Yet Another Converter Question

[Roll With The Changes]

There have been many threads about converter charge profiles and lots of good info about about how the system works, but I still have a nagging question that I haven't answered.

In its simplest form, how does the converter differentiate between charge current and house current?

It seems to me that if the converter only has one connection to the system, it can only see the total load. I ask this because I have ruined several batteries over the years because the converter never switches to float mode. I think this is because the current that the converter sees never drops below the threshold to switch. It can't see what the battery is doing. It only sees battery and house current combined.

What am I missing?

[A.Texas.Yankee]

There have been many threads about converter charge profiles and lots of good info about about how the system works, but I still have a nagging question that I haven't answered.

In its simplest form, how does the converter differentiate between charge current and house current?

It seems to me that if the converter only has one connection to the system, it can only see the total load. I ask this because I have ruined several batteries over the years because the converter never switches to float mode. I think this is because the current that the converter sees never drops below the threshold to switch. It can't see what the battery is doing. It only sees battery and house current combined.

What am I missing?

Converter doesn't read loads or currents, only voltages (at least most). It won't matter what loads you have on the system as the converter is supposed to switch modes based on voltages and time limits. One of the reasons some of these OEM converters burn up is that they really aren't that smart. You could always dedicate the converter to the battery, but you would put additional strain on battery while on shore power and probably wouldn't see any performance difference.

HTH

[jkwilson]

The converter doesn’t distinguish. Current is current and it doesn’t matter if it’s running a light, charging a battery or doing a little of both. The converter changes output voltage based on the current being drawn. No current being drawn and it sets at float voltage around 13.4V. A little current being drawn and it kicks the voltage up around 13.8V. More current being drawn and it kicks the output up around 14.5V. There are time limits applied to some of these settings to avoid overcharging the battery and to avoid constant switching.

Don’t try to make sense of what a WFCO manual says. It’s a step below gibberish when it comes to how they work. It actually says the converter output is 14.4V, but if you measure it you won’t measure 14.4V.

[Roll With The Changes]

The converter doesn’t distinguish. Current is current and it doesn’t matter if it’s running a light, charging a battery or doing a little of both. The converter changes output voltage based on the current being drawn. No current being drawn and it sets at float voltage around 13.4V. A little current being drawn and it kicks the voltage up around 13.8V. More current being drawn and it kicks the output up around 14.5V. There are time limits applied to some of these settings to avoid overcharging the battery and to avoid constant switching.

Don’t try to make sense of what a WFCO manual says. It’s a step below gibberish when it comes to how they work. It actually says the converter output is 14.4V, but if you measure it you won’t measure 14.4V.

Thanks for confirming my thought process. This comes up again for me because I think my wf9855 might be failing so it's time to pick a better replacement.

First the failing 9855... I was watching my PD EMS display and saw a line current that was too high for what was running at the time. I cycled a few breakers until I found that the converter was drawing 8 amps (AC). The battery was disconnected at the time and when I power cycled the converter it was only drawing 3 amps (AC) with the same dc house loads. That looked more reasonable to me for refrigerator control, antenna amplifier, a few lights, etc. That tells me the converter is beginning to fail. It also explains my electricity bills being higher than I would expect. Does that diagnosis make sense?

[Roll With The Changes]

The converter doesn’t distinguish. Current is current and it doesn’t matter if it’s running a light, charging a battery or doing a little of both. The converter changes output voltage based on the current being drawn. No current being drawn and it sets at float voltage around 13.4V. A little current being drawn and it kicks the voltage up around 13.8V. More current being drawn and it kicks the output up around 14.5V. There are time limits applied to some of these settings to avoid overcharging the battery and to avoid constant switching.

Don’t try to make sense of what a WFCO manual says. It’s a step below gibberish when it comes to how they work. It actually says the converter output is 14.4V, but if you measure it you won’t measure 14.4V.

Now on to the converter/charger/battery issue. But first, a little bit of background...

I was expecting to do more dry camping so I put in a Battleborn lithium battery. Turns out I'm always plugged in now, so that was a waste but here we are. My thinking at the time was that the 9855 would not fully charge the lithium battery, but even at absorption voltage it wouldn't hurt the battery.

So now, moving forward with replacement, I still don't know what to do. It seems the ideal thing would be to keep the converter voltage at 14.6 and let the internal Battleborn charge controller manage the battery? Or just get another lithium compatible converter (even though none of them are more than semi smart)?

[jkwilson]

Thanks for confirming my thought process. This comes up again for me because I think my wf9855 might be failing so it's time to pick a better replacement.

First the failing 9855... I was watching my PD EMS display and saw a line current that was too high for what was running at the time. I cycled a few breakers until I found that the converter was drawing 8 amps (AC). The battery was disconnected at the time and when I power cycled the converter it was only drawing 3 amps (AC) with the same dc house loads. That looked more reasonable to me for refrigerator control, antenna amplifier, a few lights, etc. That tells me the converter is beginning to fail. It also explains my electricity bills being higher than I would expect. Does that diagnosis make sense?

It’s not too surprising to see the charging load change when you power cycle. Like I said above, there are timing components in the process as well as hysteresis to keep the output from cycling up and down when near a threshold. That can mean the charger is in one mode based on what it’s doing and how long ago it was told to do it, but resetting the power can give it a different goal. And WFCO’s implementation doesn’t seem to be great in that it doesn’t seem to respond fast enough at times.

[Jomani]

First the failing 9855... I was watching my PD EMS display and saw a line current that was too high for what was running at the time. I cycled a few breakers until I found that the converter was drawing 8 amps (AC). The battery was disconnected at the time and when I power cycled the converter it was only drawing 3 amps (AC) with the same dc house loads. That looked more reasonable to me for refrigerator control, antenna amplifier, a few lights, etc. That tells me the converter is beginning to fail. It also explains my electricity bills being higher than I would expect. Does that diagnosis make sense?

Your converter may indeed be failing, but I believe your diagnosis may be off a little. Electricity behaves much like water in a hose. Most of the time is just sitting there at a designated pressure (voltage) waiting for a place to go. When a load is applied (valve opened) current (water) flows at a rate determined by the amount of resistance (how far the valve is open).

If your theory were correct, your converter would have to be somehow absorbing all of the additional power internally. Since it’s primary function is to “convert” 120v AC to 12v DC (which does require a small amount of power) you haven’t yet discovered where that extra power is going. If you indicated that the converter was getting very hot or you smelled burning, then I would agree with you.

I would turn off all of the breakers and turn off all of the DC loads (that would require disconnecting the refrigerator and anything that does not go through the main DC panel). Then turn on only the converter breaker with no DC loads. Give that a few minutes to stabilize, then turn on the overhead lights and monitor the AC output. Next connect the refrigerator and again monitor. Keep adding loads and monitoring.

Your 55 amp converter should theoretically never exceed 660 watts output or the equivalent of 5.5 amps AC. In reality, it will exceed that if a high enough load exists. You just need to figure out what that load is.

As far as damaging your batteries, I wouldn’t be too concerned. Battle Born batteries have a superior BMS that will take care of the batteries. Lead acid and AGM batteries do not have this built-in safeguard and can easily be destroyed if a converter fails to switch charging modes when the battery reaches full charge.

[Fivecodys]

You can also reach out to WFCO technical support (574)294-8997.
I just got off the phone with them a few minutes ago. My Auto Detect for Lithium was not working and they had me send it back for a firmware upgrade under warranty. Very friendly people and they might be able to answer your questions.

[Roll With The Changes]

Your converter may indeed be failing, but I believe your diagnosis may be off a little. Electricity behaves much like water in a hose. Most of the time is just sitting there at a designated pressure (voltage) waiting for a place to go. When a load is applied (valve opened) current (water) flows at a rate determined by the amount of resistance (how far the valve is open).

If your theory were correct, your converter would have to be somehow absorbing all of the additional power internally. Since it’s primary function is to “convert” 120v AC to 12v DC (which does require a small amount of power) you haven’t yet discovered where that extra power is going. If you indicated that the converter was getting very hot or you smelled burning, then I would agree with you.

I would turn off all of the breakers and turn off all of the DC loads (that would require disconnecting the refrigerator and anything that does not go through the main DC panel). Then turn on only the converter breaker with no DC loads. Give that a few minutes to stabilize, then turn on the overhead lights and monitor the AC output. Next connect the refrigerator and again monitor. Keep adding loads and monitoring.

Your 55 amp converter should theoretically never exceed 660 watts output or the equivalent of 5.5 amps AC. In reality, it will exceed that if a high enough load exists. You just need to figure out what that load is.

As far as damaging your batteries, I wouldn’t be too concerned. Battle Born batteries have a superior BMS that will take care of the batteries. Lead acid and AGM batteries do not have this built-in safeguard and can easily be destroyed if a converter fails to switch charging modes when the battery reaches full charge.

Thanks for the input. Then AC current associated with the converter that I saw the other day was just a quick observation. I'm not getting obsessed with every load, but it did just occur to me that the refrigerator may have been running when I turned off the converter. Hence when I turned it back on and checked the AC current, the refrigerator had not had time to cycle back on. That explains the huge difference after power cycling the converter. I spoke prematurely before I fully understood what was happening. However...

I'm still frustrated by how these systems are set up. I'll expand in the next post.

[jkwilson]

Your converter may indeed be failing, but I believe your diagnosis may be off a little. Electricity behaves much like water in a hose. Most of the time is just sitting there at a designated pressure (voltage) waiting for a place to go. When a load is applied (valve opened) current (water) flows at a rate determined by the amount of resistance (how far the valve is open).

If your theory were correct, your converter would have to be somehow absorbing all of the additional power internally. Since it’s primary function is to “convert” 120v AC to 12v DC (which does require a small amount of power) you haven’t yet discovered where that extra power is going. If you indicated that the converter was getting very hot or you smelled burning, then I would agree with you.

I would turn off all of the breakers and turn off all of the DC loads (that would require disconnecting the refrigerator and anything that does not go through the main DC panel). Then turn on only the converter breaker with no DC loads. Give that a few minutes to stabilize, then turn on the overhead lights and monitor the AC output. Next connect the refrigerator and again monitor. Keep adding loads and monitoring.

Your 55 amp converter should theoretically never exceed 660 watts output or the equivalent of 5.5 amps AC. In reality, it will exceed that if a high enough load exists. You just need to figure out what that load is.

As far as damaging your batteries, I wouldn’t be too concerned. Battle Born batteries have a superior BMS that will take care of the batteries. Lead acid and AGM batteries do not have this built-in safeguard and can easily be destroyed if a converter fails to switch charging modes when the battery reaches full charge.

Don’t forget efficiency loss. Probably only an 85% conversion efficiency.

For the converter to supply 55A in charging mode, that’s 55A * 14.4V or 792W. If the converter is 85% efficient, which isn’t a stretch, you’d need to supply it with about 932W from shore power. That’s around 7.75A, so the 8A reading is not much of a stretch. It’s possible the converter is only around 80% efficient.