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Olddawgsrule 
Senior Member 
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
 Topic: Lithium Battery install ?Posted: 24 Oct 2019 at 9:18am |
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Done a bit of research on these B to B units. I have a decent grasp on how they work now. What I'm reading is how well they recharge depends heavily on the SOC at beginning and duration. Certainly not a lone source for recharge.. We travel for months. Typically only staying put a few days. Currently (with my PbA's) I can go 3 days of real tough solar gain and catch the batt's up while driving to our next destination. I really don't wish to lose this benefit of TV charging. |
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offgrid
Senior Member
Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 24 Oct 2019 at 9:39am |
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Sounds like you are mostly boon docking, like me. Then maybe skip the ac (WFCO replacement) charger and just use tow vehicle and solar charging? That's my plan when I convert to Li. One nice thing about Li batts is that it doesn't hurt to leave them at partial SOC for long periods, which can be devastating for PbA's.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Olddawgsrule
Senior Member
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
Posted: 24 Oct 2019 at 3:18pm |
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Okay.. Biggest part of research right now is: How will you stop the WFCO charger? Or will you? I've read good points on both sides of the fence on this one...
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Olddawgsrule
Senior Member
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
Posted: 24 Oct 2019 at 4:27pm |
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Okay, I wasn't going to, but I guess I will... jump in the deep end of the pool.. It seems to me that the only reason to swap out the converter/charger is so the LiPo could get to full charge. That is for those that use shore power regularly. Now, for $180, I can switch out and have that opportunity and the unit is adjustable in it's ranges. Meaning, I can use my portable for now and upgrade later. As far as the B to B goes, we're looking at a circuit built up from modules that are easily purchased. I'll stop there for now until more is learned and worked through. I am also chasing 2 batteries right now. Nov 11th is the sale day for anything purchased out of China. If you know what you want (which I hope I do at that point), watch for a deal! Actually watch that whole week.. splash deals come and go quickly. I'm researching the Companies now. |
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offgrid
Senior Member
Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 24 Oct 2019 at 8:10pm |
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I plan to just remove the wfco. It will not be needed. I want to go with a 24Vdc Li battery, a 24V MPPT solar charge controller, and a 12 to 24V dc/dc converter from the TV. I'll have a small 24 to 12 Vdc converter to run the existing 12Vdc loads in the trailer, and a 2 to 3 kw 24Vdc to 120Vac inverter to run the heavy a/c and microwave loads. Everything is more efficient and you need much less copper conductor at 24V, and there are great deals available on 24V battery packs from wrecked Teslas. If I have 120Vac grid power available I can run the heavy loads directly on that. The 12Vdc loads are so small compared to the system I want to install that I don't ever expect to need to charge from the grid for that anyway. The solar will take care of it.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Olddawgsrule
Senior Member
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
Posted: 25 Oct 2019 at 9:02am |
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Let's get into this B to B a little better please. I wish to see if I'm really understanding..
Seems I could run with a 12V 20a unit. If I place the efficiency at 80% (wiring, unit, etc..), I'm looking at 16amps now. Is that a good assumption? Then I'm curious if indeed I will get the 16amps continuously. What can you really expect over a 4 hour period? 64amps (using my 16a assumption)?? If any of this is even close, then I may also just dis-connect the WFCO, actually mount a switch so it could be switched back over.
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offgrid
Senior Member
Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 26 Oct 2019 at 7:06am |
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Normally power electronic devices are specified by their output not their input so in theory the dc/dc converter you're talking about ought to output 20A. It would be the input current that would be higher than 20A.
Wiring losses don't effect current, they result in voltage drops so that shouldn't reduce the output current. The wiring losses show up as a lower voltage at the Li battery terminals than the output voltage limit you set for the converter. I would just use as large a wire gauge as will fit on the converter terminals and try to keep the wire runs short. So, at 20A 4 hours runtime ought to give you 80 amphours. But 4 hours idling your TV to recharge your battery while camping is a long time.
For me the design criteria are to minimize the TV engine idle time by recharging in as short a time as possible while not overloading the alternator. Alts are not good for their nominal rating at idle, it is quite a bit less. I did that test on my Highlander and got about 80A available from a 150A rated alt at idle after electrical demand from the ignition system, engine ecu, and radiator fans was met (all other TV electrical loads off). So, depending on your alt capacity you too probably can run a larger dc/dc converter than 20A to keep your charging times shorter. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Olddawgsrule
Senior Member
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
Posted: 26 Oct 2019 at 7:48am |
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Very good indeed. I expected some efficiency loses.
My daily usage (at max) could be returned in a hour! The worst I hit (2 runs back) was down 700+ watts and it was still rain in our future, for a couple more days. Believe that was over 4 days. We packed up (time to head out anyway) and charged up on the drive (mostly). That's how I usually get recharged, solar or TV. From what I have reading/learning and what you stated of our B to B is direct, it seems beneficial to mount one of these charger units, anyway. I see several can be set for PbA, Gel, Agm or Lithium's.
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offgrid
Senior Member
Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Posted: 26 Oct 2019 at 9:05am |
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OK, sounds good. The benefit of staying under 30A for your dc dc converter feed is that you probably have that capacity already coming through your trailer connector, you'll just need to run that to the converter rather than the 12V battery buss.
For me since I want to run about 80A I'm going to have to install a dedicated high capacity circuit and connectors between the TV and the trailer.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Olddawgsrule
Senior Member
Joined: 20 Sep 2017 Location: New Hampshire Online Status: Offline Posts: 1014 |
Posted: 27 Oct 2019 at 10:55am |
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Here's the basic's I have in mind.
 I'm looking at the Renogy 12/12 20amp charger. For right now I may use my small lithium battery (38ah) or just buy something over the winter in the 60-100ah range. Size will depend mainly on pricing (deal). I am assuming right now that the 7 pin wiring goes all the way to the panel. I do now there is this auto breaker (and buss bar?) located under the Rpod up front. Could this be a location to tap in the 12/12 charger?
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Lithium Battery install ?