solid state will have to shed heat

I've got a project like this on my back burner... seems every time I get back into it I get distracted by something else - regardless the critical part has always been the thermal portion of the solution and the rest is pretty easy

[ncmired]

The power that a passive switch has to deal with is quite high and switches rated for it are very expensive and on the large side of things - it better be break-before-make!

I carry two batteries mounted to my bike and switch between them by very simply changing which [XT90s's] connector the controller is plugged into... easy peasy, takes seconds, looks very clean, they handle the power and are very inexpensive

IMO the only good reason to parallel batteries is if you need more current than one can provide, and even then, not for me, I'd just budget a proper battery for the application

I was working on a solid-state solution a couple of years ago and recently dusted it off because my business slowed to a crawl and I prefer to stay busy... It's non-trivial to pull off a cost effective approach... I may look into a load share solution but that's for another day...

Hi AZguy - would a solid state solution require a heat dissipating mount point (such as the seat tube bottle mounts)? I do think there's a market for a plug-n-play dual battery box that offers ether Anderson or XT-90 connections - add a USB charging socket to further sweeten.

[Gr8fun]

How many kwh are you running?
do you still use your solar panels?
sorry just read you are using panels.
Any changes in past year.?

[Gadgets4grls]

That is what I've done. I have four Lunacycle Wolf 52V batteries in parallel through Schottky diodes on the output side of the BMS.
The charge side are just connected in parallel. I went this way as the diode will cause a voltage drop and didn't want the interference with the charge controller. I have both AC as well as solar charging.

I recommend you use matching batteries with similar recharge cycles.

[wozzlegummich]

Would love some input on my take/idea/plan for permanently connecting a second battery.

[philipgaines]

Ar-r-rgh! Yes, I meant 48v for B2 also.

[Fred]

I’ve read through the whole forum and can’t find an answer to my question. I have two 48V 13Ah batteries, one original on my Rad Runner. Can I wire a three way battery switch, #1, off, #2, to my two batteries? The USAF sent me to a 10 month electronics school in 1968, in the last class they said there is a new device coming out called a transistor. Things have changed. I was thinking of using a boat battery switch, are there smaller switches? Thanks.

Here is one that I was considering, but decided not to use:
https://www.amazon.ca/dp/B01J31PRBS/ref=dp_cerb_1

It is rated at 12V 25amps. Obviously most of us are at 48V or more, but I believe there is a good chance it would suffice as long as your drawing less than 25 amps. I have one, but as I say, have decided to go the unplug/replug route for now. After all, I will be switching infrequently -- only if I run out of juice on a long trip.

[AZguy]

Wouldn't advise it - worst case it could short the capacitor... they're just rolled up layers of metalized dielectric... but they're not much more susceptible to damage than most any other electronic component outside the points I made

If their voltage is exceeded they tend to explode and the little scores on the top of the can is to make that not happen catastrophically (i.e. shrapnel) which is a good reason not to have the tops under a hard potting - I don't know what kind of potting that is

I've seen a lot of vehicle products with them and I've seen them shake off the PCB's when they aren't attached well which is by far the greatest issue... I don't like their temperature and aging concerns either, especially cheap ones - I usually go for tanatalums but they are too expensive for high capacitance in the higher voltages like we see

[ncmired]

Hi AZguy, on those aluminum electrolytics what would happen if the exposed part of the can was dented?

[AZguy]

I was thinking the same, connecting up a 48V to a 38V might even make the news - and as my primary flight instructor said to me, we aren't the kinds of guys that want to end up in the news

For what it's worth, those aluminum electrolytics "fragility" tends to be how they're soldered to the PCB and it looks like there's potting all over the bottom of them where they attach so not so fragile

However, as an aside I personally try to avoid using aluminum electrolytics anywhere - along with the mechanical issues of how they get attached to the PCB they don't age that well, especially cheap ones and in high temperatures, but if you need a lot of bulk capacitance at higher voltages, there's little other choice... but potting them, even if just the lower half, will make them rugged mechanically

That device looks like it may serve the or'ing diode function - hopefully with MOSFET's actively driven instead of diodes

[ncmired]

What's the voltage drop across those 30amp diodes?

I've looked a little at the Watt Wagons dual battery converter (https://wattwagons.com/collections/a...tery-converter), which may have some switching logic.

P.S. not sure why Watt Wagons placed those fragile can capacitors out in the open like that.

[Sebz]

I hope you meant that B2 is 48V and not 38V or you are in for a bad surprise

[philipgaines]

I just completed what so far appears to be a successful addition of a second battery in parallel. B1 is 48v 8.7ah; B2 is 38v 12h. In the first test, B2 would want to charge B1 when not under load, e.g., while coasting—which is not a problem electrically or safety-wise. But my controller would start reading charge mode, and when the balancing between the two batteries was done after a few seconds, it would revert to assist mode at the zero level, and I would have to reset the assist level to what it was before the charging happened. Unacceptable. So I installed a 30amp diode on the discharge wire of each battery to block the B2 to B1 charging. The charging stopped, so everything seems to be operating just like before the B2 addition.

However, I haven’t done a long ride yet, and something has me nervous: On my short test drive (3 miles) the range readings at the various levels did not go down at all, so I’m wondering if my set-up is confusing my controller. The range readings on full charge are still the same as they were with one battery, which doesn’t surprise me since the controller is only wired to B1 and I know that B2 is discharging under load, so it’s not clear to me what’s going on. A long ride might tell me more.

[calfee20]

I’ve read through the whole forum and can’t find an answer to my question. I have two 48V 13Ah batteries, one original on my Rad Runner. Can I wire a three way battery switch, #1, off, #2, to my two batteries? The USAF sent me to a 10 month electronics school in 1968, in the last class they said there is a new device coming out called a transistor. Things have changed. I was thinking of using a boat battery switch, are there smaller switches? Thanks.

I have not done this but here is a thread that touches on this. This thread goes back to 2016.

https://electricbike.com/forum/forum...eed-more-range

[AZguy]

Battery 1:



Battery 2: