FNDC and SimpliPhi batteries

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Posts: 73
Joined: Fri Apr 16, 2010 2:49 pm
My RE system: 24 LG275, 275W panels, 2 FlexWare500, four VFX3648, series/parallel Quad system, two FlexMax80, X240 transformer, MATE3, FN-DC, 6 SimpliPhi 48V 3.5kWh Lithium Ferro Phosphate (LFP) batteries, Cummins Onan 20GGMA generator (20 kW, LP Vapor fueled), OpticsRe.
Note: 12 Surrette Rolls 4Ks25P Batteries ( 4V, 1350 AmpHr), were replaced by the 6 LFP on June 21/19.
Location: Todos Santos, Baja California Sur, Mexico

FNDC and SimpliPhi batteries

Post by Mauricio » Fri Jul 12, 2019 8:25 am

On June 21/2019, I have retired my old Rolls 4KS25 and replaced them with 6 new SimpliPhi 48V 3.5 kWh, Lithium Ferro Phosphate (LFP) batteries. The transition went smoothly, and thanks to Outback/SimpliPhi integration guide, denoting all the required settings for Inverter, Charger, Charge Controller, FLEXnetDC and MATE3, the new batteries are performing very well.
My issue is with FNDC. While I think the unit is working properly and as intended by its designers, I believe that FNDC as it is now, it is not "tuned" for these type of batteries.
Compared to the Rolls, the voltage discharge cycle for the PHI 3.5 is very flat and lingers above the 50 Volts until the sudden drop at 49.5 Volts, so, SOC% from the FNDC and Battery Voltage do not agree with battery status I would have to increase the battery capacity setting 100 folds to have the two measures agreeing with each other. Not a solution.
Here is a real condition: From sunset to next sunrise, 13 hours, I consume about 12 kWh (real consumption), FNDC indicates SOC at about 79%, a bit low, but close enough considering my setting for battery capacity (Please note that FNDC was set with fully charged battery), but real battery voltage is still measuring 53.2 Volts. As per SimpliPhi technical support: ÔÇ£Anything over 53V is roughly a fully charged batteryÔÇØ.
So, after burning 12 kWh, I find myself still, with a set of fully charged battery. Free power? No, I think that since at sunset my battery voltage measured 54.5 Volts, the 1.3 Volts drop explains the consumption. Operating at such high levels of SOC, this discrepancy is not a real concern, the problem will be when, in need of more battery power (days of bad weather), recognize when the time has come to start that generator.
Comments from users that have also install these type of batteries will be greatly appreciated. Thank you, Mauricio.
Mauricio - Todos Santos, BCS

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Posts: 222
Joined: Thu Dec 21, 2017 11:39 am
My RE system: Outback: off-grid
- 1 GS8048A, Mate3, FlexNetDC, Hub10.3
- 2 FLEXmax 80
- 24 (8x3) 300w panels (7200w total)
- 6 SimpliPhi 3.4 kWh LI batteries (400ah , 20kWh)
- 1 Honda 3000 generator + one spare
Location: Wainiha, Kauai, HI

Re: FNDC and SimpliPhi batteries

Post by gtarolli » Thu Aug 15, 2019 8:34 am

Welcome to the group of (hopefully happy) Simpliphi owners. I started off with 3 batteries and now have 6, so approx 20 kWh. I am very happy with them so far. I find the SOC reported by FNDC pretty accurate as it is based on amp hours, not voltage. As you state, the voltage is hard, but not impossible to correlate to SOC. If you had lead acid batteries, it is probably hard to forget about voltage and pretty much ignore it. At least until it gets low like < 50.5v and starts dropping really fast.

Here's my observations and settings. I absorb at 56v for 6 minutes and then float at 54v. I find the temp. compensation gets in the way, so I use the limited setting at 54 and 56v and then fudge the charge controller absorb and float voltages to 56.4v and 53.5v. The temp comp limit keeps the target voltages within [54,56]. Without this I find that sometimes the temp comp messes with the target voltage which isn’t necessary in the 50-90 degree F range with LiFP.

After the PV stops outputting , my voltage drops to around 53.5v with a small load, e.g. 300-500 watts. The voltage drops down to 52.5v at about 50% SOC. Remember the Simpliphi chart is under a C/2 load or 10kw load for 6 batteries! I find that if I turn on a toaster and microwave, creating a 2000 to 3000 watt load I can lower my battery voltage by .5v to .8v, so I believe their chart is fairly accurate. Regardless, the voltage drop is so minimal and load sensitive that I pretty much ignore it and focus on amp hours which is what SOC reports. It is important to have the charge factor set right for FNDC, I use 96%.

I am curious what you have you battery capacity set to, I have mine set to 400ah. If you used say 12kwh overnight out of a total of 20, you should have been around 40% SOC with 8 kWh remaining, not 79% which is way too high, or maybe you meant 79% depleted and 21% remaining? We have a 7200 PV array and usually the batteries reach 100% and then drop to about 50% overnight. Once in a while with bad weather the SOC drops to 20% and the voltage seems reasonable per the chart (again with a small load). I only run my generator a few hours every few months. We average 12-20 kWh per day , it used to be a lot less but now we are spoiled with more panels, lots of sun, and great batteries.

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