Newbie alert simple question about Voc on PVs.

Hello brilliant minds,
I have been dabbling with solar, in particular building portable 24V packs. I have two 100 watt panels in series to give me the 24v. So far so good, I'm getting the full rated amperage from the panels (just shy of 6 amps) and they fill up my diffent packs no problem. I build lithum packs from Li-ion, Li(NiCoMn)02 and LifePo4 batteries. My solar charge controller handles the chemistries and my configurations out of the box (plus custom of course if you want).

I recently purchased some unused brand new high end luxury EV batteries that are 48V that can put out almost 2KW of engery. I got them dirt cheap and I'm kicking myself for not buying more (only got 3). They are sold out and gone for good.

So since these are 48V I purchased two more of the exact same solar panels to put them in series to so I charge up the 48V pack I'm building, and I'm also going to convert some of my LifePo4 packs to 48V.

Voc on the panels is 22.8V which in series (4x) gives me 91.2 Voc. (Per the specs on the on the panel)

I was looking over the manual for for the MPPT charge controller and it under the specs it has the "Max" PV voltage listed as 138 Voc - 150 VoC.

I know I well below that is that going to be a problem? Obvisouly 91.2 Voc is plenty for charging 48V systems. When I check the actual voltage right now with just the two panels I'm in the 36-40V range as per the charge controller. I should be good to go yeah?

Thanks I know dumb question. Sorry!

Yes you are good to go as long as you stay below the rated max voc.

cyberfed said:

I was looking over the manual for for the MPPT charge controller and it under the specs it has the "Max" PV voltage listed as 138 Voc - 150 VoC.

I know I well below that is that going to be a problem?

Click to expand...

Never a dumb question... there are only dumb answers!

So... as well as staying below the Max VoC limit, you will need to see what the start-up voltage of your controller is, as well as the range over which the MPPT will operate to see if they are compatible.

Awesome, much appreciated!

Cheers

A very important point is the mis-conception that a 12V panel produces 12V. It does not. The designation "12V" means that the panel can be used to charge a 12V battery with only simple electronics. In actuality, most "12V panels" actually output between 17 to 20V. This becomes very important when you are wiring the panels in series, where your measured voltage is likely to be 72V for a string of four.

This becomes very important in system design, especially for the electronics you purchase. Traditional low-budget PWM controllers just act as a fancy on/off switch, feeding raw solar voltage directly into the battery. The battery being a load, will drag the voltage down to what the battery wants. So, a "12V panel" putting out 18V will be dragged down to a charging voltage of ~13-14V.

This becomes very important when you are charging higher voltage banks. Just as a 12V battery wants to be charged at 14+volts, a 24V battery wants charging in the 29-30V range, and a 48V one at 55-60V. That means a series string putting out 48-49Vmp will never completely charge your battery.

The more expensive MPPT controllers change everything. They act as a transformer, converting high raw solar voltage down to the voltage the battery wants, converting the extra volts into extra charging amps. But, for the MPPT to work, it needs a bit of voltage "headroom" to do the transformation. That means for a MPPT controller to charge a 48V battery, you need a solar string putting out at least 70 something volts. MPPT is great when you have to put your panels some distance away from your batteries. I myself am running 120VDC solar ~ 130' from the array to the controller, with no detectable voltage drop.

Be warned though that MPPT is so great, that some companies are now marketing fake MPPT controllers. They say MPPT on the label, but are really only cheap PWM electronics inside. One telltale is weight. A controller with a shipping weight <1lb is likely to be fake. Another clue is the presence of USB ports on the front. If it's small, light, and has a USB, don't spend money on it!

Thank you at @MichaelK, and yes I totally agree with what you are saying. I'm not sure what prompted me to be worried that the 4 panels Voc in series thats is going to be 91.2 Voc would be an issue since the Max PV Voc per the manual is as stated above. I guess I just asked myself "well is there a minimum?" outside of the obvious being able to provide a full charge of 48V which is something like 54V I think. I haven't built out the pack yet so I haven't dug into the max/mins of the batteries. Though I do have them. I also use a high voltage disconnect and a low voltage disconnect (connected to my chargers/inverters respectfully as a backup safety in case the controller and BMS, doesn't stop charging the batteries, keeping in mind these are all portable packs (heavy as they may be!). So I never fully charge my lithium batteries to 100% I stay in the 80-85% range. When triggered automatically it kills charging. I do run a full charge full discharge once a month to keep the chemistry of the batteries happy, the Renogy MPTT does this as part of its profile. I have a boat load of solar charge controllers lol. For some of my super small pelican sized tiny cases that can hold 1KW I was trying to find a small controller that could fit in the box. However since this pack was li-ion and not Lifepo4 chemistry I couldn't find one for my life. I ended up aborting the whole one packaged deal and found a controller for that chemistry that works, but its your standard size MPTT sized charger. For all my LifePo4 setups I'm using a Renogy MPTT controller I bought from them direct. I know what you mean about the cheap Chinese knock off's, they are all clones practically of the same device some company came up with.

I don't want to open a can of worms here but I'm going to ask anyways....

So regarding Li-ion battery charging (see OP for the actual chemistry I'm talking about). I've heard you can do it with Renogy chargers, I've seen people doing it on youtube (some of the more legit guys not just some rando dude) using Renogy MPTT chargers. I've poured over the manuals of Renogy's chargers, none of the specify that chemisty, they give you the ability to do "custom lithium" but I'm pretty sure that means custom LifePo4. I will admit I started my jouney into batteries and charging with 18650's and 21700's (see chemistry in OP). So I understand how that charging profile works. I dont know how different the LifePo4 charging profile is and if a "custom" profile on my 30A (overkill) Renogy MPTT controller could be used by the li-ion batteries correctly.

I'm transitioning away from li-ion for Lifepo4 for many reasons if nothing else the sheer amount of engery I can store. But I do have 3 li-ion packs one is 1KW the other is 2KW in a 24V configuration (7S 10P). They are all BMS'd up. I'm using an Epever MQTT charger (Chinese...tad concerning) because it plainly states it supports the li-ion chemistry and even the 7S configuration. It IS heavy and has no USB ports. Wasn't cheap either. So far its working great, in fact its charging them to the voltage I want perfectly. Now since these are portable packs, I ONLY ever charge anything while I am home (working from home helps...) so I can keep an eye on things, my panels are about 25 feet away from the batteries and charger and I've thought about extending that. The battery packs always remain in the shade and never cross temps remotely concerning (I have a thermal imaging device).

So can I use the "custom" setting on my Renogy for li-ions? I trust them more, but again lots of youtubers I see running the Epever controllers without issue and the comments say some people have been at it for years without issue. That all being said I still would prefer a "brand name" to charge the li-ions. But I can't seem to find one that plainly states the chemistry is supported or if it does it doesn't support 7S for some reason, either 6S or 8S but not 7S. No idea why and these are still not "name" brands.

If someone out there knows of a respectable MPTT controller that will do 24V (ideally also 48V) for li-ion batteries (see OP for exact chemistry) in a 7S configuration I am all ears. Price not important. I started off with li-ions because when I was learning to program microcontrollers the kits came with one for use for motors and other devices, and I guess I just kept going that way. Then I heard Tesla uses them essentially so I thought ok, I'm game I wanna build small packs to power my microcontrollers, thats how the addiction started. But with time, reading, watching, asking, LifePo4 became the clear choice and I have ceased my li-ion purchases and I'm on the Lifepo4 wagon now. The power of some of these batteries are insane. I have some brand new Japanese cells I'm building into several packs (Lev60s) that can push upwards of 500A continuous. That's just mind blowing, not that I would ever need to or could imagine that would be good for them long term. They are safer, more powerful, and if you catch em at the right team a great price. I'm eager to get my first Lifepo4 pack up and running, simple setup 4x factory Renogy purchased 24V LifePo4's. I just been spending so much time putting the finishing touch on my li-ion setups that I started first I haven't gotten to get them rolled into production. Between all my packs I can power my house for a day (approx 20KW). This isn't meant to be a house replacement solution obviously but it would be awsome to be able to run some appliances and other items off free energy while other packs are recharing in the sun!

That brings up inverters which I know is a whole topic of its own. Right now I have a 24V Giandel 1200w and a 3000w inverter and a cheapo 300 watt inverter. Both are pure sine wave inverters and I used my oscilliscope to validate they are a nice clean wave. Not sure what to buy for a 48V system. I've read the wattage of the inverter can impact the batteries life if improperly sized? True/false? That's why I picked up the 300watt one, for now since packs are being built I'm using the 300 watt just incase using the larger ones would some how impact the batteries life even if they are not plugged into something pulling a lot of engery. I haven't even used the 3000w one at all yet. Probably need to do some googling and reading on that. Biggest thing I see powering around the house would be maybe the fridge and my office. Not sure what the fridge pulls wattage wise but my office area pulls about 200 watts (peak, usually drops down immediatly to a little over 100 watts) using one of those "kill-o-watt" meters you plug into the recepticle.

Thank you again for the info!
Cheers

cyberfed said:

I don't want to open a can of worms here but I'm going to ask anyways....

Click to expand...

cyberfed said:

lots and lots of stuff....

Click to expand...

I can't answer your questions (as I know nothing useful about 'other' chemistries, apart from the fact they can catch fire),

But... may I suggest, in order to get some replies that:-
a) you shorten those 5 further paragraphs and make the questions clearer and
b) start a new thread with a meaningful title that relates to those questions.

I'm not trying to be awkward, but I doubt many on here will have time to read that much detail in a thread about VoC which appears to have been answered by post #5. Hence, I don't think you'll attract anyone who knows about 'other' chemistries as the thread stands.

Your right @SeaGal I tend to be long winded and will post in a fresh/appropriate post.

Much appreciated!
Cheers.