Lithium Battery charging

Thanks Vic
Ya it is a pita. My two panels, one on roof 160 and one portable flex 100, are in parallel. Is it as simple as changing the plug on one to the opposite? (Plus minus) ... that is ... using a reverse male to female adapter. Or do I need to do some fancy rewriting?
I only use the flex panel when it is cloudier... so series would make more sense. In series the bolts are then additive say 9v on one and 8 v on the other if end up with 17v?
 
Have you tested your panels lately to ensure they are producing as they should? I am in the process now. I still need to dismantle my roof. Yesterday, I confirmed my portable, 100W flex panel, is producing ~44W during optimum conditions. Have not needed it, in the field, but not comforting info. I’ve not encountered prolonged solar depriving weather, so far, but I do want the option to enhance my capability.
If you switch over to series, it is my understanding, you will need a second, separate controller if using a secondary, exterior solar outlet. (Rear back wall of Camper) If your flex is indeed wired with your roof panel in series entering the roof outlet, in conjunction, you are OK. I chose parallel for the plug & play option with my rear outlet. Series is intriguing. Would higher outside temp, hot, be any kind of consideration with higher V?
 
You can do series... but that may have been a red herring I tossed out and not as critical as you might think given your low power production. Sorry.

The beauty of MPPT controllers is that they will massage the incoming power to feed the batteries what they most need... like Kobe beef!

So even if your one roof panel is only producing 80W (50% power) that will be converted to what the batteries need. If the battery is dead (11.5V) the MPPT will try and feed it at least 16.5V (5v more than it is at) 80w/16.5 = 4.8A.

Stokeme, I think your math is a bit wonky. Watts is Amps * Voltage. You mention 100W @24V = 100/24 = 4.167A. 200W at 12V = 16.67A.

Rob has 260W total available to him. Setting aside for a moment the difficulties of mismatched panels, lets say he hooks them up in parallel. Then he would be feeding 260W / 12.7V= 20.47A into the controller. (why 12.7? 12.2 is a discharged AGM battery... and the MPPT will always try to give the battery .5v more so that current can flow into the battery)

If he hooks them up in series, he will have 260W / 25.4V = 10.23A into the controller. (25.4V = 2x12.7v) The ACTUAL voltages and currents produced by hooking up in series and parallel are dependent on the specs of the panels, which we don't know right now.

In both cases, the MPPT will work to create what the batteries need. The series hookup gives the MPPT more room to play with, so is the preferred way to hook up panels to an MPPT controller.

There is a way to use the existing wiring in the camper to create a series connection vs parallel on your portable. I posted it some time ago, but my brain is futzed right now so I can't recall the details. It involved using a dongle....
 
Vic, I am confused about “more room to play with” concerning the mppt controller. I do not understand the inference. I do not understand why ... (series) less A with higher V, is better than ... (parallel) higher A with less V. To not hijack Rob’s thread any further, I will post some panel review findings & inquire more about series vs parallel. The plug & play back 2nd Solar outlet, allowed with parallel, is a big plus for me because Solar is my only form of energy replenishment. Thanks for the info on this thread.
 
Your explanation helped. I think my system is doing what it can but 4 days rain and canoes on has just squeezed the rocks dry. My battery did come back a bit on the drive with the camper main knob off. The alternator though good 140 amp is controlled by the truck computer and does not seem to put the juice through the separator .... maybe it is throttled.
The series option is out. I like to keep it as simple as possible. Weather and canoes on top did me in. Sun this afternoon should help.
Vic having s second battery would solve the lack of energy over time. We use mostly the isotherm small fridge and led lights, charge iPhone and iPad. I did revive that LiFePo4 DIY battery and will consider finding a place for it. Just 30 lbs more. Put the two in parallel.
Sounds nuts I know (the truck hood is hot ) but having the flex mounted on the hood would be a great solution to canoe on roof. Maybe a curved mount on canoes hull!!
Light canoes stay on roof when popping up.
IMG_0785.jpg
 
IMG_0829.JPG
Just thought I’d post controller shot Sun not out yet but trying. I see there is less than 4v difference. The camper main knob is off.
 
I think there is a little confusion on how solar controllers/chargers work. The controller will try and output the set-point voltage for what ever stage of charge it is in (eg 14.4V in bulk/absorb or 13.4V in float). It won't try and add anything to this. However during the bulk phase of the charging the battery voltage is lower than the controller set-point, so the battery pulls the controller output down to what ever voltage the battery is at, and the controller provides as much current as it can up to the current limit (this is the Constant Current or CC phase). On an AC charger the current is limited by the controller to what ever its rating is (eg 30A on the IOTA). On a solar charger the current is more likely to be limited by the power available from the solar panels. Once the voltage has reached the absorb voltage, then the controller starts regulating the voltage (for example to 14.4V) until either the absorption phase times out or the current decreases to a certain amount (this is the constant voltage phase or CV) The charger then drops back to float and regulates the output voltage to whatever the float voltage set-point is (eg 13.4V).

The 5V difference is likely a miss-reading of the MPPT specs. The MPPT won't start until the solar panel voltage is 5V higher than the battery in order to insure there is enough power available from the solar panel to actually charge the battery. Before the MPPT starts, the panel is producing Voc. If you tried to start charging as soon as the Voc > Vbattery, as soon as you loaded the panel down by turning on the charger, the panel voltage would drop below Vbattery and you would need to shutdown. The 5V buffer prevents this power wasting 'short cycling'. Once the MPPT is charging, it will continue to run until the input voltage is down to ~ V battery + 0.7V, which is the diode drop inside the MPPT buck converter.

Happy Canada Day!
 
Great detail I need to know. Thanks Lars. To expand my capacity for four days of rain I am thinking of adding my newly reborn DIY LiFePo4 battery in parallel. I have a good BMS but need to know if it is okay to do this with a Battleborn (in parallel)... does the BMS of the dyi need to match the specs in the Battleborn? Any possible snafus?
 
buckland said:
Your explanation helped. I think my system is doing what it can but 4 days rain and canoes on has just squeezed the rocks dry. My battery did come back a bit on the drive with the camper main knob off. The alternator though good 140 amp is controlled by the truck computer and does not seem to put the juice through the separator .... maybe it is throttled.
The series option is out. I like to keep it as simple as possible. Weather and canoes on top did me in. Sun this afternoon should help.
Vic having s second battery would solve the lack of energy over time. We use mostly the isotherm small fridge and led lights, charge iPhone and iPad. I did revive that LiFePo4 DIY battery and will consider finding a place for it. Just 30 lbs more. Put the two in parallel.
Sounds nuts I know (the truck hood is hot ) but having the flex mounted on the hood would be a great solution to canoe on roof. Maybe a curved mount on canoes hull!!
Light canoes stay on roof when popping up.
attachicon.gif
IMG_0785.jpg
Click to expand...
adding the 2nd battery will sure help when the sun doesn't co-operate. Takes a long time to recharge two big batteries though!
 
buckland said:
Great detail I need to know. Thanks Lars. To expand my capacity for four days of rain I am thinking of adding my newly reborn DIY LiFePo4 battery in parallel. I have a good BMS but need to know if it is okay to do this with a Battleborn (in parallel)... does the BMS of the dyi need to match the specs in the Battleborn? Any possible snafus?
Click to expand...
Agreed, great detail! I'm curious about this question too.... two different BMS's.... I would guess no issue, but.... would love to here rando's input!
 
There shouldn't be an issue with DIY battery in parallel, even with a different BMS.

In an ideal world, the BMS never has to do anything because the charge parameters are all within the BMS limits and the cells are balanced.
 
A footnote and question. I did find a few loose solder on a few cells on my dyi. Since then it sits at 13.3 or 13.4 daily so I have decided to add it to the camper. I have been making a new battery box for it and have the Renogy 1000 W inverter (to charge the ebike battery) in a cubby beneath the battery box (with vent holes).
As I will be putting these two batteries (Battleborn) in parallel I thought I would dedicate the Dyi battery as the charging one. So I believe I need a switch to keep both in parallel to solar charge but a switch that separates them for use of the inverter. Does anyone suggest a switch that would be a simple mechanical “both or one’?
 
That switch looks robust and will fit in the battery box. This is probably a simple question (dumb)....
I have two batteries in parallel which most the time will remain as one. 200 amp unit. I want to run the inverter only off one when needed to charge ebike. For this purpose I’d run extra positive leads to the switch IN posts from each battery and a positive lead from the inverter to the OUT.
Does the inverter negative then go to the battery I dedicated for inverter?
 
the ground (-ve) of the system remains common to all batteries/systems.

Still wondering why you want to do this... are you wanting to ensure you don't drain the "reserve" battery? I can't see an e-bike charger doing that.
 
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