DC - DC Charger Project

[Guest]

Yes this was going to be my suggestion, I have no idea if your flooded batteries would take that much for that long (or if it would be good for them, they might boil out) but if you're considering lithium in the life of the rig then it will be worth it.

Neil,

Thinking that with a 30amp (updated) DCDC being distributed to 4-6v battery bank should not be an issue. But it would certainly be best to check with Crown battery. The lithium battery bank is of no concern, where I charge my single 100ah lithium battery at 0.5C (50-55amps).

The Renogy has a switch to cut charge rate in half where if Keith is working to buy a DCDC, and to charge FLA batteries until he switches to Lithium, the Renogy may be the best bet. I am reading that many golf cart chargers are 25amp so a 30 amp Renogy may be the best compromise. A switched 15amp for FLA and the full 30amp for lithium. The charge profiles are also switchable on the Renogy.

https://www.crownbattery.com/news/to...ry-maintenance

Jim

[ncitro]

Keith,

If your running a dedicated power and ground circuit why not get the larger output model? Your FLA batteries will only accept so much but if you switch to lithium they will pull all that power in.

Jim

Yes this was going to be my suggestion, I have no idea if your flooded batteries would take that much for that long (or if it would be good for them, they might boil out) but if you're considering lithium in the life of the rig then it will be worth it.

[Guest]

OK this may sound like a really dumb question at this point, but with all the good options open to me on what to chose and with my bank of 4- 6V 260Ah batterys in series/parallel 520 total AH (260 usable) - How much DC-DC charge power do I REALLY need? I know lots of if's. Lets say overnight I am down to 12.4 volts 70% SOC. Assume 4 to 6 hours of driving, and I have no idea how to adjust for solar 540w - lets assume rainy day...Check my math - .70% SOC means I need to recover 30% of 520 AH or 156 AH or is it 30% of 260AH or 78 AH. Assuming the 30A I would need 5.2 hours driving time for the former and if the latter just 2.6 hours to recover? I am also thinking if I go Lithium in the future I will be in better shape as they charge faster - correct?

I know I am missing something here
Thanks Keith

Keith,

If your running a dedicated power and ground circuit why not get the larger output model? Your FLA batteries will only accept so much but if you switch to lithium they will pull all that power in.

Jim

[Yoda]

OK this may sound like a really dumb question at this point, but with all the good options open to me on what to chose and with my bank of 4- 6V 260Ah batterys in series/parallel 520 total AH (260 usable) - How much DC-DC charge power do I REALLY need? I know lots of if's. Lets say overnight I am down to 12.4 volts 70% SOC. Assume 4 to 6 hours of driving, and I have no idea how to adjust for solar 540w - lets assume rainy day...Check my math - .70% SOC means I need to recover 30% of 520 AH or 156 AH or is it 30% of 260AH or 78 AH. Assuming the 30A I would need 5.2 hours driving time for the former and if the latter just 2.6 hours to recover? I am also thinking if I go Lithium in the future I will be in better shape as they charge faster - correct?

I know I am missing something here
Thanks Keith

[Guest]

Yoda Guest and Jimmer

Forgive the pontification, but I despise the word "ground" when discussing 12vDC. 12v Return or -12vDC is a more apt description because the output from a battery will find it's way back to the battery. Ground is a term that should be used with AC (in this case literally ground as electricity will find it's way back to the power source via the ground if necessary).

The point of the last two sentences is to suggest thinking in terms of minimizing the electrical resistance between the DC-DC Charger and the tow vehicle's battery (or batteries). For the relatively long distance involved from the front of a modern truck to the trailer's battery bank, designing a system with the minimum possible resistance (and accounting for losses) is an important consideration.

Jimmer -- your post states, "...ground from the tow vehicle is connected to the trailer frame,...". Could you expound on how this was done on your setup?

Howard

Howard,

The vehicle OEM drawings are full of references of vehicle grounds where the TV battery is connected to a chassis ground. Most other circuits in the TV are connected to a plethora of chassis grounds where the vehicle chassis is used for the return back to the battery. The same method is used in our trailers.
For AC I believe your referring to an earth ground.

Jim

[Guest]

Jim, you wrote in your post "Otherwise, you will be using the chassis ground on the trailer to handle the high current load in charging your batteries." What's wrong with this? I'd rather have 60 amps running through my truck frame and camper frame than a wire. As long as there is a solid/clean connection to the frame, it will work perfectly. The Victron smart shunt shows that my Renogy 60 amp charger is putting out over 59 amps into the batteries, so it is working as intended.

Jimmer,

"Otherwise, you will be using the chassis ground on the trailer to handle the high current load in charging your batteries. If your adding heavy cabling on the trailer batteries to ground, either unit will work IMO."

Jim


The next line explains that if a heavier ground is added this would not be a problem. The ground I was referring to is the original 6 awg ground wire which would be inadequate IMO for a high current DCDC.

Jim

[Jimmer]

Yoda Guest and Jimmer


Jimmer -- your post states, "...ground from the tow vehicle is connected to the trailer frame,...". Could you expound on how this was done on your setup?

Howard

The negative wire/ground from the tow vehicle goes to the trailer through an Anderson connector. From the Anderson connector on the trailer, I run the black/negative/ground wire to the frame of the trailer through a self tapping bolt (The frame is boxed so I couldn't easily use a nut/bolt). I ground down the paint off of the trailer frame at the point of connection to bare metal. Covered the frame and terminal with NO-OX-ID A-Special- Electrical Contact Grease. I may have used a stainless steel washer, although I can't see it in the picture. When it was all assembled, I painted it black. Did something similar on my truck, but drilled through the truck frame and used a stainless nut and bolt. I don't know how long it will be before corrosion starts to deteriorate the connection, but 4 months after I did it is working perfectly.

[howson]

Yoda Guest and Jimmer

Forgive the pontification, but I despise the word "ground" when discussing 12vDC. 12v Return or -12vDC is a more apt description because the output from a battery will find it's way back to the battery. Ground is a term that should be used with AC (in this case literally ground as electricity will find it's way back to the power source via the ground if necessary).

The point of the last two sentences is to suggest thinking in terms of minimizing the electrical resistance between the DC-DC Charger and the tow vehicle's battery (or batteries). For the relatively long distance involved from the front of a modern truck to the trailer's battery bank, designing a system with the minimum possible resistance (and accounting for losses) is an important consideration.

Jimmer -- your post states, "...ground from the tow vehicle is connected to the trailer frame,...". Could you expound on how this was done on your setup?

Howard

[Jimmer]

Keith,

I struggled with connecting my Renogy with both input and output grounds (4 wire) where after checking with an EE at work, I grounded both input and output to the negative buss bar on the trailer which is grounded to the trailer chassis. Since the trailer battery is grounded to the trailer chassis to operate the rig and the TV is grounded to the trailer chassis in order to operate lighting, I didn't see another way of getting around this. The system works as intended where the positive terminal is isolated from the RV (unless the Renogy is active) but the TV and RV share a ground. If your intending on running dedicated +/- wires from your TV, I would use the 4 terminal unit for a high output unit like a 30amp model. Otherwise, you will be using the chassis ground on the trailer to handle the high current load in charging your batteries. If your adding heavy cabling on the trailer batteries to ground, either unit will work IMO. A confirmation from an electrical guru would be welcome here.

Jim

I have the Renogy 60amp DC-DC charger in my travel trailer. It has worked perfectly since it was installed about 4 months ago. The negative terminal of the batteries in the travel trailer trailer are connected to the trailer frame through a bus bar. The ground from the tow vehicle is connected to the trailer frame. I don't see how how having a common ground for everything could be a problem.

Jim, you wrote in your post "Otherwise, you will be using the chassis ground on the trailer to handle the high current load in charging your batteries." What's wrong with this? I'd rather have 60 amps running through my truck frame and camper frame than a wire. As long as there is a solid/clean connection to the frame, it will work perfectly. The Victron smart shunt shows that my Renogy 60 amp charger is putting out over 59 amps into the batteries, so it is working as intended.

[Guest]

Guest
New question
I see Victron Orion-Tr Smart 12/12-30A DC-DC charger has two models Non-Isolated (3 terminals hot in, ground, hot out) and Isolated (4 terminals +/- in and +/- out with chassis ground. What is the difference and which is better? I am thing that as the only real ground between the truck and trailer is maybe a 12 gauge wire in the cord, I need the isolated so I can bring the negative cable to it.
wygieman
How is you Renolgy 60A holding up. I was reading reviews and folks are having a few random quality issues. Appreciate the input on the alternator, but the 2022 supposedly have something new where it can output more if called for, up to 30A - still reading up and need to verify the wiring.. My new order truck has the instant cab heat so will have the 397 amp alt.

Keith,

I struggled with connecting my Renogy with both input and output grounds (4 wire) where after checking with an EE at work, I grounded both input and output to the negative buss bar on the trailer which is grounded to the trailer chassis. Since the trailer battery is grounded to the trailer chassis to operate the rig and the TV is grounded to the trailer chassis in order to operate lighting, I didn't see another way of getting around this. The system works as intended where the positive terminal is isolated from the RV (unless the Renogy is active) but the TV and RV share a ground. If your intending on running dedicated +/- wires from your TV, I would use the 4 terminal unit for a high output unit like a 30amp model. Otherwise, you will be using the chassis ground on the trailer to handle the high current load in charging your batteries. If your adding heavy cabling on the trailer batteries to ground, either unit will work IMO. A confirmation from an electrical guru would be welcome here.

Jim

[wygieman]

wygieman
How is you Renolgy 60A holding up. I was reading reviews and folks are having a few random quality issues. Appreciate the input on the alternator, but the 2022 supposedly have something new where it can output more if called for, up to 30A - still reading up and need to verify the wiring.. My new order truck has the instant cab heat so will have the 397 amp alt.

My Renogy 60A has worked as specified from installation. I can’t comment on Renogy support as I haven’t needed any. I do switch it between 30A and 60A depending on whether I have discharged batteries to be recharged while driving or if I was plugged in and just want to support the refer for the drive and stay charged up. It would be great if the new trucks can output 30A over the standard umbilical. My truck has dual alternators with plenty of available amps but is limited to ~7A over the standard connection.

Edit to add: Also note that the 30A charger will require more than 30A input to get to the correct charge voltage. In my case, the charger draws over 35A to supply 30A to the batteries at the correct voltage and that is with 4AWG cables. If the truck is fused at 30A, I suspect you are probably close to a 20-25A max charge rate which is, of course, a substantial maintenance charge rate.

[Yoda]

Guest
New question
I see Victron Orion-Tr Smart 12/12-30A DC-DC charger has two models Non-Isolated (3 terminals hot in, ground, hot out) and Isolated (4 terminals +/- in and +/- out with chassis ground. What is the difference and which is better? I am thing that as the only real ground between the truck and trailer is maybe a 12 gauge wire in the cord, I need the isolated so I can bring the negative cable to it.
wygieman
How is you Renolgy 60A holding up. I was reading reviews and folks are having a few random quality issues. Appreciate the input on the alternator, but the 2022 supposedly have something new where it can output more if called for, up to 30A - still reading up and need to verify the wiring.. My new order truck has the instant cab heat so will have the 397 amp alt.

[Guest]

The problem with an isolator is it still has a parallel connection when both batteries are charging, so no dedicated lithium profile if lithium is a consideration. The DC-DC charger is a true isolated connection where the charge profile resides in the DC-DC charger and is independent of the TV charging strategy. Otherwise an isolator is perfect to prevent back-feeding from one battery to another.

Jim

[ncitro]

I'm interested in your setup. Could you expand on your design goals and provide a sketch or basic wiring diagram? Do you have two truck batteries? I assume one of your goals is to keep a your starting battery charging even when the RV battery bank is fully charged. I don't think draining the starting battery has been discussed on this forum before, but it definitely seems problematic to me.

Thanks.

-Steve

I would think I'm the case of lithium RV batteries, draining of the starting battery should be minimal. The resting voltage of the lithium batteries is higher than the lead acid in the truck, so I would not think much current should flow from the actual truck battery to the RV battery. Not 100% on that as I use a DC to DC charger that's fed by a switched ignition source, but I think that's correct.

[steve&renee]

... I'm using the Keyline Iso-Pro 140 battery isolator which is connected to ground through a switch on the dash in my truck. I don't have any solar (yet) so I wanted maximum charging of the 5 Battleborn 100ahour batteries in my RV. I'm very happy with this setup.

I'm interested in your setup. Could you expand on your design goals and provide a sketch or basic wiring diagram? Do you have two truck batteries? I assume one of your goals is to keep a your starting battery charging even when the RV battery bank is fully charged. I don't think draining the starting battery has been discussed on this forum before, but it definitely seems problematic to me.

Thanks.

-Steve