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alternator - Renogy dc/dc charger/mppt - 100 ah battery - Goal Zero 1500x

philos70

philos70

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Can I connect a 100ah LiFePo4 battery to the Goal Zero Yeti 1500x in parallel without needing anything but a fuse/cb between the two? I'm looking to double my battery capacity without getting rid of the GZ that came with my Scout camper. The GZ can handle 680 watts or 12 v and 50 amps input. I just got the Renogy charger/mppt and will use that regardless to keep the GZ charged with the alternator. I just want more battery capacity.
Do I need a way to step down the charging amperage from the the new 100 ah lithium battery to the goal zero? If so, how?

Or do I not understand what "charging in parallel" means? I've read manufacturers warning not to combine batteries from other sources. I've read DIY people who say as long as you go through x steps you'll be ok.

Thanks for any help offered...

Jeff...
 

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BATTERY DETAILS​


  • Cell chemistry: Li-ion NMC
  • Pack capacity: 1516Wh (10.8V, 140.4Ah)
  • Single Cell Equivalent Capacity: 421Ah @ 3.6V
  • Pack Lithium Content: 126g
  • Lifecycles: 500 Cycles to 80% capacity (Discharge rate: 1C, Full charge/discharge, Temp: 25C)
  • Shelf-life: Charge every 3-6 months
  • Management system: MPPT charge controller
 
First problem, your GZ is 10.8V NMC vs. 12.8V for LiFePO4. I wouldn't want to parallel those myself, but maybe if you connect to the GZ's internal MPPT controller it can perform some magic. MPPTs are really designed to work with solar panels, but they do perform voltage conversion so if you understand your unit well enough you can use it for other things.

I'd even be leery of connecting the Renogy and GZ without knowing a lot more about each unit. What Renogy model is it? And do you plan to connect to the GZ's MPPT input as I assume, or connect some other way?
 
Doggydogworld said:
First problem, your GZ is 10.8V NMC vs. 12.8V for LiFePO4. I wouldn't want to parallel those myself, but maybe if you connect to the GZ's internal MPPT controller it can perform some magic. MPPTs are really designed to work with solar panels, but they do perform voltage conversion so if you understand your unit well enough you can use it for other things.

I'd even be leery of connecting the Renogy and GZ without knowing a lot more about each unit. What Renogy model is it? And do you plan to connect to the GZ's MPPT input as I assume, or connect some other way?
Click to expand...
There is an excellent video that demonstrates how the Renogy unit can connect two LiFePo4 batteries, or an AGM for that matter. What I want to do is put the GZ downstream of the new camper battery.


I'm hoping that by plugging the new LiFePO4 battery into the GZ high input port (12-50 volt, 50 amp max or 600 watts), the GZ mppt controller between the port and its NMC battery will know what to do. I'm guessing that's the magic you refer to above.

Would the GZ mppt know the difference between a solar panel charging at 600 watts or a LiFePO4 battery?

I understand the difference between NMC and LFP lithium batteries now - https://www.licarco.com/news/lithium-ion-battery-cell-types-lfp-nmc-cells-explained

The different voltages - 3.6 for NMC and 3.2 for LFP - makes a difference. From a website, "If you connect batteries of different voltages in parallel, the battery with the higher voltage will charge the battery with the lower voltage. This can damage the battery with the lower voltage, so it is not recommended to do this."

AFter thinking about this I think the question narrows to, "will the GZ mppt controller accept the input of the LiFePO4 battery so that the GZ battery is not harmed?"

Thoughts of course are welcome.
 
philos70 said:
I'm hoping that by plugging the new LiFePO4 battery into the GZ high input port (12-50 volt, 50 amp max or 600 watts), the GZ mppt controller between the port and its NMC battery will know what to do.
Click to expand...
Seems reasonable. If you can watch it, at least initially with a clamp meter to check amps, i would think it will work.

philos70 said:
Would the GZ mppt know the difference between a solar panel charging at 600 watts or a LiFePO4 battery?
Click to expand...
I have not done this but many have doe this successfully. Not sure how to keep it from over discharging source battery...maybe it will cutoff at stated 12V low voltage range?
 
Someone from another forum just posted this.

________________________________________

if this works, you are effectively. proving the yeti link in vehicle mode is pointless. From what I see online, a minimum of 15v input is necessary to the MPPT controller of the Yeti. I'm not sure outputting from your Renogy controller to both the battery and Yeti will work. Once the battery is charged, the renogy will stop charging it. At that point no more power would feed to the Yeti as your battery wont be outputting enough voltage for the MPPT controller in the yeti.

This is why a controller is needed between the battery and the yeti, to give consistent and correct voltage.
______________________________________________________

How about a step up voltage converter?


The GZ MPPT would read 24 volts and 25 amps even if the source battery dropped to 10 volts.
 
philos70 said:
a minimum of 15v input is necessary to the MPPT controller of the Yeti.
Click to expand...
This makes good sense.
philos70 said:
This is why a controller is needed between the battery and the yeti, to give consistent and correct voltage.
Click to expand...
I'd give it a go with what you have. Maybe the MPPT will work with a 13 battery where it may not with 13V array.
 
philos70 said:
AFter thinking about this I think the question narrows to, "will the GZ mppt controller accept the input of the LiFePO4 battery so that the GZ battery is not harmed?"
Click to expand...
The GZ MPPT performs voltage conversion, so I don't think it will harm the internal NMC battery. The spec page I found says the MPPT input port accepts 14-50V, so it does seem you'd need to boost the the voltage from the Renogy/LiFePO4 circuit. But the 12-24V converter you linked tries to maintain a constant 24V output voltage. That will fight with the GZ MPPT, which tries to adjust line voltage to maximize power coming from the "solar panels". I don't know how that would turn out.

Your Renogy also uses an algorithm specific to the charging profile you set. If you set it to LiFePO4 it'll push high current until the battery reaches 13.4V or whatever, then it'll throttle back.

Three algorithms fighting each other doesn't sound like a good idea to me.

How do you plan to get power out of the GZ Yeti? It won't flow out through the MPPT port, there's an internal diode to prevent that. I presume you'll connect the GZ's 12V regulated output port to your RV's 12V panel? But that seems weird since you're feeding the GZ from the LiFePO4 connected to that same panel. It's not quite the same as shorting the input and output, but it still bothers me.

There's probably a way to set it all up so everything plays nicely together. I'm just not smart enough to figure it out. I'd be inclined to just manually switch from one battery to the other, or maybe set up relays to do the switching.
 
I'm not schooled enough to address your well-made points. I think I'll test the system to see if it works. The worst case scenario, which isn't bad actually, is just to put one wire to the GZ and one wire to the new battery from the output terminal on the Renogy with switches on both lines. That would be a bother because as you point out, the charging profile for the battery and GZ are likely to be different. So not only a couple switches, but I'd have to change the charging profile with the Renogy app with each switch.

The whole purpose of this exercise is to increase battery capacity and charge the new battery and GZ with the alternator. I could have just gotten what is called "a yetilink" which would have allowed me to charge the GZ, but I resent being forced to use proprietary materials, especially when they're outrageously expensive - $450. I got the camper new off a lot, a cancelled order, so I'm stuck with what it came with, including the GZ.

The GZ has a bunch of output ports, both 12 and 120 volts. There is no RV panel. The truck camper is pretty minimalist - Scout Kenai.
 
I highly doubt if the GZ actually allows paralelling on the outputs. Normaly, the output are in the discharge direction, the GZ doesn't expect 12V backfeeding into the output port.

It might be protected, but it might fry the unit as well. Also, you won't be able to charge using the 12V output, highly unlikely it allows backfeeding: It's just a boost converter to convert the 10.8V from the batteries to 12V.

Charging using the alternator is generally pretty low, about 8-10A. Also, this is using the cigarette plug, which, in many cars, are not suitable for providing these currents continue (will heat up or worse)

Using the MPPT to charge *might* work, but you do need to add some kind of current limiting, to prevent the MPPT drawing too much current while trying to archieve the MPPT point.

Bottomline: Use the GZ as intended, for small trips, hikes, and so on. For in a van, it has too many drawbacks and things you need to take into account to make it some kind of workable.

Charging at low amps and using it as a big powerbank is fine, for everything else just get a regular setup. (battery, charger, dcdc and so on, and not the GZ/Bluetti/Jackery things)
 
I certainly don't intend to use the output ports on the GZ to do anything other than to run accessories. Charging using the alternator to renogy mppt uses a 4 AWG cable and can be up to 50 amps. The cigarette plug is not used. Using the REnogy MPPT has been demonstrated to work charging a battery. The output on the Renogy MPPT/Charger is 8 AWG and plugs directly into the GZ high charge input, which accepts 14-50 volts and up to 50 amps, totalling no more than 600 watts.

 
What if you permanently hooked up the car charger from the LFP battery to the GZ. https://www.goalzero.com/products/yeti-12v-car-charging-cable
You would continuously transfer 120w from LFP to GZ adding 1200w of capacity over 10 hours. Then when alternator charging, you would get 40 amps (max) to LFP while still using 10 to charge the GZ. I would add a LVD between LFP and the GZ so you are not relying solely on the BMS.
 
kbeefy said:
How integrated is the GZ stuff into the camper? Maybe you can sell it and just scratch build a better system that is all designed to work together....
Click to expand...
I like that idea a lot. Yeti are only designed for occasional use, not daily cycling. And the internal MPPT/inverter/etc. is mostly dead weight. Meanwhile, Yeti resale value is pretty good so the sale proceeds could pay for a lot of extra LiFePO4.
 
I've considered that, and may do it. The camper is new and I'm going to give the GZ a chance. I'll test drive the scotched together system first...
 
@philos70 curious what you ended up doing.

I noticed your post about charging the yeti with a DC-DC charger instead of their module. I was also interested in that because then I could:
- combine solar and alternator into the DC-DC charger to charge the yeti via the 50v input
- use the charging module for an external YETI tank battery
 
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