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Thread: Yet Another Converter Question
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05-11-2023, 04:47 PM #11
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My brand new 2022 Imagine 2400bh came with the standard 8955 converter. Even with the standard 165W Furrion solar system I was disappointed that GD was not installing the converter cable of properly charging LiFePo batteries. I called WFCO and they were very friendly and told me about the model where it was supposed to auto detect and explained the process for it to auto-detect and if you ever switched back to Lead Acid to call them and they would guide me how to get it to switch back. They also decribed the other model where it was just a switch on the board to toggle between LiFePo. I liked that idea much better than having to rely and trust the auto-detect feature so I bought their model "WFCO WF-8955LIS-MBA" since I still had the Lead Acid battery installed and am switching over to Big Battery Razors (LiFePo) in the next week or so.
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05-11-2023, 04:56 PM #12
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This is a pretty simple system. The battery and converter are in parallel which means they share the load. A slightly higher voltage at the converter output ensures that it is the primary power source when connected to shore power. The down side to this is that the converter really has no idea of the state of charge of the battery. It only sees the total load. Meaning it cannot differentiate between house load and battery charge load. Here is a scenario that is common with me and I think with many RVers...
Suppose you're on shore power for a few months. When it's time to move, you run the jacks and do all your stuff while still plugged in. Then you hook up to the truck, drive for a whole and then set up at the next place also while plugged in. Maybe after all this the battery is down 5 amp hours (95% SOC) for a typical group 27 wet cell.
The converter goes into bulk charge mode for 4 hours because during setup the house loads never went below the undisclosed current threshold. Then the converter goes into absorption mode because, again, the house loads never went below the undisclosed current threshold. Finally, after 44 hours the converter drops down to float mode. Any change in current will cause the converter to return to absorption mode. All of this comes from the WFCO website. This whole process has overcharged and in my experience damaged or destroyed too many wet cell batteries. That's one reason I went with lithium.
Not being an electrical engineer, I see two solutions. One option would be to install a shunt that measures battery current only. Then the converter could set voltage based on battery condition. In that scenario, the converter would function as a true smart battery charger and the house loads would likely not be affected by the varying voltage (between 13.2 and 14.4 volts). I have not found a converter that would do this.
Another option would be a switch. In my case (and I think most others) all I need the battery for is to operate the jacks and as a UPS for refrigerator and climate controls. If the battery could be switched out of daily operation, it could be charged by a separate smart charger.
Rant over.... any suggestions?
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05-11-2023, 08:08 PM #13
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Just as a bit of info, I have a MeanWell NPB-750-12 and the efficiency rating is listed at 92%. Every manufacturer's product is different, but there are some that are more efficient than others. The MeanWell NPB also is not a time base unit, it goes by tail current (10%) for switching to float mode.
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05-12-2023, 04:46 AM #14
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05-12-2023, 09:52 AM #15
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Not exactly. When I was doing research on getting a LFP charger/converter (CC) for my homemade built LFP battery, I looked at a lot of different available brands, and for me, the NPB was what I went with. That CC has dip switches on it that will allow you to put it into 4 different modes...FLA, AGM, LFP, and a custom mode that you can set the parameters to your own liking.....if you purchase the programmer.....I did not. So in looking at my best options for settings, I chose the FLA setting for my LFP battery. In FLA mode, 3 stages, the max output from it is 14.4V and float ends up at 13.4V. I was not and am still not a fan of taking LFP batteries to the full 14.6V that most manufacturers do with their LFP chargers. That is the MAX voltage that a LFP battery should ever be exposed to. In other words, I like to keep the voltage at some point UNDER the 14.6, to keep from the unneeded stress of the 14.6V setting......and running in FLA mode does just that.
On the MeanWell NPB, once it is powered on, it will look at the amount of current draw and if needed, it will go into Constant Current charging, then if there is not enough load or 12V stuff on the trailer powered up, it will drop to the 13.4 float level. Then you can turn on as many things as you have in the trailer that draws 12V current, and it stays at the 13.4 level. In order to get it to go back up to bulk charging level, it has to be cycled off, then back on. So for me, I make sure the battery is fully charged before traveling, and I run my 12V dual compressor fridge during the trip/driving time. On average, it will consume about 6 amps per hour. Then, when I get to the campsite (we almost never boondock), I will go ahead and unhook the trailer and do my auto level, then put the slides out. After that, I then plug into shore power and let the battery charge, although I could just turn the battery disconnect off (the one I added, not the OEM battery disconnect) once the battery is charged and just run on the 12V from the CC, I never do. With the NPB set to the Flooded Lead Acid mode, I don't have to worry about the battery being overcooked because the max voltage out of it is 14.4V and the LFP battery max is 14.6V. It's definitely NOT just turn everything on and let it go, but it's what I prefer and hopefully the "extra effort" will help preserve the LFP battery and make it last longer than if it sees 14.6 all the time.2016 F350 CrewCab Dually
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05-12-2023, 09:56 AM #16
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Any system that attempts to charge a battery while at the same time powering loads will be subject to this phenomenon. Without some kind of feedback system from the battery, there would be no way to truly identify the needs of the battery. This works to a certain extent when charging lead acid batteries because they prefer to remain at full charge - they even like a little bit of overcharging occasionally. By switching from constant current charging to constant voltage, a charger should be able to find the battery’s ‘sweet spot” and maintain that voltage. Since that voltage is still above the 12 volt threshold, a converter can also continue to supply sufficient power for the various loads.
As more and more people switch to lithium (something the RV industry is lagging behind on) better charging/monitoring systems are needed. Lithium is actually much more susceptible to damage caused by overcharging. The only reason they work in this situation is that the battery’s internal BMS acts like a regulator and controls the charge.
Below is a fantastic article that does a great job describing this. Think about a power tool (drill for example). That tool’s battery is either charging, resting, or discharging. The charger can fully evaluate the battery’s state of charge and react as needed. The battery in an RV (while operating on shore power) is not afforded that luxury. It can go from charging to discharging in an instant, and typically sits at a state of full charge while the charger continues to apply a charge. The solution is expensive- dedicated monitoring and separate charge/load circuits. A good BMS is, at least for now, the most financially viable option.
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05-12-2023, 03:37 PM #17
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I have to disagree. You are correct that every manufacturer uses a slightly different charge profile and yours is no exception. You have chosen a profile that works for you (and it works for me as well with my lithium battery)
My issue is that your converter/charger is not changing modes based on tail current. It is making that decision based on tail current plus house current. That combination will never be less than tail current. In your case (switching to float mode when tail current drops below 10% of batt capacity) that switch will occur when tail/house current drops below 10 amps (100 amp hour battery. ) If your house load is 11 amps (which is not hard to do), that switch will never occur. I didn't look that deeply into yours, but most chargers have a time limit on top of the primary current trigger to protect everything else from battery faults.
I do however like that once yours is in float mode, it takes a power cycle to get it back to bulk mode.
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05-12-2023, 03:58 PM #18
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It is not that difficult or expensive to remotely monitor battery current. I just found a 150 amp shunt from Newark Electronics for less than $20. And one would not need separate power devices for house and battery. A single power output device (most likely a transistor of some type) would function just fine if the control circuit was monitoring only the battery charging load.
The converter/charger is electrically located somewhere between the battery and dc distribution panel. In its simplest form, the battery and distribution panel are both connected to the positive lug of the converter. All one would need to do is measure the current on the battery wire only (external shunt). The way the converters are set up now, all the combined current is measured internally. For that matter, the split could be made internally with the shunt located inside the box. Then the box would have three lugs: (house, battery and combined ground.)
In that configuration, all of the decisions about voltage would be based on battery current only and not battery/house current. Then there would never be the instance in which house current was too high to allow the charger to switch to float mode.
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05-12-2023, 05:13 PM #19
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You missed the part where I said that I charge the battery first, before leaving on a trip. At that time, there is basically nothing in the camper drawing current from the 12V system. Also, tail current is not based off of battery capacity, it is based off of the total output capacity of the charger. In my case, the NPB is capable of 43 amps, so down to 4.3 amps will trigger float mode
2016 F350 CrewCab Dually
2018 Momentum 394M...Heavily Modded!
2023 Suzuki GSX-S1000 GT+
Excessive Payload is a Wonderful Thing
"If it ain't fast....It ain't Fun"
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05-12-2023, 05:53 PM #20
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