diy solar

diy solar

Hi there! Been dabbling in solar for a while, but making the move to LiPo

kalisiak

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May 20, 2022
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13
Hello!

I'm new to the site, but have been dabbling in various solar DIY projects over the last 15-20 years. I currently have a 135W panel charging a couple of SLAs via a Renogy Wanderer 10A, which I use for LED lighting and USB webcams for a feral cat shelter that I built a couple years ago.

What I'm looking to do next is use a pair of Astronergy 360W panels with a Renogy Rover 20A Li to charge a 6S16P BMS-based pack that I built. The 18650 LiPo cells have been harvested from laptop battery packs, and the 96 batteries that I selected for this project are all able to maintain a decent charge. They're going to be housed in a locking, heavy, steel ammo box in case something bad happens.

What I'm struggling with is the user-defined parameters for the Renogy Rover. I have the Bluetooth module, so I can program the parameters, but I'm not sure if what I have come up with is correct?

I understand that bulk charge is constant current, equalize/boost is constant voltage, there is no equalization/float in Lithium, and no boost duration either.

LiPo batteries are constant current until it gets to 4.2V, then constant voltage until the current drops off to 0.

Sounds like Boost voltage is 4.2V then, but I'm not sure what a cutoff would be...

High Voltage Disconnect Definitely 25.2V
Equalization Voltage Appears to be N/A, because it's not lead, but I think the app requires a value for user-defined, so I'm not sure what to enter.
Boost Voltage I don't know what to do with this one?
Float Voltage Appears to be N/A, because it's not lead, same thing about requiring a value
Boost Return Voltage I don't know what to do with this one?
Low Voltage Reconnect Looks like 18.6V?
Under Voltage Warning Probably 18.3V?
Low Voltage Disconnect Definitely 18V
Discharging Limit Voltage I guess 15V?
Equalization Duration Appears to be N/A, because it's not lead, as above
Boost Duration Appears to be N/A, because it's not lead, as above

Any suggestions would be appreciated!

Thank you,
Chris
 
Hello!

I'm new to the site, but have been dabbling in various solar DIY projects over the last 15-20 years. I currently have a 135W panel charging a couple of SLAs via a Renogy Wanderer 10A, which I use for LED lighting and USB webcams for a feral cat shelter that I built a couple years ago.

What I'm looking to do next is use a pair of Astronergy 360W panels with a Renogy Rover 20A Li to charge a 6S16P BMS-based pack that I built. The 18650 LiPo cells have been harvested from laptop battery packs, and the 96 batteries that I selected for this project are all able to maintain a decent charge. They're going to be housed in a locking, heavy, steel ammo box in case something bad happens.

Why not 7S? Far more useful for 24V systems.

also consider that NCA chemistry is not famous for cycle life. You should consider operating them between about 20-80% SoC equating to 3.5-4.05V, respectively.

What I'm struggling with is the user-defined parameters for the Renogy Rover. I have the Bluetooth module, so I can program the parameters, but I'm not sure if what I have come up with is correct?

I understand that bulk charge is constant current, equalize/boost is constant voltage, there is no equalization/float in Lithium, and no boost duration either.

LiPo batteries are constant current until it gets to 4.2V, then constant voltage until the current drops off to 0.

Sounds like Boost voltage is 4.2V then, but I'm not sure what a cutoff would be...

bulk = boost = absorption in terms of the voltage. When you see these words in manuals, they are all referring to the same voltage.

High Voltage Disconnect Definitely 25.2V
Equalization Voltage Appears to be N/A, because it's not lead, but I think the app requires a value for user-defined, so I'm not sure what to enter.

Same as boost.

Boost Voltage I don't know what to do with this one?

Cell peak charge voltage * 6

Float Voltage Appears to be N/A, because it's not lead, same thing about requiring a value

With solar, you need a float to force your system to power loads with solar. Set float to Boost - 0.2V

Boost Return Voltage I don't know what to do with this one?

If voltage drops to X, restart charging in the boost phase.

Low Voltage Reconnect Looks like 18.6V?

3.6 * 6 = 21.6V

Under Voltage Warning Probably 18.3V?

3.7 * 6 = 22.2

Low Voltage Disconnect Definitely 18V

3.5 * 6 = 21V

Discharging Limit Voltage I guess 15V?

3.5 * 6 = 21V

Equalization Duration Appears to be N/A, because it's not lead, as above

yep.

Boost Duration Appears to be N/A, because it's not lead, as above

Nope. This is your absorption time, i.e., the CV charge time. Start with 15 minutes and adjust as needed. Check your cell specs and determine what the tail current is, i.e., when are they fully charged at 4.2V. You indicated 0A, but that's not necessarily the case. LFP is fully charged at 3.65V @ 0.05C (5A for a 100ah cell). In that case, you would want to set the boost time down to whatever it takes to drop to 5A.
 
Thanks for the feedback!

I don't remember why I decided on 6S, I think it just seemed reasonable at the time, based on the loads that I was originally planning -- I was going to use this kit last year to power a bunch of Peltier coolers to turn an antique ice box into a refrigerator. I built everything up as 6S16P with the BMS, and got that working with a bench supply, but never figured out the charge parameters, so I let it go.

We sort of gave up on the idea of the ice box (but we might still use it as a party trick with some pre-cooled beer and a 7lb bag of ice), and I'd like to use the gear as a DIY UPS to power some micro-electronics and LED lights in the barn. I could buy yet another BMS and another set of the hard-point 18650 trays, to make it ~7S14P.

And thanks for the responses on the parameters, that does make sense. If I reconfigure the cell pack, I'll give those a try.

Chris
 
Hopefully they are not really Lithium Polymer (Lipo) which are typically pouch cells used by RC helicopters and other RC hobbies to. They are very volatile.
 
By the same token, if these cells will be underdriven anyway, and used to power ~50-60W worth of electronics via https://www.amazon.com/gp/product/B08318HXL3, I might be better off just going with 8S and then buck it down to 24V? The solar panels are 39V Vmp, so 8*4.05=32.4V would be closer to the native power of the panels, so there would be less loss.

I don't recall what voltage ranges the Renogy supports, but I do know that you divide the voltages in half when programming for a 24V system. I'll have to take a closer look before I make any decisions.

Thanks,
Chris
 
Hopefully they are not really Lithium Polymer (Lipo) which are typically pouch cells used by RC helicopters and other RC hobbies to. They are very volatile.
Yes, they are LiPo 18650's. I tore apart a bunch of retired laptop battery packs, graded the cells, and reserved 96 of the best ones with the intention of going to 6S16P. (If I move to 8S, I'll probably switch to 8S12P.) I'll be housing them in a heavy-gauge locking ammo box with an inch or so of concrete in the bottom, a grommeted hole just large enough to allow the 12GA wire through, and they will be BMS-managed.

Chris
 
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Yes, they are LiPo 18650's.
If they are truly Lithium Polymer you should research what the RC guys do for safety. They do not store them at full charge and when charging them in the field they use asbestos bags to put them in so when they catch fire not too much damage happens to surrounding things.
 
with the intention of going to 6S16P. (If I move to 8S, I'll probably switch to 8S12P.)
There is a reason that many Lipo, NCA, and NMC packs get configured as 7S because that puts the voltage within the typical range of most 24 volt equipment. 7S BMSs are fairly common. I used NMC cells from Nissan Leafs in a 12P14S configuration for a 48 volt inverter before I switched to LFP.
I am also not sure why you want make the pack voltage closer to the solar panel voltage? Typically the charge controllers need some headroom. They also use a buck converter so adding another one from the battery to the inverter is actually increasing losses.
 
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If they are truly Lithium Polymer you should research what the RC guys do for safety. They do not store them at full charge and when charging them in the field they use asbestos bags to put them in so when they catch fire not too much damage happens to surrounding things.
When I broke the pack down last fall, I depleted the cells down to about 3.7V. I don't trust nickel strips with a melange of cells, and instead use spring terminal cell trays with a 12GA bus bar, so I was able to pull all the individual cells out of the pack. They are stored in such a way that nothing can touch the terminals, to reduce the risk of anything happening during storage. I've got all of the handling details covered; I've seen the fires these things can cause. I'm just working through the charging parameters at this point, and, well, that and apparently adding one more S to what I've already bench tested.

Regarding 7S vs 8S, the initial thought was that since I would be underdriving the cells, I would want to make sure there's sufficient headroom to power the inverter. But I guess if I'm cutting off at 3.5V or thereabouts (maybe 3.4V, or 3.42V, if I can specify two decimal points, to give 24V), I should just stick with the suggested 7S, and have a voltage cut off circuit effectively set to the inverter's voltage, and that's what would kick back to AC. I'm likely going to need a buck on the output of the pack anyway, though, because I kinda doubt the inverter could handle 28V and change, but I did post a question, and hopefully they will respond.

Chris
 
since I would be underdriving the cells, I would want to make sure there's sufficient headroom to power the inverter. But I guess if I'm cutting off at 3.5V or thereabouts (maybe 3.4V, or 3.42V, i
Are you talking about the low voltage cutoff? The classical voltage for that type of cell is 3.5 on the low end and 4.1 on the high side. I do not know what you mean by "underdriving" the cells. Do you mean you will be pulling less Amps? The cells don't know or care. I ran my Nissan Leaf modules from 3.8 to 4.05 and rarely went into the lower part of that curve. Those voltages are where I had figured 80 percent of the capacity was. I picked a higher low end voltage just to avoid the lower knee of the discharge curve. That is essentially what @sunshine_eggo said earlier including a 7S pack.
 
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Seeing as how I didn't actually pay anything for these batteries, I was going to go with 3V and 4.2V. But I'll run with the other voltages that were suggested in this thread. I should have enough capacity to power the devices that I'm planning on powering, but I can leave room for expansion to add more cells if needed.

For anyone visiting this thread at a later date, keep in mind that you do have to be careful when dealing with "legacy" Lithium Ion aka LiPo batteries. Lead and Lithium Iron Phosphate LiFePo batteries are much safer, but that's not what's used in standard laptop battery packs like what I tore apart to pull the 18650's out of them. Regardless of whether it's a DIY solution or not, if you short Lithium Ion batteries, or just do something stupid to them, the whole pack can combust. When LiPo batteries burn, the cells themselves can reach 1000 degrees C. Aluminum melts at 660 degrees C, and different types of steels melt in the 1300-1600 degree range, so suffice it to say, combusting LiPo batteries are bad juju. Normal fire extinguishers don't work well to put out a lithium battery fire, and in some cases, the best you can do is wait until the fire burns itself out, and then you flood the cells with water. So, kids, be careful when working with LiPo batteries, and never try to charge LiPo batteries directly, always use a BMS, or Battery Management System.

Chris
 
but that's not what's used in standard laptop battery packs like what I tore apart to pull the 18650's out of them. Regardless of whether it's a DIY solution or not, if you short Lithium Ion batteries, or just do something stupid to them, the whole pack can combust. When LiPo batteries burn, the cells themselves can reach 1000 degrees C. Aluminum melts at 660 degrees C, and different types of steels melt in the 1300-1600 degree range, so suffice it to say, combusting LiPo batteries are bad juju. Normal fire extinguishers don't work well to put out a lithium battery fire, and in some cases, the best you can do is wait until the fire burns itself out, and then you flood the cells with water.
I think it is important to distinguish Lipo from other Lithium Ion chemistries. 18650 cells are a cylindrical cell of a certain dimension (form factor). The chemistry can be one of many Lithium Ion chemistries. The most prevalent is NCA or NMC which are what Tesla typically used in their early cars. Lipo is different.but can be found in 18650 form factor but mor typically in the pouch packs popular wit RC hobbyist for their light weight to power density.LFP or LiFePO4 can occasionally be found in 18650 form factor and is one of the safest Lithium Ion chemistries.
 
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