I am looking to buy a travel trailer this month (hopefully) and am planning on replacing the lead-acid battery with LiON (I have ordered a SOK 206AH battery based on Will Prowse's breakdown of that battery - of course, it hasn't been shipped yet). While I understand the basic issues that need to be addressed, I am finding it incredibly difficult to get accurate information about all the pieces and some of what I am finding is either conflicting or does not make sense to me given basic electronics. What I am looking for here is any information to fill in the blanks in what I am finding (or, more precisely, not finding) as well as confirmation of the assumptions I am making.
What is known:
My TV is a 2019 V6 Toyota Highlander to which I have added a 7-way RV plug (it came factory-wired with a 4-way plug). This provides an un-switched 12V circuit running from the TV battery to the 7-way plug. This wiring is 10 gauge copper from end-to-end with a 40A auto-reset circuit breaker near the TV battery on the positive wire.
What is maybe known:
I have had difficulty finding a definitive statement as to what sort of alternator is in the Highlander, but I have found some material that suggests it is a 150A alternator (unclear whether this is a "smart" alternator or not).
General claims about LiON batteries I've found in various places:
I have found several places that claim that LiON batteries do not require a "float" stage and that if one's charge controller has a "float" setting that it is pretty much irrelevant, but that setting it to 13.6V is acceptable.
I have also found conflicting claims about the "bulk" stage. Some places indicate that in this stage, the charger will deliver as much current as it can (which means that the output voltage will adjust to whatever level is necessary, given the battery's internal resistance, to reach the charger's maximal output current. But I've seen other places that specify a voltage for the "bulk" stage, which contradicts the notion that the charger will source as much current as it can during the "bulk" stage.
What I have found relating to charging a LiON battery from a TV's alternator:
There are multiple references that I've found that tying a TV's alternator directly to a LiON battery is a bad, bad idea for at least two reasons. First, the standard alternator does not generate the voltages required to properly charge a LiON. Second, the current draw of a LiON battery can burn out one's alternator.
The solution is to use a isolated DC/DC converter, which will both boost the voltage to the levels required to charge a LiON battery as well as regulate the current draw on the TV's alternator. After doing some research I'm looking at Victron Energy's Orion-Tr Smart DC-DC Isolated Charger primarily because it uses the voltage seen from the TV to decide whether the TV's engine is running or not (so no need to find a way to run a wire from the TV's ignition switch back to the trailer to control the DC/DC converter). There are two models of interest - the 12/12-18 and 12/12-30. Since the 10 gauge wire that runs from the TV through the 7-way plug is rated to carry 30A, the 12-12/30 is tempting, but it would seem to be right at the limit of what a 10-guage wire could safely carry, so I am opting for the Orion-Tr 12/12-18 model.
What I have found in downloaded manuals:
The trailer is solar-equipped with a 100W solar panel. The solar charge converter would appear to be a Jaboni 30A MPPT controller that apparently can charge multiple types of batteries, including lead-acid and LiON. The manual claims it supports a bulk/absorption/float cycle for LiON of 14.4V/14.4V/13.6V, but the "bulk" rating is highlighted in a different color than the rest of the chart, which makes me wonder if there really is a "bulk" mode that is distinct from the "absorption".
The AC/DC panel is a WFCO 8900-series unit. The WFCO AC/DC converter only supports lead-acid batteries. However there is a Progressive Dynamics PD4635 AC/DC converter that apparently can be swapped into the WFCO panel to replace the WFCO converter. The PD4635 is supposed to support both lead-acid and LiON batteries. However, the manual was a bit vague regarding what the stages are with LiON. So I wrote to the company and the email I received back indicated that there is a switch to toggle between lead-acid mode and LiON mode. In lead-acid mode there are 3 stages with varying output voltages. In LiON mode it outputs a steady 14.6V at all times - i.e. it is a single-stage charger.
The few pieces of information I can find on the SOK 206AH battery are a bit confusing. I was able to find a document on SOK's Facebook page that claims that the recommended amperage to charge the battery is 40A (yikes) a "recommended" charge voltage of 14.6V and a "balancing voltage" of <14.4V.
What I cannot find:
I cannot tell if there is any sort of isolator in the trailer between the 12V wire coming from the TV and the trailer's battery to prevent depleting the TV's battery. There is certainly no isolator in the TV.
.
What I am guessing at:
I am assuming that the output of the AC/DC converter, the Jaboni MPPT charge controller and the 12V un-switched circuit from the 7-way plug are all wired in parallel to the trailer's lead-acid battery and the internal 12V circuits. This means that any or all of the 3 possible charging sources (the AC/DC converter, the MPPT controller and the 12V wire from the TV) are driving the battery and internal 12V circuits in parallel.
I am assuming that when the BMS in the LiON battery cuts off the charger to avoid over-charging, that this is done using a diode, so that the battery can still source electricity to the trailer to operate the internal 12V circuits rather than leaving that entirely to the chargers (in general, having a charger directly drive a load instead of charging a battery seems to be a bad idea). I guess the AC/DC converter could drive the 12V loads directly since it is a simple, steady-state converter, but it seems like trying to directly drive a load from an MPPT controller or a DC/DC charger is a bad idea as they are trying to alter voltage levels based on the perceived charge of a battery.
Since the 12V circuit from the TV is incompatible with a LiON battery, I would have to interpose the DC/DC isolated charger between the 12V wire from the TV and the inputs to the LiON battery. So irrespective of whether there is an isolator already installed in the trailer, I will have to add my own to support the LiON battery.
I am assuming that the Orion-Tr 12/12-18 would not draw more than about 23A from the 12V wire from the TV (max continuous output is 18A at 15V with an 87% efficiency and an input activation voltage of no less than 13.3V -> (18A * 15V / 87%) / 13.3V = 23.3A). This value seems to be well within the range that a 10 gauge wire should be able to safely carry. The specs in the manuals do not actually indicate this parameter, so I am inferring it from the other parameters that are stated in the docs.
My questions:
1) The SOK battery docs that I can find talk about "recommended" and "balancing" voltages. It is not clear to me how this relates to the concepts of bulk/absorption/float found in the settings/specs of most chargers. I think I would set the "absorption" voltage to the "recommended" voltage value and the "float" voltage to the "balancing" voltage, but I'm not certain about this.
2) The Orion-Tr DC/DC charger seems to have bona fide bulk/absorption/float stages. It is not clear that the Jaboni has a bona fide "bulk" stage (meaning, variable voltage in order to achieve maximal current). The AC/DC converter in the PD4635 seems to be a simple, constant voltage output. Given that the charging profile of these three units are all slightly different form each other, is there a problem with having them wired in parallel to the trailer's LiON battery? I don't think that the minor differences between the Jaboni and Victron units would matter. The piece that I'm uncertain about is whether the constant voltage output of the PD4635 would cause a problem for the LiON battery.
3) The 100W solar panel would generate no more than 6.8A at 14.6 volts, and the Orion-Tr would cap out at 18A. This means that at best, while towing the vehicle, I would get 24.8A to charge the LiON battery, when the recommended amperage is 40A. When only on solar, I am limited to about 6.8A. I assume this simply means that my battery would charge slowly but would not otherwise reduce the battery's lifespan or otherwise damage the battery.
4) Regarding the single-stage output of the Progressive Dynamics PD4635 modules, one option I've considered is to wire the output of the AC/DC converter into a second DC/DC converter (specifically, a Renogy DCC50S) and then wire the output of the DC/DC converter to the LiON battery et al. This would provide for a bona fide 3-stage charger when power is coming from the shore line. Question is, does this make sense or is it over-engineering?
What is known:
My TV is a 2019 V6 Toyota Highlander to which I have added a 7-way RV plug (it came factory-wired with a 4-way plug). This provides an un-switched 12V circuit running from the TV battery to the 7-way plug. This wiring is 10 gauge copper from end-to-end with a 40A auto-reset circuit breaker near the TV battery on the positive wire.
What is maybe known:
I have had difficulty finding a definitive statement as to what sort of alternator is in the Highlander, but I have found some material that suggests it is a 150A alternator (unclear whether this is a "smart" alternator or not).
General claims about LiON batteries I've found in various places:
I have found several places that claim that LiON batteries do not require a "float" stage and that if one's charge controller has a "float" setting that it is pretty much irrelevant, but that setting it to 13.6V is acceptable.
I have also found conflicting claims about the "bulk" stage. Some places indicate that in this stage, the charger will deliver as much current as it can (which means that the output voltage will adjust to whatever level is necessary, given the battery's internal resistance, to reach the charger's maximal output current. But I've seen other places that specify a voltage for the "bulk" stage, which contradicts the notion that the charger will source as much current as it can during the "bulk" stage.
What I have found relating to charging a LiON battery from a TV's alternator:
There are multiple references that I've found that tying a TV's alternator directly to a LiON battery is a bad, bad idea for at least two reasons. First, the standard alternator does not generate the voltages required to properly charge a LiON. Second, the current draw of a LiON battery can burn out one's alternator.
The solution is to use a isolated DC/DC converter, which will both boost the voltage to the levels required to charge a LiON battery as well as regulate the current draw on the TV's alternator. After doing some research I'm looking at Victron Energy's Orion-Tr Smart DC-DC Isolated Charger primarily because it uses the voltage seen from the TV to decide whether the TV's engine is running or not (so no need to find a way to run a wire from the TV's ignition switch back to the trailer to control the DC/DC converter). There are two models of interest - the 12/12-18 and 12/12-30. Since the 10 gauge wire that runs from the TV through the 7-way plug is rated to carry 30A, the 12-12/30 is tempting, but it would seem to be right at the limit of what a 10-guage wire could safely carry, so I am opting for the Orion-Tr 12/12-18 model.
What I have found in downloaded manuals:
The trailer is solar-equipped with a 100W solar panel. The solar charge converter would appear to be a Jaboni 30A MPPT controller that apparently can charge multiple types of batteries, including lead-acid and LiON. The manual claims it supports a bulk/absorption/float cycle for LiON of 14.4V/14.4V/13.6V, but the "bulk" rating is highlighted in a different color than the rest of the chart, which makes me wonder if there really is a "bulk" mode that is distinct from the "absorption".
The AC/DC panel is a WFCO 8900-series unit. The WFCO AC/DC converter only supports lead-acid batteries. However there is a Progressive Dynamics PD4635 AC/DC converter that apparently can be swapped into the WFCO panel to replace the WFCO converter. The PD4635 is supposed to support both lead-acid and LiON batteries. However, the manual was a bit vague regarding what the stages are with LiON. So I wrote to the company and the email I received back indicated that there is a switch to toggle between lead-acid mode and LiON mode. In lead-acid mode there are 3 stages with varying output voltages. In LiON mode it outputs a steady 14.6V at all times - i.e. it is a single-stage charger.
The few pieces of information I can find on the SOK 206AH battery are a bit confusing. I was able to find a document on SOK's Facebook page that claims that the recommended amperage to charge the battery is 40A (yikes) a "recommended" charge voltage of 14.6V and a "balancing voltage" of <14.4V.
What I cannot find:
I cannot tell if there is any sort of isolator in the trailer between the 12V wire coming from the TV and the trailer's battery to prevent depleting the TV's battery. There is certainly no isolator in the TV.
.
What I am guessing at:
I am assuming that the output of the AC/DC converter, the Jaboni MPPT charge controller and the 12V un-switched circuit from the 7-way plug are all wired in parallel to the trailer's lead-acid battery and the internal 12V circuits. This means that any or all of the 3 possible charging sources (the AC/DC converter, the MPPT controller and the 12V wire from the TV) are driving the battery and internal 12V circuits in parallel.
I am assuming that when the BMS in the LiON battery cuts off the charger to avoid over-charging, that this is done using a diode, so that the battery can still source electricity to the trailer to operate the internal 12V circuits rather than leaving that entirely to the chargers (in general, having a charger directly drive a load instead of charging a battery seems to be a bad idea). I guess the AC/DC converter could drive the 12V loads directly since it is a simple, steady-state converter, but it seems like trying to directly drive a load from an MPPT controller or a DC/DC charger is a bad idea as they are trying to alter voltage levels based on the perceived charge of a battery.
Since the 12V circuit from the TV is incompatible with a LiON battery, I would have to interpose the DC/DC isolated charger between the 12V wire from the TV and the inputs to the LiON battery. So irrespective of whether there is an isolator already installed in the trailer, I will have to add my own to support the LiON battery.
I am assuming that the Orion-Tr 12/12-18 would not draw more than about 23A from the 12V wire from the TV (max continuous output is 18A at 15V with an 87% efficiency and an input activation voltage of no less than 13.3V -> (18A * 15V / 87%) / 13.3V = 23.3A). This value seems to be well within the range that a 10 gauge wire should be able to safely carry. The specs in the manuals do not actually indicate this parameter, so I am inferring it from the other parameters that are stated in the docs.
My questions:
1) The SOK battery docs that I can find talk about "recommended" and "balancing" voltages. It is not clear to me how this relates to the concepts of bulk/absorption/float found in the settings/specs of most chargers. I think I would set the "absorption" voltage to the "recommended" voltage value and the "float" voltage to the "balancing" voltage, but I'm not certain about this.
2) The Orion-Tr DC/DC charger seems to have bona fide bulk/absorption/float stages. It is not clear that the Jaboni has a bona fide "bulk" stage (meaning, variable voltage in order to achieve maximal current). The AC/DC converter in the PD4635 seems to be a simple, constant voltage output. Given that the charging profile of these three units are all slightly different form each other, is there a problem with having them wired in parallel to the trailer's LiON battery? I don't think that the minor differences between the Jaboni and Victron units would matter. The piece that I'm uncertain about is whether the constant voltage output of the PD4635 would cause a problem for the LiON battery.
3) The 100W solar panel would generate no more than 6.8A at 14.6 volts, and the Orion-Tr would cap out at 18A. This means that at best, while towing the vehicle, I would get 24.8A to charge the LiON battery, when the recommended amperage is 40A. When only on solar, I am limited to about 6.8A. I assume this simply means that my battery would charge slowly but would not otherwise reduce the battery's lifespan or otherwise damage the battery.
4) Regarding the single-stage output of the Progressive Dynamics PD4635 modules, one option I've considered is to wire the output of the AC/DC converter into a second DC/DC converter (specifically, a Renogy DCC50S) and then wire the output of the DC/DC converter to the LiON battery et al. This would provide for a bona fide 3-stage charger when power is coming from the shore line. Question is, does this make sense or is it over-engineering?
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