One charge controller, two battery banks

[hour]

So I have a knock off pelican case with a battery inside, and want to put my charge controller inside too. The PV input will feed through some panel mount connector on the side of the box.

Thing is, I have another one of these portable (less portable) battery packs and don't really want to buy another charge controller for it. I'm fine with charging them one at a time.

My thought is that I can have another panel mount jack on the side of this first portable battery that I can plug a second battery pack into, which will also connect to the charge controller's B+ and B-. But not simultaneously.

I think I need a switch for this, where toggled one way will just let the internal battery charge, and toggled the other way will switch completely over to the pack plugged in to it. No paralleling the batteries or anything. One or the other. I'll disconnect the PV input before I switch from one to the other of course.

Is an SPDT switch what I'm looking for? I figure if I use a switch rated at 10a or so that doesn't appear to be total crap, I can run things straight through it. The max charge current to either battery will be limited by the charge controller, at about 5 amps.

 

[john61ct]

Blue Sea is my goto for robust high-amp battery switches.

Maybe an A/B/Off design is enough, but check out the 1/2/Both versions as well.

There is nothing wrong with charging both banks off one source - or multiple disparate sources - at the same time, as long as they share similar voltage setpoints.

 

[hour]

Blue Sea is my goto for robust high-amp battery switches.

Maybe an A/B/Off design is enough, but check out the 1/2/Both versions as well.

There is nothing wrong with charging both banks off one source - or multiple disparate sources - at the same time, as long as they share similar voltage setpoints.

Was looking for 1/2/OFF and all the search results were muddled with 1/2/Both, and I didn't want to accidentally flip to both - or have someone else at my camp screwing around with it. And they're all a little large considering this battery pack is in something the size of a small pistol hard case.

Heck, I'm even a little wary of having an OFF setting, I seem to recall reading that it's a rather bad thing to have your PV input cranking without a battery attached and an off setting just adds another position to the switch that could/would mean battery disconnected. The capacity of each pack is identical, both LFP, but they may frequently be far apart in voltage. I'm using pretty small jacks and wiring for this with a target charge rate of ~70w and would imagine I'd have to scale that way up to handle two packs trying to equalize.

On the fence about this now and might just put the controller in a dedicated smaller pelican case knockoff. The original plans benefit was having one less black case to carry around, but I've now imagined too many scenarios where I'd want the packs on opposite sides of camp. Whichever one is by my truck may as well be charging from the solar surplus. Hell, that's why I built two packs in the first place instead of one large one.

Thanks for suggestions guys

 

[john61ct]

Under 3" square, model # 2006, on / off, one per bank, remove and stow the knob for the internal one.

Robust wiring so you don't worry about the paralleling, switch can handle it, 300cont./500 for 5min / 900A rated for 30sec.

Or go to an ACR for the external one, auto-on but only after voltage goes high, otherwise keeps isolated. BSS again, my pref is the ML version.

 

[hour]

Whats max. current you expect to charge at ? Initially mentioned 5A...
A 20A SPDT maintained & center off (or not) toggle or rockerswitch is about 10$ If you really need higher, you can use DPDT and double up its contacts and its still in a fairly small footprint.

Accidental switching to off and pissoff the controller scenario exists regardless if the switch has a center off position or not.
If switched to external battery, and external battery is not connected, is same thing seen by controller as switching to ‘off’ position.
Further, unless you use a form “D” toggle switch, a brief moment exists where no connections exist.

Something like 5a... the controller and the battery could handle a lot more but I'll never be in a hurry to get them charged. They'll most commonly be charged from USB-C PD -> 2.1x5.5mm 20v output feeding in to the controller as PV. This dongle thing has an inline module that negotiates the voltage output of 20v from a USB C PD 12v charger. This is my inexpensive solution (not concerned with efficiency loss) to accomplish B2B charging, from big house lifepo4 to the little ones. The 12v PD charger I have maxes 20v@4.5a but I'm happy with running well below that, regulated by the max charge current setting of the charge controller. TL;DR 5-6 amps, 60-75w.

My issue with the OFF selection wasn't really in thinking about the slide-switch things where OFF is in the middle. It was having a giant red knob on the side of the box and someone's kid cranking on it with potentially two positions that would result in a battery disconnect. Honestly I shouldn't be sweating this, I'll know to disconnect charge input before switching batteries and if I were really smart I'd just hide the switch inside the box. The form factor of the rectangular switches that have OFF in the middle is ideal, 1cm protrusion off the box if mounted externally. I know from experience that the circle panel mount switches with the plastic tabs on the side to grab the panel are always a letdown, so I'm avoiding those... and ones with a half inch long flipper.

Under 3" square, model # 2006, on / off, one per bank, remove and stow the knob for the internal one.

Robust wiring so you don't worry about the paralleling, switch can handle it, 300cont./500 for 5min / 900A rated for 30sec.

Or go to an ACR for the external one, auto-on but only after voltage goes high, otherwise keeps isolated. BSS again, my pref is the ML version.

That's certainly better if the knob can be removed. The robust wiring part means robust connections, and my desire to have panel mount jacks for inlets and outlets limits me. I don't know if there's something similar to the ever common 2.1x5.5mm jack - but way-way beefier. Something tells me I'd end up using powerpoles for this and I still don't know what I could expect current wise of a 32ah battery near dead getting paralleled to a 32ah battery near full. It's just a lot of fuss to achieve simultaneous charging of both packs with one charge controller, when I'm content doing one at a time at a mild charge current through tidy connections. I'd give this and pricy B2B solutions more consideration if the packs anything more than unnecessary glorified power banks, built for the experience/curiosity/hell of it.

Thanks to both of you, if it stops raining on the weekends (#@%! 82*F during week, 42 and rain on weekends, always) I'll get to test out whatever I settle on.

 

[john61ct]

Anderson connections are the standard, can convert to a ciggie pigtail for guests.

Link to your Type-C PD charger?

 

[hour]

Anderson connections are the standard, can convert to a ciggie pigtail for guests.

Link to your Type-C PD charger?

I have a few Anderson things but the 30a plugs are just a pain in the the ass even with the $50 crimp tool. Maybe I'd like em more in 45A. I've switched to XT60 for most stuff now but they don't feel good at the end of a home made extension cord. Andersons never really have either. Damn, almost making me miss SAE. $10 for a 5 pack of panel mount connectors with rubber cover, readily available extensions in any length imaginable, and can be had in 10 awg for short lengths and 10-14 for longer.

5V 3A, 9V 3A, 12V 3A, 15V 3A, 20V 4.5A LINK ($45) Wire to cig plug is 16AWG
Will cut the cigarette plug off and install XT60 connector, but even so it's better quality than most cig plugs I've seen really ever.

9v 12v 15v 20V USB negotiator spoof trigger whatever (this one is preset to 20v but could be changed if case cracked open) LINK ($9)
Standalone board LINK ($3.88)

Good video on the board in use

 

[john61ct]

Great stuff, thanks.

+1 on chopping stock ciggie connectors

5A load with the BSS locking version, maaaybe 8-D

 

[dwh]

If you're switching B+ and B- ... you'll need a double-pole.

And a single-pole to disconnect the solar.

Switch off solar, flip to other battery, switch solar back on.

Personally, I have my doubts that having the solar connected without a battery will do any damage to the charge controller. They all recommend hooking up the battery then the solar, but that's because they get their power from the battery. Solar without battery...most likely just doesn't do anything but sit there looking stupid.

But adding a switch to kill the solar while switching batteries is cheap insurance...and you'll have your tools out anyway.

 

[IdaSHO]

I have a few Anderson things but the 30a plugs are just a pain in the the ass even with the $50 crimp tool. Maybe I'd like em more in 45A. I've switched to XT60 for most stuff now but they don't feel good at the end of a home made extension cord. Andersons never really have either. Damn, almost making me miss SAE. $10 for a 5 pack of panel mount connectors with rubber cover, readily available extensions in any length imaginable, and can be had in 10 awg for short lengths and 10-14 for longer.

5V 3A, 9V 3A, 12V 3A, 15V 3A, 20V 4.5A LINK ($45) Wire to cig plug is 16AWG
Will cut the cigarette plug off and install XT60 connector, but even so it's better quality than most cig plugs I've seen really ever.

9v 12v 15v 20V USB negotiator spoof trigger whatever (this one is preset to 20v but could be changed if case cracked open) LINK ($9)
Standalone board LINK ($3.88)

Good video on the board in use

FYI, I've been running the same charger, though for my Lenovo X1 Carbon for a few years now.

So far so good. It keep the power hungry X1 Carbon happy. And the cig lighter attachment is decent.

For my usage, Ive never felt the need to change it out.

 

[hour]

If you're switching B+ and B- ... you'll need a double-pole.

And a single-pole to disconnect the solar.

Switch off solar, flip to other battery, switch solar back on.

Personally, I have my doubts that having the solar connected without a battery will do any damage to the charge controller. They all recommend hooking up the battery then the solar, but that's because they get their power from the battery. Solar without battery...most likely just doesn't do anything but sit there looking stupid.

But adding a switch to kill the solar while switching batteries is cheap insurance...and you'll have your tools out anyway.

Well, one would think. Two or so years ago I was on a road trip and noticed my fridge wasn't at the set temperature at a rest stop, like 20 degrees above but actively running with compressor going. Then it cut off completely before my very eyes as stood over the roof top solar scratching my head. The old battery had shifted in my truck a couple of inches and popped the wire out of the ring terminals that lead to the charge controller. The fridge continued to run since I had it on the load output of the charge controller. So for who knows how many miles that day, I was intermittently powering my fridge without a battery No damage done, that's the same controller I've repurposed for the project in this post.

FYI, I've been running the same charger, though for my Lenovo X1 Carbon for a few years now.

So far so good. It keep the power hungry X1 Carbon happy. And the cig lighter attachment is decent.

For my usage, Ive never felt the need to change it out.

That's good to hear, as long as it keeps functioning I'll have no reason to change it out either. About as powerful as one can get.

Smallest Harbor Freight apache case now houses a Victron 75/15 with two 2.1x5.5mm metal female barrel jacks on the side. I haven't labeled them yet because I want something better than my chicken scratch handwriting... a solar sticker on one side and a battery sticker on the other or something.

Two circular vents are on the front of the box, and a 40mm exhaust fan on the back. The load output on the controller powers a thermostatic 12v module, which in turn powers the 0.1 amp fan. Charge controller is mounted on the bottom of the box but has 1/4" standoffs to elevate it a bit, and a bunch of holes are drilled directly beneath it so the fan will pull air from between the aluminum backing of the controller and bottom of box. That's also where I stuck the temperature probe for the thermostat control.

Works freaking perfectly. Obviously I decided against putting the controller in portable battery box A - just so I can use and charge the two packs completely independent of one another in terms of proximity. If the wires look small (18 gauge solid copper inlet, 16 gauge stranded copper output to battery) well, you're correct. Perfectly adequate for providing somewhere in the neighborhood of 60w.

(Pics incoming in a few minutes)

 

[hour]

Charging from a 87w macbook pro charger. So yeah, to accomplish B2B charging either inside my truck, or from its auxiliary battery in the bed, I just need to use my high powered USB C PD charger. Ignore filth, I absolutely destroy my coffee table and everything else whenever I do a project.

 

[hour]

I've seen 68w being supplied to the battery, limited by the charge controller's max charge current setting. Right here it's just floating along making up for the power I'm pulling out of the larger apache case... 20v negotiated from Macbook 87w charger.

 

[john61ct]

Many SCs will definitely fry disconnecting the battery while the panels are pumping current in.

A big make-before-break battery-type switch like Blue Sea makes will work fine, as will throwing a blanket over the panels.

But a switch does make things convenient.

 

[IdaSHO]

I use re-settable breakers to isolate panels from controller & controller from batteries

Makes servicing a breeze