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mikeywhatwhat Samba Member
Joined: June 23, 2017 Posts: 16 Location: Los Angeles
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Posted: Wed Aug 05, 2020 2:24 pm Post subject: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Hey everyone. I think I am approaching my final design for the aux battery system and was hoping for you experienced folks to look this over and make sure I am not doing anything completely stupid. Any/all criticism welcome. I am trying to keep it simple and spending a bit more money hoping that I only need to do this once in the vans life.
Question I have:
1. Does this diagram seem to make sense? Would this work..?
2. Do I need a relay between the solar/starter battery and the BCDC1225D? See below diagram from Redarc site. I thought the Redarc just needed the solar and starter battery connected and it was smart enough to handle the rest.
3. I assume I need a fuse between the aux battery and the stock fuse box for fuse #3. What size fuse would this need to be?
4. I assume I need a fuse between the solar panel and the Redarc. Would that be a 30amp inline fuse?
Thanks so much!
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Westified Samba Member
Joined: May 01, 2012 Posts: 409 Location: Miami, FL
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Posted: Wed Aug 05, 2020 3:06 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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I believe you can add a positive wire from your shunt to the red wire (positive) from the Redarc that goes to the starting battery (positive). This way you can monitor both batteries with the BMV 712 Victron. Not sure about your relay between the solar and starting battery. The diagram I see in their manual is Lithium specific. You must have an unregulated solar panel. Google their manual and look at figure 2.7.2 on page 11. The Vanagon does not have a smart alternator so you shouldn't need the blue wire to the ignition, unless you installed a smart alternator. Also, I would probably use a little heavier gauge to the solar panel and fuse it. _________________ 1984 Westy Wolfsburg, owned since 1987. FAS 2.0 NA engine conversion in 2022. |
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Westified Samba Member
Joined: May 01, 2012 Posts: 409 Location: Miami, FL
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Posted: Wed Aug 05, 2020 3:29 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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This is a diagram of my proposed install of the Redarc BCDC 1225D, Victron battery charger IP65, Victron BMV 712 monitor with shunt. Hopefully it is correct. I am just beginning my install, the parts have arrived.
_________________ 1984 Westy Wolfsburg, owned since 1987. FAS 2.0 NA engine conversion in 2022. |
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spunky goat Samba Member
Joined: July 06, 2014 Posts: 9 Location: Minneapolis, MN
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Posted: Wed Aug 05, 2020 3:40 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Westified - Will the Redarc allow current to flow from the Aux battery to the Starter battery when plugged into shore power?
I am considering a similar set-up and have the same Victron IP65 charger as you and wondering if DC-DC chargers allow current to flow from aux to starter battery. |
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mikeywhatwhat Samba Member
Joined: June 23, 2017 Posts: 16 Location: Los Angeles
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Posted: Wed Aug 05, 2020 4:32 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Posting the diagram Westified mentioned here. This doesn't look like the relay is required but also doesn't show the solar panel fused to the Redarc directly. I suppose a fuse could never hurt though, right?
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Westified Samba Member
Joined: May 01, 2012 Posts: 409 Location: Miami, FL
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Posted: Wed Aug 05, 2020 7:57 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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spunky goat wrote: |
Westified - Will the Redarc allow current to flow from the Aux battery to the Starter battery when plugged into shore power?
I am considering a similar set-up and have the same Victron IP65 charger as you and wondering if DC-DC chargers allow current to flow from aux to starter battery. |
I purchased my Redarc from Ken at Vanagain. He said yes, you can hook up the charger and it will charge both the starting battery and the auxiliary battery. Current is not flowing from the Auxiliary battery to the Starter Batttery. It is flowing to the Starting Battery and the Redarc DC to DC charger. In the wiring diagram I posted you can see the red wire from the charger tapping into the red wire of the Redarc. That red wire is also connected to the Starting Battery. Therefore, when you charge the via the charger it charges both batteries. The Redarc thinks it is the alternator and passes the correct charge profile to the Lithium battery. I talked with BattleBorn who I purchased the battery and charger from and they said, set the charge profile on the charger to flooded lead acid. This will be correct for the Starting Battery and then the Redarc will give the correct charge to the lithium if you setup the Redarc for Lithium. That is my plan. Hope this answers your question. _________________ 1984 Westy Wolfsburg, owned since 1987. FAS 2.0 NA engine conversion in 2022. |
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Westified Samba Member
Joined: May 01, 2012 Posts: 409 Location: Miami, FL
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Posted: Wed Aug 05, 2020 8:10 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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mikeywhatwhat wrote: |
Posting the diagram Westified mentioned here. This doesn't look like the relay is required but also doesn't show the solar panel fused to the Redarc directly. I suppose a fuse could never hurt though, right?
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You are correct it does not show the relay. I don't believe you need it. You need to determine if you have smart alternator or not. If you have the stock alternator then it is a standard alternator. The manual tells you how to setup the Redarc if you have a standard or smart alternator (variable voltage). Regarding fusing the solar panel, I was going to do this just for added safety. Redarc does not say you need to fuse the panel. Good luck with your install. _________________ 1984 Westy Wolfsburg, owned since 1987. FAS 2.0 NA engine conversion in 2022. |
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mikeywhatwhat Samba Member
Joined: June 23, 2017 Posts: 16 Location: Los Angeles
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Posted: Fri Aug 07, 2020 4:24 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Follow up on the need for a Relay-
Per the Redarc installation guidelines, a relay will NOT be required. It seems the older version of the BCDC1225D would require a relay, so there's some outdated information out there (Youtube install video, old manuals), but I can confirm through Redarc that with the current BCDC1225D you do NOT need a relay if you are using solar and alternate charging. |
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puchfinnland Samba Member

Joined: December 26, 2005 Posts: 292 Location: Deale Maryland
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Posted: Sat Aug 08, 2020 6:30 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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I assisted Ken with the initial testing of the redarc on the Vanagons, I am currently working on installing a redarc with a 12v relay and an AC battery charger.
I chose this relay-
https://www.amazon.com/gp/product/B08BHNYQYY
its 5 pole, so the input can be switched
my charger is a dual output
one leg goes to the start battery, the other to this relay
IGN off the second leg is in the N/C position-which feeds the redarc
IGN on, the relay switched from AC battery charger to start battey input,
this isolates both legs of the AC charger to work independently
the relay is powered on to connect and isolate the ac charger.
its idiot proof _________________ ABYC marine master technician , EX European auto technician, new business- EASTCOASTWEST , custom work on campers, only systems, no mechanical |
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Arne@kleinersyncro Samba Member

Joined: May 04, 2011 Posts: 73 Location: Australia VIC
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Posted: Sun Aug 09, 2020 12:26 am Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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mikeywhatwhat wrote: |
Follow up on the need for a Relay-
Per the Redarc installation guidelines, a relay will NOT be required. It seems the older version of the BCDC1225D would require a relay, so there's some outdated information out there (Youtube install video, old manuals), but I can confirm through Redarc that with the current BCDC1225D you do NOT need a relay if you are using solar and alternate charging. |
Hey mate,
The old version is the BCDC1225, which has got no Lifepo4 charging program btw, needs the relay if using Solar.
The new version is the BCDC1225D. No need for a solar here. Just installed the BCDC1240D the other week in my van with a 120ah Lifepo4.
Cheers Arne _________________ 1991 Syncro self made camper van, cruising around the Black Forrest area (Germany)
1990 Syncro converted by Camperize NSW, cruising around Australia |
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howler9 Samba Member
Joined: April 12, 2012 Posts: 30 Location: United States
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Posted: Fri Apr 02, 2021 2:00 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Westified wrote: |
This is a diagram of my proposed install of the Redarc BCDC 1225D, Victron battery charger IP65, Victron BMV 712 monitor with shunt. Hopefully it is correct. I am just beginning my install, the parts have arrived.
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Hi Westified, how did your setup end up? It looks the same thing that I am doing very soon. Any pointers? Where did you fit your components? What gauge wires did you use? |
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Reckless Amateur Samba Member
Joined: March 16, 2009 Posts: 224 Location: Philadelphia, PA
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Posted: Mon May 26, 2025 2:48 pm Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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I spent all day wrestling with the Redarc Lifepo2 install. Don't get me started with all the stupid mistakes I made.
I have a lingering question, though. Two actually:
1. What is the thing shown on the Redarc diagram that says low voltage disconnect?
2. More important, if I'm simply trying to connect my Truck Fridge to the Lifepo4, I just run the positive wire (fused) from the fridge to the positive terminal on the battery and the black wire to ground, correct?
Sorry for the stupid questions. Had a long day, a big trip coming up, it's been awhile since I messed with my wiring, my skills are basic, and I'm tired. Time for a beer, but hoping somebody can help me out. Thanks, folks.
David _________________ 91 Bostig-powered Westy (automatic)
Philadelphia, PA |
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Westified Samba Member
Joined: May 01, 2012 Posts: 409 Location: Miami, FL
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Posted: Tue May 27, 2025 7:14 am Post subject: Re: Aux Battery Wiring Diagram questions Redarc 1225D and Lifepo4 |
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Reckless Amateur wrote: |
I spent all day wrestling with the Redarc Lifepo2 install. Don't get me started with all the stupid mistakes I made.
I have a lingering question, though. Two actually:
1. What is the thing shown on the Redarc diagram that says low voltage disconnect?
2. More important, if I'm simply trying to connect my Truck Fridge to the Lifepo4, I just run the positive wire (fused) from the fridge to the positive terminal on the battery and the black wire to ground, correct?
Sorry for the stupid questions. Had a long day, a big trip coming up, it's been awhile since I messed with my wiring, my skills are basic, and I'm tired. Time for a beer, but hoping somebody can help me out. Thanks, folks.
David |
I Installed a Blue Seas fuse panel from West Marine in the cabinet under the sink (refer to my diagram) which I connect to my BattleBorn battery under the drivers seat, I fuse the wire from the Lithium battery to this panel with a 40 amp fuse. I then connect all accessories to this fuse panel, including a fridge if you have one. This way if something shorts out you can easily find the fuse. Label each fuse on the panel (they give you labels).
My understanding of the low voltage disconnect is to connect to the ignition so when the van is on the redarc turns on. I guess if the voltage drops to low it disconnects, did not use this wire. I bought my Redarc from Van-Again who was very helpful with this install. I highly recommend purchasing from him. He said ignore the wire unless you have a Subaru conversion that uses a variable voltage alternator. On a stock vanagon it does not have this. If you have an engine conversion, you must determine if it is a variable voltage alternator.
I have had my Redarc for several years and it works great. Also, Redarc has great support. You can call them and they will answer. Their USA number is (704) 247-5150. That is the one I used. Not sure it is still correct. Their email is [email protected].
I was very careful with my install, since I did not want to burn my van down. I fused everything. Good Luck
Brad
PS I did change my install from the diagram I show. I put an 85 amp battery isolator from the starting battery to the Redarc. From talking to Redarc this is very important because the lithium battery will take all the power up to 25 amps (in my case) it can get, draining your starting battery when you switch the ignition off, thereby killing your starting battery if the lithium is not up to a 95% charge. This has worked great. You can monitor the lights on the Redarc to see when it cuts off. _________________ 1984 Westy Wolfsburg, owned since 1987. FAS 2.0 NA engine conversion in 2022. |
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