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Issues with SunGold Power 3000w 12v inverter. Low charging voltage. Opinions please.

FrankSquid

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Sungold claims that their inverter is compatible with Lifepo4 batteries SunGolds own documentation states that the Lithium charge profile is only 14.0 volts. LifePo4 batteries require 14.2-14.6 volts to charge to 100%. The inverter that I received won't even charge to 14v the display voltage is inaccurate and is actually outputting 13.6v according to my Renogy shunt and two separate testers. Sungold clams that this is acceptable because of a software limitation of the inverter. Now they are telling me to charge with SLA profile. I complained of the issue within a week of receiving the inverter and they refuse to acknowledge that there is an issue. I will need to buy a new system or charger or risk damaging my batteries?
 

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I took interest in your post, Frank, as I had similar concerns when I purchased a Sun Gold Power 4000W 24V split-phase LFP series inverter/charger for charging two Ampere Time 24V 100Ah LiFePO4 batteries. I also have received no constructive answers from Sungold support despite several emails. In the end, I had to answer my own questions. I learned a lot, but in the end I returned the Sungold for another. Although it’s been a while since you posted, maybe you and others can benefit from my experience…

Table 2.5.1 in the user manual shows a charging profile for the charger that's broken into phases: Bulk, Absorption, and Float.

The SunGold unit has an amber LED indicating "fast charge mode" and a green LED indicating "float charge mode". How these "modes" relate to the charging profile of Table 2.5.1 is not explained. I can only assume that "fast charge mode" corresponds to the Bulk and Absorption phases in the diagram, and the "float charge mode" corresponds to the Float phase. The user manual also says that when the charger enters the Absorption phase, the “fast charge mode” LED blinks.

The charging behavior that I've observed with my SunGold charger does not conform to this profile, and it led to a lot of confusion for me. The question is what is the charging profile of the Sungold inverter/charger with battery type set to 7 (LiFePO4)? I was able to answer that by taking measurements of battery voltage, amperage, and SOC (state of charge) using a battery monitor (Bogart Engineering’s Tri Metric TM-2030). The only control the user has over the charging characteristics of the SunGold is the setting of the battery type and the constant charge current (via the liner). The differences are left to the installer to figure out.

With battery type set to #7, I was able to get the SunGold to charge the LiFePO4 battery to 99+% SOC in Bulk phase before the amber LED starts blinking indicating that the Absorption phase has begun. The Absorption phase is very short (a few seconds) before the green LED, "float charge mode", is lit. The charging session ends when the battery voltage increases to the “fast charge voltage” of 28V (14V for a 12V battery). Virtually all charging is being done at less than 3.5V per cell. For a 12V battery that’s 3.5 x 4 = 14V.

The battery monitor indicates that the battery is 99% charged in float mode (two green LEDs lit), and the battery amperage is 0A. I verified that the battery is fully charged by disconnecting the battery from the SunGold and connecting a charger specifically designed to fully charge a 24V LiFePO4 battery. The Ampere Time 24VDC charger could only add 0.2Ah of additional charge into the battery. The battery was for all intents and purposes fully charged, without any Absorption phase.

Conclusions:
  1. Battery type #7 gives a “fast charge voltage” of 28V (14V for a 12V battery). This is not the charging voltage. It’s the voltage at which the charger switches to the constant voltage, i.e., Absorption phase if the battery is not yet at full charge. At this battery type setting, the battery will be fully charged in the constant current (Bulk) phase. There will be virtually no Absorption phase, and the charger output voltage will be set to the float voltage (27.6V -- 13.8V for a 12V battery).
  2. To produce an Absorption phase on the SunGold, the “fast charge voltage” must be lowered, for example by setting the battery type to #3 (Lithium) or #9 (Classic LFP) both of which have a lower fast charge voltage. The battery will be only partly charged when the fast charge voltage is reached.
  3. Setting the battery type to #4 (Sealed lead acid – 14.4V) will likely increase the charge current to the maximum that the SunGold can produce. For a 24V charger that’s 60A, double that for a 12V charger. The battery will be charged faster than battery type #7.
  4. There is no need for my LFP battery to be charged quickly, so I also turn down the constant charging current to MIN. The battery is still charged to full, but by extending the charging time less stress is put on the battery.
  5. Unfortunately, the SunGold battery charger can’t be programmed to cut off charging at, say, 80% SOC which would be nice to extend battery life. For example, if the SunGold is used to back up the utility grid, leaving the battery at 100% SOC for long periods of time will reduce a LiFePO4 battery’s Ah capacity. It might be better to use SLA batteries that need to be charged to 100%. Alternatively, one could pay a higher price for an inverter/charger with more user programming capability.

Note: Make sure that the cables to the battery can handle the charge/discharge amperage, and that any disconnect switch or breaker is not resisting the flow of current. Any significant resistance in the cables to the battery will prematurely halt the charging operation, leaving the battery under charged.

The reason I returned the unit was because there were unpredictable instances when the charger stopped charging the battery in the middle of the bulk charging phase, and, as I said, my experience with SunGold support was less than impressive. Getting connected to the engineering staff is all but impossible. The usual response from support is to ask for a video showing the problem. I get the sense that the intention is to shield engineering as much as possible from problems caused by incorrect system installation/configuration. Many of the questions and difficulties that customers have could be addressed with a better written user manual.

What I’ve just written is based on my own struggles getting the Sungold working to my satisfaction. My understanding of how this inverter/charger works is certainly not complete. I welcome comments or corrections to anything I’ve written.
 
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Wow, wish I had read this back then, I wouldn’t bought their batteries!
Thank you!
 

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