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#21 eyemgh

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Posted 12 August 2021 - 02:55 PM

Following. 


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#22 Jon R

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Posted 12 August 2021 - 05:29 PM

Hi Bryan,

This is not rocket science, but it does require a basic understanding of DC circuits and battery behavior. If you are not confident about tackling those areas, I would suggest getting some help beyond internet forum discussions. You should be confident you know what you are doing - not just following advice from strangers.

That said, the reason a DC to DC converter is typically needed to effectively charge a LiFePO battery from a typical modern truck electrical system is the DC voltage that can be supplied by the truck alternator at the end of the long wire run to a camper or trailer battery is that the voltage at the end of the wire run is not sufficient to quickly or fully charge the LiFePO battery.

LiFePO batteries typically need the charging source to be able to deliver 14.2 to 14.6 volts at the battery. A modern smart alternator may supply 14.5 to 15 volts at the truck battery, but when you add the resistive loss of the 40 to 50 feet of wire to and from the camper battery, depending on wire gage, 13.5 volts or lower is supplied at the camper battery if, say, 30 amps are being drawn. This loss will limit the charging current supplied to the camper battery, resulting in a much slower charging process and potentially never fully charging the camper battery.

A DC to DC converter is typically installed to address this issue. Its function is to step up the DC voltage supplied to the camper battery to the desired level, and to control battery charging voltlage and current. To do this effectively it needs to be installed near the camper battery so the wire losses between the charger and charging battery are minimized.

A second important function that the DC to DC converter performs is to limit the charging current supplied to the LiFePO battery when it is significantly discharged. The “internal resistance” of these batteries is low, so they can pull very high charging current when discharged to a low level. A typical camper installation is likely protected for this by the resistance if the wiring from the truck to the camper, but it can be an issue for short wire runs. Regularly pulling the max current your alternator can deliver can prematurely wear out the alternator or overheat inadequately fused wires.
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#23 BryanToyFWC

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Posted 12 August 2021 - 07:30 PM

Hi Bryan,

This is not rocket science, but it does require a basic understanding of DC circuits and battery behavior. If you are not confident about tackling those areas, I would suggest getting some help beyond internet forum discussions. You should be confident you know what you are doing - not just following advice from strangers.

That said, the reason a DC to DC converter is typically needed to effectively charge a LiFePO battery from a typical modern truck electrical system is the DC voltage that can be supplied by the truck alternator at the end of the long wire run to a camper or trailer battery is that the voltage at the end of the wire run is not sufficient to quickly or fully charge the LiFePO battery.

LiFePO batteries typically need the charging source to be able to deliver 14.2 to 14.6 volts at the battery. A modern smart alternator may supply 14.5 to 15 volts at the truck battery, but when you add the resistive loss of the 40 to 50 feet of wire to and from the camper battery, depending on wire gage, 13.5 volts or lower is supplied at the camper battery if, say, 30 amps are being drawn. This loss will limit the charging current supplied to the camper battery, resulting in a much slower charging process and potentially never fully charging the camper battery.

A DC to DC converter is typically installed to address this issue. Its function is to step up the DC voltage supplied to the camper battery to the desired level, and to control battery charging voltlage and current. To do this effectively it needs to be installed near the camper battery so the wire losses between the charger and charging battery are minimized.

A second important function that the DC to DC converter performs is to limit the charging current supplied to the LiFePO battery when it is significantly discharged. The “internal resistance” of these batteries is low, so they can pull very high charging current when discharged to a low level. A typical camper installation is likely protected for this by the resistance if the wiring from the truck to the camper, but it can be an issue for short wire runs. Regularly pulling the max current your alternator can deliver can prematurely wear out the alternator or overheat inadequately fused wires.

 

Thanks for kindly pointing out that I have no idea what I'm doing, because it's true!  Also thank you for the summary on DC-DC, makes sense.

 

I'd love to pay a nice person to help with this part, but our local FWC people have been a little unresponsive lately.  Seems like everyone else in this space is very busy as well.  So unfortunately I'm left to figure it out and ask strangers on the internet.  

 

Like I said, I'm handy, but not savvy with electricity (finance is my gig....).  I can connect the right wires to the right stuff with the right map.  All I really know is my fully charged batteries, straight from shore power, are dead by morning with nothing else running but the fridge.  They are 5 years old, right about time to die.  So, want to upgrade and the more I think about it, Li is starting to sound like the plan, just need to figure it out. 

 

Thanks!!


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#24 Jon R

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Posted 12 August 2021 - 08:52 PM

Sorry Bryan if my first paragraph came across as insulting.  I didn't mean it that way.  I also didn't mean to imply that you should have a dealer do this rather than attempting a DIY project.  I just think that having a person you can go to for guidance and sanity checks is going to be a big help over trying to teach yourself by research and forum discussions alone.  You can save a lot of money doing this project yourself, but as you are acknowledging, it needs to be done properly to be safe. 


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#25 rando

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Posted 13 August 2021 - 12:18 AM

For now, you can just buy a 100Ah LiFePO4 battery and drop it into the camper as a straight replacement for the lead acid battery.    While this won't be 100% optimal, it won't hurt anything and it will work better than your failing lead acid batteries.  If you buy a battery with built in bluetooth, you will also get monitoring of your battery, so you can see how it is doing and assess if you need to change anything else. 

 

As you figure things out and learn you can decide if you need a DC-DC charger, or it you need to change/upgrade your solar controller.  There is no real need to do everything at once. 


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#26 BryanToyFWC

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Posted 13 August 2021 - 03:38 PM

Sorry Bryan if my first paragraph came across as insulting.  I didn't mean it that way.  I also didn't mean to imply that you should have a dealer do this rather than attempting a DIY project.  I just think that having a person you can go to for guidance and sanity checks is going to be a big help over trying to teach yourself by research and forum discussions alone.  You can save a lot of money doing this project yourself, but as you are acknowledging, it needs to be done properly to be safe. 

Jon, no need to be sorry!  Not insulted at all. I’m new to this stuff and I know it!  
 

Would love to find someone to help me think through. Anyone live in Denver?


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#27 NRVhawk

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Posted 13 August 2021 - 09:23 PM

Hey Bryan, it looks like you've gotten a lot of good advice here.  One thing that I noticed is that you mentioned using the LIFEPO IQ4 module with your Iota charger.  Since you've got a 2017 FWC, I suspect that your charger is a DLS-30/IQ4 charger that FWC installs in later models (my 2016 Hawk has one).   That charger has the IQ4 circuit built into the charger, and the LIFEPO module won't work with it.  To use the LIFEPO module, you need a DLS-30 charger.  You can tell what you have by looking at the label on the top of the unit, which identifies the model.  Also, there's a label next to the RJ-11 telephone-style jack that says "Dual voltage jack disabled" if it's incompatible with the LIFEPO module.

 

Wish I lived near Denver to lend you a hand.  I'm in the middle of switching my camper over to LIFePO4 now, and hope to finish up this weekend.   As Jon said, it would be helpful (and safer) to have someone who is familiar with working with DC circuits to help.  There are some tools, like strippers, crimpers, torque wrench/screwdriver, wire labels, and multimeter that would help.

 

- Rusty


Edited by NRVhawk, 13 August 2021 - 09:24 PM.

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#28 goinoregon

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Posted 14 August 2021 - 01:00 AM

bryan. i find it hard to believe that local fwc wont communicate about a battery and controller, etc. upgrade. they sell things, that is their business. maybe u need to just walk in the door, and talk ?.  here in pdx, i bought a lifpo battery, alucab awning, and a few other things from local fwc dealer. all went well. then had them install alucab awning. no problems.

i have an atc shell.  while i was waiting for it, i watched for local wtw posts for local folks. hit em up, and asked to visit and see their layouts. learned a lot, met some great folks. picked their brains, etc. 

one of the fellows i met, is an retired electrical engineer  :) .  he is a wtw member. he lives within a mile of me here in pdx. he made an electrical pick list in 3 emails, with amazon links for products.  i bought all the stuff. my new friend came over 3 times, and we put it all together, to power the battery from solar panels.

i got lucky.

but i would recommend actively finding wtw folks in denver area. there are probably way more than here in pdx.  and, physically walking into fwc dealer.   and i dont know why a local rv dealership would not be a resource


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#29 Outnabout

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Posted 14 August 2021 - 03:59 AM

For now, you can just buy a 100Ah LiFePO4 battery and drop it into the camper as a straight replacement for the lead acid battery. While this won't be 100% optimal, it won't hurt anything and it will work better than your failing lead acid batteries. If you buy a battery with built in bluetooth, you will also get monitoring of your battery, so you can see how it is doing and assess if you need to change anything else.

As you figure things out and learn you can decide if you need a DC-DC charger, or it you need to change/upgrade your solar controller. There is no real need to do everything at once.


Does the Bluetooth in the battery give the same information as a shunt? What is the difference between the two?
Thanks
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#30 rando

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Posted 14 August 2021 - 01:54 PM

Does the Bluetooth in the battery give the same information as a shunt? What is the difference between the two?
Thanks

 

Yes it does - most provide state of charge, voltage, current in/out of the battery, internal temperature etc.     Additionally, they typically provide the individual cell level voltages so you know everything is OK within the battery.  The exact details of what is reported depend on the particular battery, but most seem to be using a similar internal BMS.   The SOC is calculated using coulomb counting (Ah in minus Ah out) just like a Victron BMV.

 

I have both a bluethooth enabled BMS and a Victron BMV - the SOC is typically within a few % of each other.  I typically look at the data from the BMS because it gives me more detail.  If I were starting again, I would skip the Victron BMV.  While the BMV is a great piece of equipment, the battery directly provides what I need to know. 


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