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Old 11-27-2021, 09:00 PM   #1
ACJ
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Lithium Batteries

I am considering lithium batteries and have done some searching on the forum but have a few questions.

Converter is WFCO WF-8735P (https://wfcoelectronics.com/product/wf-8735-35-amp/) Nominal voltage output modes are a 13.2 VDC range “float” mode, 13.6 VDC range “absorption” charge mode, and a 14.4 VDC range “bulk” charge mode.

- From what I've read it appears that without replacing the converter I will only get a charge up to 90%?

- Concern about the TV battery pulling from the Lithium. If I understand correctly this is really only an issue when the TV is not running, is that correct?

I will be installing a battery disconnect switch right off the battery so my thought was that if stopped or parked (staying at a hotel for a night on a long trip) I would simply be able to disconnect the battery so there is no draw from the TV battery. Would that work?

- I'd like to keep the batteries on the tounge in the factory box. Is there any concern about this other then temperature?

I do camp in the spring and fall where temperatures can be lower overnight but usually warm up during the day. I would not be charging then only drawing from the battery with lithium temp when drawing doesn't matter. Also I would get a battery with BMS with cold shut off so in the event something would try to charge (potential solar setup or TV) the battery would not accept it. Is there any concern relying on the battery BMS to not let the battery charge?

I know some have moved them inside the trailer but with an aframe space is limited so I'd prefer not to move them inside.
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Old 11-27-2021, 10:09 PM   #2
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Originally Posted by ACJ View Post
I am considering lithium batteries and have done some searching on the forum but have a few questions.

Converter is WFCO WF-8735P (https://wfcoelectronics.com/product/wf-8735-35-amp/) Nominal voltage output modes are a 13.2 VDC range “float” mode, 13.6 VDC range “absorption” charge mode, and a 14.4 VDC range “bulk” charge mode.

- From what I've read it appears that without replacing the converter I will only get a charge up to 90%?

- Concern about the TV battery pulling from the Lithium. If I understand correctly this is really only an issue when the TV is not running, is that correct?

I will be installing a battery disconnect switch right off the battery so my thought was that if stopped or parked (staying at a hotel for a night on a long trip) I would simply be able to disconnect the battery so there is no draw from the TV battery. Would that work?

- I'd like to keep the batteries on the tounge in the factory box. Is there any concern about this other then temperature?

I do camp in the spring and fall where temperatures can be lower overnight but usually warm up during the day. I would not be charging then only drawing from the battery with lithium temp when drawing doesn't matter. Also I would get a battery with BMS with cold shut off so in the event something would try to charge (potential solar setup or TV) the battery would not accept it. Is there any concern relying on the battery BMS to not let the battery charge?

I know some have moved them inside the trailer but with an aframe space is limited so I'd prefer not to move them inside.
You'll want to replace the power center. The Lithium power center replacement is the WF-8735LiS. https://wfcoelectronics.com/product/wf-8735lis/ Not a difficult change out.

Unplug from the TV, no switch needed.

You'll have to hunt for a lithium battery that will fit the factory box. I found this vendor https://lithiummarinebattery.com/shop has batteries that will fit and have a BMS with low temperature shut-off. The only concern is battery theft.
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Old 11-28-2021, 12:57 AM   #3
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You don't need the entire power center to switch to lithium, just changing out the converter is fine. Much easier, the wires in, 2 wires out.

As for drawing from your TV, it depends on your TV. Many vehicles disconnect the trailer circuit when the vehicle is off. You can test your plug with a voltmeter. The other option is to simply disconnect the plug as noted above
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Old 11-28-2021, 11:37 AM   #4
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You don't need the entire power center to switch to lithium, just changing out the converter is fine. Much easier, the wires in, 2 wires out.

As for drawing from your TV, it depends on your TV. Many vehicles disconnect the trailer circuit when the vehicle is off. You can test your plug with a voltmeter. The other option is to simply disconnect the plug as noted above
The WFCO 30 amp system, WF-8735P must be completely replaced. The converter cannot be replaced as a separate unit. On the larger power centers the converter can be replaced separately.
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Old 11-28-2021, 12:35 PM   #5
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The WFCO 30 amp system, WF-8735P must be completely replaced. The converter cannot be replaced as a separate unit. On the larger power centers the converter can be replaced separately.
That sucks
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Old 11-28-2021, 12:55 PM   #6
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You could also install the Progressive Dynamics model PD4135K. It is a replacement for the WF-8735lis
https://www.etrailer.com/p-PD4135K.html
or upgrade to the WF-8735LiS if you can find one.
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Old 11-28-2021, 02:10 PM   #7
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You should read this post I did on that converter with lithium batteries

https://www.forestriverforums.com/fo...es-240825.html
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Old 11-28-2021, 06:29 PM   #8
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Originally Posted by ACJ View Post
I am considering lithium batteries and have done some searching on the forum but have a few questions.

Converter is WFCO WF-8735P (https://wfcoelectronics.com/product/wf-8735-35-amp/) Nominal voltage output modes are a 13.2 VDC range “float” mode, 13.6 VDC range “absorption” charge mode, and a 14.4 VDC range “bulk” charge mode.
As noted by others, and the link provided above, your converter is not ideal. Normally I would suggest giving it a try. But, in this case, that's probably a waste of time. Here are the issues:

To avoid going through bulk mode (up to 14.4V) needlessly, the converter waits for a low voltage that indicates at least some charging is necessary. This is usually around 12.6V for a lead-acid battery. Since the voltage from a lithium battery will rarely if ever get that low, the converter may never go into bulk mode. This was what I found with my WFCO 8955. I could only ever get float mode.

Your float mode at 13.2V will charge a LiFePO4 only up to about 75-80% and may take days to do so. So it's pretty useless.

The 13.6V absorb mode would charge a LiFePO4 to 100% if you could get the charger into that mode, but the only way to get there is to go through bulk mode which you likely will never see.

In conclusion, since 13.2 V charging is pretty useless, you are stuck with buying a lithium-specific converter.

If you want to try salvaging the converter you have, you could do some testing to see if you can get it into bulk and absorb modes maybe using the trick titanmike suggested.

While my WFCO 8955 would not go into bulk mode, I did fine a "pot" on the control board that adjusts float mode voltage. I can set it as high as 14.2V. Since this converter always goes into float mode, I have used it as a charger (set at 14.2V) and a float device (set at 13.5V). I don't think this is a solution for your charging needs, but if you replace the converter, you might find the old one useful in some way.
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Old 11-28-2021, 07:01 PM   #9
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The WFCO is capable of charging lithium batteries fully as per my post above, just with a few things to keep in mind
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Old 11-28-2021, 10:04 PM   #10
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The WFCO is capable of charging lithium batteries fully as per my post above, just with a few things to keep in mind
Sure, if you are okay with .......
"Before I get very long winded, the WFCO 8735 is completely capable of charging a lithium battery up to at least 90% and sometimes 100% but the key is that the battery has to be at an extremely low state of charge to do so."
This and the other caveats in that article are not what I would want to live with, or would suggest to anyone else, in a lithium charger.
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Old 11-28-2021, 11:14 PM   #11
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Thanks everyone for the good info.

When connected to shore power does the battery still provide a purpose or does the converter simply take the 120V and convert it into 12V and the battery is not used?
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Old 11-29-2021, 02:58 AM   #12
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Thanks everyone for the good info.

When connected to shore power does the battery still provide a purpose or does the converter simply take the 120V and convert it into 12V and the battery is not used?
Very astute question. It should come up more often than it does. The converter is typically a two or three stage charger that ends up in float mode. Float mode holds the battery at 100% SOC by holding voltage constant, usually around 13.5 or 13.6V. By holding the voltage constant, the battery current sits at zero and the converter picks up all 12V load that is placed on the system up to its current rating. Higher loads would take current from the converter and the battery. Of course, shore power normally covers the 120V loads thus leaving only the modest 12V loads (heater fan, water pump, etc.) on the converter.

So, generally the battery is not used when on shore power though it remains connected. Indeed, one could disconnect the battery and the converter would still hold that 13.5 or 13.6 volts and power the 12V loads.
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Old 11-29-2021, 09:32 AM   #13
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Very astute question. It should come up more often than it does. The converter is typically a two or three stage charger that ends up in float mode. Float mode holds the battery at 100% SOC by holding voltage constant, usually around 13.5 or 13.6V. By holding the voltage constant, the battery current sits at zero and the converter picks up all 12V load that is placed on the system up to its current rating. Higher loads would take current from the converter and the battery. Of course, shore power normally covers the 120V loads thus leaving only the modest 12V loads (heater fan, water pump, etc.) on the converter.

So, generally the battery is not used when on shore power though it remains connected. Indeed, one could disconnect the battery and the converter would still hold that 13.5 or 13.6 volts and power the 12V loads.
Thanks. So if camping with shore power and the battery is not really used and when boondocking the converter is not really used since you are using the battery why even worry about replacing the converter?

Our trips are usually 3-5 days or a week. So if there is no shore power I don't have the ability to plug in for the converter to charge the battery. I am charging the battery before we leave and then charging again when we get back home with a stand alone charger. My plan is also depending on need to look into a solar setup for charging when boondocking.

Am I missing something? When would I need to rely on the converter for charging the battery?
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Old 11-29-2021, 12:04 PM   #14
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Thanks. So if camping with shore power and the battery is not really used and when boondocking the converter is not really used since you are using the battery why even worry about replacing the converter?

Our trips are usually 3-5 days or a week. So if there is no shore power I don't have the ability to plug in for the converter to charge the battery. I am charging the battery before we leave and then charging again when we get back home with a stand alone charger. My plan is also depending on need to look into a solar setup for charging when boondocking.

Am I missing something? When would I need to rely on the converter for charging the battery?
If planning on installing Solar then replacing the Converter is TOTALLY an option. Solar will provide the necessary cell balancing if the solar controller is set for LiFePo4 battery charging. Solar will also work when in storage even with no shore power connection.

Sometining about LiFePo4 batteries that tend to favor using the old converter if you already have one.

LiFePo4 batteries really shouldn't be stored at 100% SOC for more than a few weeks. According to many mfr's they do quite well sitting around the same voltage as most conventional charger's float voltage.

Cell balancing is really only necessary when the LiFePo4 batteries have been deep cycled frequently. Cells don't discharge at exactly the same rate so after time they will become imbalanced. Unlike Lead/Acid batteries no damage is done and only capacity is diminished. Once voltage is raised above 14 volts the BMS rebalances the cells. If you install Solar that part is handled from solar output.

If one is boondocking regularly more likely than not the Solar is handling cell balancing and the converter is just there for powering the 12v system when hooked to shore power or running a generator.

In short, replacing the converter is not a general requirement.

Even if not installing solar, a simple and inexpensive "hack" is to purchase a LiFePo4 capable battery maintainer, hook it to batteries, plug it into an 120vac source in the RV, and whenever on shore power/generator the batteries will be topped off with cells balanced. Less than half the cost of a new converter.
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Old 11-29-2021, 12:37 PM   #15
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If planning on installing Solar then replacing the Converter is TOTALLY an option. Solar will provide the necessary cell balancing if the solar controller is set for LiFePo4 battery charging. Solar will also work when in storage even with no shore power connection.

Sometining about LiFePo4 batteries that tend to favor using the old converter if you already have one.

LiFePo4 batteries really shouldn't be stored at 100% SOC for more than a few weeks. According to many mfr's they do quite well sitting around the same voltage as most conventional charger's float voltage.

Cell balancing is really only necessary when the LiFePo4 batteries have been deep cycled frequently. Cells don't discharge at exactly the same rate so after time they will become imbalanced. Unlike Lead/Acid batteries no damage is done and only capacity is diminished. Once voltage is raised above 14 volts the BMS rebalances the cells. If you install Solar that part is handled from solar output.

If one is boondocking regularly more likely than not the Solar is handling cell balancing and the converter is just there for powering the 12v system when hooked to shore power or running a generator.

In short, replacing the converter is not a general requirement.

Even if not installing solar, a simple and inexpensive "hack" is to purchase a LiFePo4 capable battery maintainer, hook it to batteries, plug it into an 120vac source in the RV, and whenever on shore power/generator the batteries will be topped off with cells balanced. Less than half the cost of a new converter.
Thanks, Mike. I was holding off on mentioning the solar to try to understand the converter/lithium relationship first. I will likely need some type of solar though because the batteries are not going to last on the longer 4-5 day trips and especially the week long trips.

Assuming I wouldn't have solar I understand the "hack" but if the battery is not used when hooked up to shore power why would you ever have to do this? If you have shore power it seems you don't even need the battery.

The only time I can see needing to do this is if you are on a very long trip and switching back and fourth between shore power and boondocking. At some point you then need a way to charge the batteries. With my trips being shorter I either get a site with shore power or don't and then boondock relying on the battery.

If boondocking my thought was to just charge the batteries once back home.

For me the thought with Lithium is I can possibly get away with only 1 battery instead of 2 - 6v batteries. That is a significant weight difference plus all the other advantages of lithium.
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Old 11-29-2021, 01:37 PM   #16
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Thanks. So if camping with shore power and the battery is not really used and when boondocking the converter is not really used since you are using the battery why even worry about replacing the converter?

Our trips are usually 3-5 days or a week. So if there is no shore power I don't have the ability to plug in for the converter to charge the battery. I am charging the battery before we leave and then charging again when we get back home with a stand alone charger. My plan is also depending on need to look into a solar setup for charging when boondocking.

Am I missing something? When would I need to rely on the converter for charging the battery?
Another good one. I do not have a converter. I took it out several years ago when it was clear we would probably never be on shore power again. I converted it to a bench power supply for my Li battery building projects.

Some years ago we were in an RV park two nights out of necessity, but we did not use the shore power.
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Old 11-29-2021, 01:42 PM   #17
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For me the thought with Lithium is I can possibly get away with only 1 battery instead of 2 - 6v batteries. That is a significant weight difference plus all the other advantages of lithium.
I think you are a candidate for a "suitcase" solar system (ready made or home brew). One you only set out if the Li battery gets really low and you aren't ready to head home.
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Old 11-29-2021, 01:52 PM   #18
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Thanks, Mike. I was holding off on mentioning the solar to try to understand the converter/lithium relationship first. I will likely need some type of solar though because the batteries are not going to last on the longer 4-5 day trips and especially the week long trips.

Assuming I wouldn't have solar I understand the "hack" but if the battery is not used when hooked up to shore power why would you ever have to do this? If you have shore power it seems you don't even need the battery.

The only time I can see needing to do this is if you are on a very long trip and switching back and fourth between shore power and boondocking. At some point you then need a way to charge the batteries. With my trips being shorter I either get a site with shore power or don't and then boondock relying on the battery.

If boondocking my thought was to just charge the batteries once back home.

For me the thought with Lithium is I can possibly get away with only 1 battery instead of 2 - 6v batteries. That is a significant weight difference plus all the other advantages of lithium.
The "hack" is just an affordable way to charge the batteries on shore power without buying a new converter/charger.

I don't have a converter in my big, fancy system either. I had a stand alone converter/charger and installed an inverter/charger (Victron Multiplus II). The way the inverter/charger works is it always powers the DC loads with the batteries. When the batteries need charging and hooked to shore power, the Multiplus charges them from shore power. If no shore power, the batteries run everything and don't get charged unless I turn on the solar.

The "hack" would be the same thing. Buy this $65 Li charger and you will have the same thing that I have but at 1/20 the cost.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

This would give you the ability to extend your boondocking trips with a generator as well.
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Old 11-29-2021, 04:42 PM   #19
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One thing to note on LiFePo4 batteries is their different charging curve. As the SOC rises and cell voltages approach 3.5v per cell (14 v for a "12v" battery) very little energy is added to the battery on it's way to 14.6v (max of 3.65v per cell) just cell balancing.

Once charging ceases the battery voltage will slowly drop on it's own to ~13.85 v.

Other than for cell balancing one shouldn't be overly concerned with voltages and voltage/SOC charts for LiFePo4 batteries can cause more confusion than they help.

Monitoring with a coulomb counting monitor will relieve battery anxiety. Just periodically top off so both battery and monitor synchronize at 100%.
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