First build advice? Goal Zero Yeti 400 upgrades!

[BoJack]

Apologies for the long post. This is a collection of all my thoughts for the entire upgrade process…

I have a fun little project that I am hoping I can make work, but I am looking for some advice. The SLA battery in my older Goal Zero Yeti 400 has gone bad, but the rest of the unit works perfectly. I would like to replace the SLA battery with a DIY LiFePo battery. I know there are drop in replacement LiFePo batteries I can get that will give me the same 33 Ah, but I figured, why not build my own and see if I can squeeze a bit more capacity into the unit.

This will be my first LiFePo battery build, so I am starting with a smaller battery and have a set of goals to work toward to help keep the project moving forward. My 4 goals are broken down below. So far, this is the outline of what I am doing. I appreciate answers to any of the questions, but Goal #1 is where my focus is right now.


Goal #1: Replace the internal SLA battery with an 80Ah LiFePo4 DIY battery with BMS.

• • To achieve this goal, I just want the Yeti to function just like it always has with a new 80Ah LiFePo battery inside the original case.
  • I have found some 80Ah EVE cells that, according to my mock up, should fit in the space I have, leaving me some extra room for a BMS.
    • These are the cells I want to use: EVE 80Ah LiFePo Cells
    • They seem a little expensive for the amount of power I get, but the trade off is they should fit inside the original case of the Yeti.
  • This is the BMS I am considering: eBay Link
    • I plan on running it in the 60A common configuration.
    • The specs say it will be of an appropriate size for the limited space I have.
    • States that it has active cell balancing.
    • I do not plan on pulling anywhere near 60A from the battery at any given time (unless running the AC inverter at the full 300W). Probably 10A at most at any given time. (Everything else in the Yeti is limited to 10A and I am ok with that.)
    • Should be powerful enough to allow me to add external charging down the road (Goal 4) to get faster charging from solar than the 120W PWM built into the Yeti.
    • I am also considering the Daly 60A and Daly 40A BMS. Both of these would be a little harder to fit my space restrictions, but if one is a better BMS, maybe it is worth the effort.
• Questions I have about this stage:
  • 1.1 - Will the circuitry of the Yeti be able to charge/discharge the LiFePo battery correctly through the BMS? Essentially, will the Yeti think it has an SLA battery installed and charge/discharge it correctly? My understanding is that the BMS manages the cells and makes the group look like a standard 12V battery to whatever it is connected to.
  • 1.2 - Does anyone have any knowledge/experience with this BMS? Is it safe and will it perform like I expect it to? (Active Balancing, have enough overhead for the Amp draw and future charging upgrade.) Will it last?
  • 1.3 - The BMS says continuous discharge current is 80-100A. I plan only only drawing around 10A. Is this a problem for my application?
  • 1.4 - For the size, the specs seem impressive. If you have experience with this BMS, are the dimensions correct? (42 x 60 x 7.4mm)

Goal #2: Later, I want to add regulation to the 12V output.

• • To achieve this goal, I want to be able to make the 12V outputs regulated and able to support 10A max.
  • This will mostly be for running my 12V fridge and some 12V lights/accessories.
  • I will probably have the 12V car port and the barrel connectors regulated together and sharing the 10A. (They are currently all wired together.)
  • I have not settled on a regulator yet. Open to suggestions.
    • I would like it to fit inside the case with little modification if necessary.
    • Highest efficiency I can get would be nice.
    • I can potentially add another fan and temperature activated controller to help with cooling during high draw if necessary.
  • I can be flexible on having this mounted inside the case. The ones I have seen look pretty large. If the side of the case needed to be modified so it can peek through or if it needs to be completely external are both options that are still on the table.
• Questions I have about this stage:
  • 2.1 - Does anyone have any recommendations for a compact 12V buck-boost regulator that can handle 10A?
    • I am going with 10A because my 12V fridge has a max Amp spec of 6A. This leaves a little bit of room for other accessories to run.
  • 2.2 - Would I be better off going with two smaller regulators, one for the 12V car port and one for the 12V barrel ports?
  • 2.3 - It is NOT a good idea to get two smaller regulators and parallel their outputs to get my 10A, right?

Goal #3: I want to be able to use the Anderson Power Pole connectors on the side of the Yeti to expand capacity.

• • To achieve this goal, I want to be able to build an identical 80Ah battery (or two) that I can connect externally to the Yeti.
  • The Yeti 400 was designed to add 4 additional 33Ah SLA batteries, giving it 2000Wh of power. Two batteries on each APP connector, one on the left and one on the right.
  • The APP connectors connect the batteries in parallel.
• Questions I have about this stage:
  • 3.1 - Can I parallel 2 or 3 80Ah LiFePo DIY batteries together safely? What should I look out for?
  • 3.2a - My understanding is that the batteries will have to be at the same state of charge when connected. Is there a way around this?
  • 3.2b - Will the two BMS’ be able to “equalize” the charge if connected together in parallel and left to sit?
  • 3.2c - Is there a better way than paralleling another identical DIY battery?

Goal #4: I want to be able to use the second set of Anderson Power Pole connectors to add external solar charging for faster solar recharge rates when desired.

• • To achieve this goal, I want to be able to use an external MPPT charge controller connected to the APP connector on the side of the Yeti and charge the battery/batteries.
  • The Yeti spec sheet says that these APP connections can support 12V, up to 33A, 400W max.
  • Looking inside the unit, I can see that the APP connectors connect directly to the battery and there is a 60A fuse installed on the positive lead.
  • Wanting to go with a high quality MPPT charge controller to handle 300-400W of solar charging.
  • I don’t fully understand the relationship between solar panels and charge controllers just yet, so I made this the last goal.
• Questions I have about this stage:
  • 4.1 - Is a Victron SmartBlue charge controller the way to go? Suggestions welcome.
  • 4.2 - Can the external and internal charge controllers safely be used simultaneously to charge the battery?

This is mostly an experiment. A tool to learn more about solar power, LiFePo batteries and how to build them. It all seems reasonable to me, but I have a limited understanding. In the end, is this even possible? Will it work like I hope, or is it just a pipe dream? What kinds of things have I not considered? What are the major pitfalls to look out for? I am hoping to get some advice before spending money I will later regret. Thanks for reading and for any advice you have. It is greatly appreciated!​

 

[NVS]

The biggest problem is it will not charge the lifepo4 battery correctly because it is set to charge sla battery. Same with the built in charge controller. I would either replace the sla battery, or I would make it connect to a external true deep cycle to give it more capacity.

Then I would build a toolbox solar generator with lifepo4 and all the correct components. Tons of YouTube videos on it.

 

[BoJack]

Hmm... bummer. So, is there something special about a “drop in replacement” LiFePo battery?
I am assuming that this means that the charge controller does not get to a high enough voltage to top off the LiFePo battery?
I had considered building a solar generator from scratch, but though it would be way cooler if I could re-purpose the Yeti to do the job.

 

[NVS]

I don't no why they say drop in because there is no way they can get fully charged. There should be a charge spec. On the battery. I just went through all of this with my motorhome lithium install. Plus I've been playing around with old ups battery backup trying to put lithium in it. You have to have a DC-DC charger to get the voltage right. But even that doesn't work because current won't flow both ways it will only charge.

 

[BoJack]

So, a BMS doesn’t have a built in boost converter to ramp up the voltage to the appropriate level if it comes in a bit to low?
Could you not have 2 sets of leads coming off your BMS? One that connects to the DC-DC charger and then one set that goes to your load? Maybe out to a buck converter if the lithium voltage is too high for your application? Then the DC-DC charger could charge and the buck converter could power your load…? Or, am I totally wrong here?

 

[DerpsyDoodler]

So, a BMS doesn’t have a built in boost converter to ramp up the voltage to the appropriate level if it comes in a bit to low?

no

 

[BoJack]

no

Well, it looks like there is still a lot to learn…

 

[DerpsyDoodler]

Think of it like this. a BMS is a protection device for your battery. Nothing more, nothing less.

 

[BoJack]

I guess I was figuring with all these lead acid “drop in” replacement lithium batteries out there that they were doing something with the BMS to make it work with all the lead acid battery chargers and stuff to make the lithium battery appear and act like a regular old battery. I’m no engineer, but it seems like this would be a thing that could possibly be done…

Anyway, I have pretty much abandoned this iteration of this project and am now looking at either building my own battery from prismatic cells, or just getting a completed battery and building my power source. I go back and forth on what I should do. I feel like I could get a smaller system if I built my own battery, and once the battery is assembled, it is the same as buying one. Being this is my first foray, I have a hard time deciding what to do. ?‍

 

[Daedalus]

as a fellow GZ yeti 400 owner i had looked at the LiFePo drop in path, mainly through laziness as i have other mods underway with the unit (Laptop port from sherpa 50 and QI wireless charging. I hadnt helavily looked into a DIY cell build. The main concern is how the LiFePo cell will be charged by what the unit thinks is there. it will obviously be DC voltage, 14 volts i recall. The longevity of the liFePo is a concern. A chap on youtube did a Bioenno LiFePo drop in upgrade to a smaller 150 AGM yeti. it seemed to work ok, but ive not seen any further videos on its update.