Solar Controller

[Knotty-TMO]

My TM has a Go Power 30A PMW controller. Though it claims compatibility with LiFePO4 batteries, it seems very basic, relying on the BMS of the battery. I'd like to replace it with a more efficient MPPT controller. Anyone know of a good one that would fit in the same space? Most look too big and I'd have to mount it elsewhere and cover the opening with a blank and control it with a Bluetooth module.

Being in the northeast, trees usually make solar useless but controllers are relatively affordable and I like things to be right.

PS - I am upgrading to a PD4655 converter in the WFCO Panel and replacing my 100 Ah flooded batt with a 230 Ah LiFePO4.

 

[Bill-TMO]

What solar panels do you have? I'm not the expert, but I don't think an MPPT controller can do much with a single 12-volt input. It depends on using multiple panels in series to create an over-voltage. It then converts the excess voltage into additional charge current.

Bill

 

[Knotty-TMO]

What solar panels do you have? I'm not the expert, but I don't think an MPPT controller can do much with a single 12-volt input. It depends on using multiple panels in series to create an over-voltage. It then converts the excess voltage into additional charge current.

Bill

I just have the Go Power! Solar Flex 100W that came from the factory, so I won't get as much benefit from MPPT as if there were multiple panels. But, as I understand it, it will still improve efficiency about 18%. Per the excellent write up by rickst29, with multiple panels the improvement could be as much as 35%.

That said, my main reason for considering MPPT is to make sure the LiFePO4 battery doesn't get damaged. With only a single panel, maybe that's not an issue?

 

[rickst29]

I AM the expert.

Bill knows more than he admitted to, but I'l add some stuff.

The "Go Power!" website does not provide manual links via the home page menus, but I was offered a hidden link via a "chat" inquiry for support information, The manual for your model is at: https://s3-us-west-2.amazonaws.com/catsy.549/MAN_GP-PWM-30-SB.pdf

This older model provides a choice among 4 "battery profiles", none is a "user profile" with custom settings. (I attached the table of their built-in charge profile settings from that manual).

Their "Lithium" profile is two-stage. It offers 14.4 volts only 30 minutes per day, before falling to a "float" value of only 14.0 volts. 14.00 volts from the controller would be 3.500 at each battery terminal (over 99% SOC), but it might be insufficient to push high current through wiring and BMS into cells which are actually at lower SOC during the few great hours of the solar day.

A better "algorithm" for the SCC would be to simply offer all the power it has, with a higher voltage limit (either 14.2V or 14.4V) applied as a maximum value. With that in place, you use BMS "maximum charger voltage" to shut down incoming charge current when the SOC has reached the maximum which you want to have.

In storage, I like to keep my charge circuit open until my highest cell in each pack has reached about 3.25 volts (roughly 40% SOC). My maximum during trips is 3.45 volts (13.8 volts total), that's about 99.5% full.

In long term storage (e.g. winter), you should charge them up all the way (to 3.45V each) every 60-90 days to help with lifespan. When doing that, also that all the cells have been balanced really well (balancing should be invoked at a slightly lower voltage). Adfter the cells are all balanced, set the limit back down and allow phantom loads to pull the cells back down.

 

[rickst29]

Knotty - I have parts (brand new EVE-230 cells, a good BMS, and a compression assembly for a battery pack in my house. After buying the cells about 2 months ago, I decided to switch to a battery bank containing only EVE-280K V3 cells, so the old compression assembly is useless for me.

I CAN ship them a long distance via ground transport, and the shipping box for the cells i(the are new in original box) is marked for such shipping already - that's's how they were sent to my house. Interested? Send a PM.

 

[Knotty-TMO]

Great info. Thanks again rickst29.

 

[rickst29]

Here is a photo of that 'for sale" battery pack

Here is photo of that battery before doing cell replacement. Photo excludes the heater port cable (which I have and can send) and the final main cables "P-" and 12V+ (inside the TM, of course).

BMS is JK, a good one very high balancing current capabilty. 200A max continuous current.

Upon reassembly, one or more of the threaded steel compression rods can probably be shortened before I send it - the minimum length for each of those is slightly above the length needed to insert cells and spacers while the springs are uncomressed, allowing the second nut to placed on the rod without hassles.

Final installation will insulating sheets above and below the pack, so that any failure of the very thin cell does cannot create a short circuit between cells at different "-" ground potential values.

 

[Knotty-TMO]

That's cool. Never knew that the LFP cells needed all that compression!

Have watched some of Will Prowse's YouTubes but never got in deep enough to get involved with the forum.

 

[rickst29]

That's cool. Never knew that the LFP cells needed all that compression!

Have watched some of Will Prowse's YouTubes but never got in deep enough to get involved with the forum.

The most relevant thread within the forum (DIYSOLAR.COM) is around 40 pages long - and full bad guesses and irrelevant posts, - so don't go there

But the EVE specifications datasheets are all there too. The installation requirements echo the test procedure construction of a "clamp", and provide the required level of clamping force in NM. The specification for the newer LF280K-V3 cells is 3000 Newtons (minimum), 7000N maximum. Converting to "Pound-Force" at sea level, the minimum is about 675 pounds. CALB staff have told me that the want a similar amount of compression applied to their cells.

For smaller sized prismatic cells, you can use the value per square inch (that's about 16 PSI minimum) and mulptply by the size of the face to a get a total force value. The 230Ah cellls are less tall - IIRC the resulting value is slightly above 550 lbs.

 

[rickst29]

please feel free to call...

that allows quicker Q-and-A than posts. FYI and slightly off topic, I need to update my signature, showing that I'll be using this battery pack assembly from now on. Still work in progress, the double-wide remains narrow enough to fit into within the under-seat dining area storage area of my 2619.

840AH nominal (probably closer to 900 AH actual capacity). 12 compressed cells with 3 BMS units and 3 busbar sets acting as 3 parallel batteries within one compression "case".

I temporarily added bus bars( just for the picture, showing the cell layout.) Real assembly (within the TM) needs to also add ring terminals for BMS sense/balance connections at many of the terminals. Then the whole thing gets covered by a plastic safety sheet, before connecting installing the 3 BMS units above the sheet and making final connections.

Total compression (about 1400 lbs) need 700 lbs from 3 big springs down the center, with only 350 for each outside set. The big ones can handle up to 450 lbs each. The little ones I have there become fully compression and going not linear when pushed to fully compressed (around 135 lbs each). I have more "big ones", and might use them within the outside sets as well.

 

[Knotty-TMO]

Great stuff Rick. I called you yesterday and left a VM with my number.

 

[rickst29]

My review of the LiTime 230Ah battery pack

Thanks for the voicemail message!

I looked at the current LiTime offering for 230Ah, here: https://www.litime.com/products/12v-230ah-bluetooth-lithium-rv-battery?_pos=3&_fid=17513aa15&_ss=c , also reviewing the the "specifications" page here: https://www.litime.com/products/12v-230ah-bluetooth-lithium-rv-battery?_pos=3&_fid=17513aa15&_ss=c#specs_title

The price is very good, but the pack has no compression. The manual for the BMS is not available online, and some of their 'specification' current limit values are impossible for this battery pack to provide. Their warranty requires that their support personnel agree with the validity of any claim you make. In the case of a successful warranty claim, they reduce the amount of refund over a lifespan of 60 months (i.e. straight-line depreciated value remaining" at the time they claim is accepted.) There are lots of abuse exceptions within the warranty, but everyone has those.

Their battery packs are built from cells which are claimed to to match EVE capacity values. The one you pointed at is size 230ah, they also offer a 280ah pack. CALB does not offer cells in both of those sizes. I will, however, SWAG that they are not EVE cells, their are many OEM's building and selling "sdort-of-like-a-clone" sells in EVE product sizes vat lower cost.

The 230Ah battery pack weight corresponds to cells, bus bars, wiring, the plastic case, a bit of foam insualation holding the cells and BMS in place, and nothing else. It is waterproof. My assembly does not include an outer ABS shell, and it weighs much more - the compression plates (1/4" steel) are quite heavy, and I should probably cut and drill four more add-on L-bar segments before selling the pack, because even 1/4 steel bends under the stress of the compression bolts.

They show a photo of their BMS. That BMS is utterly incapable of surviving a 1000 amp "surge" for a full second. That specification is totally untrue. A BMS of this size is designed and built with a group of current-management transistors along the power path; they will absolutely positively BURN OUT if subjected to that kind of surge. The board planes and circuit "wiring" can't handle that either. Maybe it can handle about 350A for about 3 tenths of a second, but all of the 'magic smoke' will be released by the BMS if is subjected to a 'surge' either bigger or longer than my values. (BTW, I have been a consultant with a Chinese BMS company in the past, in exchange for freebies and kudos.)

In my mind, that impossible performance claim should put all non-experts in a state of doubt regarding their other performance limits, but I think that some are actually good - if used with additional limitations their did not describe.

EVE 230ah cells can deliver 230A continuous output current (1.0C) under standard temperature conditions if SOC is above 40%, but that load must be severely reduced when SOC has fallen below 30%. There are also temperature adjustments for that curve of allowed values, but they are not sever'e as the low SOC limit. Without posting the entire graph, I wil summarize it as "DONT PULL MORE THAN 0.2 FROM A 1.0C-RATED LITHIUM CELL AFTER CELL SOC HAS FALLEN TO 25% SOC. Within the downward range of 40% to 25% your load limit should be dropped to maybe .5C right away, then .25C at 30%. I don't know of a BMS which can do this in a dynamic way, just be careful with it.

Their "recommended charging current" of only 46A (0.2C) is lazy and wrong, it is only a somewhat convenient expression of complicated rules. SOC and temperature are both issues (again), but they flip in importance -- temperature below 40F (about 5C) is the primary concern, and SOC is less critical.

At low SOC and low temperature, you need to take extra care (because both factors impose big reductions, and they multiply togwether). The BMS can provide only an on/off switch based on temperature. When cells are near freezing, the ability of cells to accept charging is severely limited. The LiTime BMS recovery temperature is OK, but the cut-off temp value (0C) is much too low. It might be a configurable parameter, but LiTime doesn't offer the manual for BMS bluetooth app online. (GRRR, GERR, CUSS CUSS)

If all the cells in a battery pack are still below the max charge limit and the balancing enable voltage, their BMS will allow 'max current' into the pack until the pack temperature probes read 0C (freezing) .Charging must be stopped higher than that, a value should be set just slightly below the 'charge recovery' setting to prevent rapid cycling of the charge circuit state (enabled versus disabled). I personally use values of 6C 'recovery' and 4C 'disable'. Those are roughly 39F shutoff and 45 resume. 45F resume wastes some charging power on 'extra' heating when the packs have gone cold, but the 2C margin is needed to prevent rapid cycling of charge versus heater BMS operating state.

Their BMS doesn't provide a built-in heater control circuit, mine does -- with the limitation that it turns on and off according to the 'charge enabled 'state, it has no parameters for starting early and supporting both jobs at the same time. I use mine with 12v motorcycle seat heatedr pads, and I do have spare which I can send to the buyer of the battery pack.

Their lifespan specifications are totally bogus, uncompressed prismatic cells will NOT provide that number of cycles, and the time which will pass before reaching 4000 cycles (10+ years) or 6000 cycles (15+_years of daily charge/discharge cycles) is also unreachable with uncompressed cells.

 

[Knotty-TMO]

Here's a pretty good video by HOBOTECH about the Li Time 230 Ah batt.