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Old 01-13-2022, 02:34 PM   #1
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DC to DC charger question

I will be installing a dc to dc charger shortly, my question is should I disconnect the 7 pin charge line?
If it matters this is the charger
https://www.renogy.com/12v-20a-dc-to...ttery-charger/
Thanks
Tom
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Old 01-13-2022, 02:51 PM   #2
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I'm assuming you have a separate DC plus to use as a charging plus wire, with higher amps, instead of the seven pin plus wire. If you have AGM or flooded batteries, no dc-dc is required, but if you have lithiums, it is better to have a dc-dc charger. The dc-dc charger will have a regulated output based on the type of batteries you have. So yes, disconnect the seven pin hot. No need for two different strategies at the same time. Also, the seven pin hot can be used to signal the dc-dc charger to turn on, provided that that hot is controlled by the tow vehicle key. I think the Renogy uses a separate switched hot to turn on, whereas the Victron Orion uses voltage sensing and needs no separate hot, or switch.
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Old 01-13-2022, 04:24 PM   #3
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Guess I need some education here. I have no idea what this is or what its function is.

Walt
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Old 01-13-2022, 05:52 PM   #4
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Quote:
Originally Posted by Raspy View Post
I'm assuming you have a separate DC plus to use as a charging plus wire, with higher amps, instead of the seven pin plus wire. If you have AGM or flooded batteries, no dc-dc is required, but if you have lithiums, it is better to have a dc-dc charger. The dc-dc charger will have a regulated output based on the type of batteries you have. So yes, disconnect the seven pin hot. No need for two different strategies at the same time. Also, the seven pin hot can be used to signal the dc-dc charger to turn on, provided that that hot is controlled by the tow vehicle key. I think the Renogy uses a separate switched hot to turn on, whereas the Victron Orion uses voltage sensing and needs no separate hot, or switch.
Thank You
Also, I knew the Victron is a better charger but Renogy had a good price
https://www.ebay.com/itm/20355408178...tem2f64c4cbf5:
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Old 01-13-2022, 07:12 PM   #5
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Guess I need some education here. I have no idea what this is or what its function is.

Walt

The DC-DC charger allows one to charge the trailer batteries from the tow vehicle and make up for the long wire runs, match the vehicle charging system to lithium trailer batteries and limit the power taken from the tow vehicle. It can take a lower DC voltage and turn it into a higher voltage, and have a multi-stage charge program. Not always needed for AGMs or flooded batteries, but definitely needed for lithiums. It can also be used to shut off the charging power draw from the tow vehicle without unplugging, in other words, isolate the trailer.
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Old 01-13-2022, 07:32 PM   #6
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I intercepted the 7-pin charge line in the closet and ran 8awg from that to the dc-dc charger. That way my electric jack would continue to work by running off the house battery. More details can be seen in my solar install video here: https://youtu.be/5lzwRLJOBI8
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Old 01-14-2022, 10:09 AM   #7
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I ran a separate line consisting of two 6 gauge wires from my pickup's battery to the charger which is located inside my Scamp 19. I used a Anderson plug to disconnect when the trailer is unhooked. I am using the Victron Orion-TR Smart 12/12V-30A Isolated Charger. Am running the Battleborn 200Ah 12V LiFePO4 Heated Battery Kit – 2 Batteries. My 7 pin battery plug was not disconnected.

The Battleborn battery's built in management system will handle any charging voltage issues.
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Old 01-14-2022, 11:15 AM   #8
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Originally Posted by parmm View Post
I ran a separate line consisting of two 6 gauge wires from my pickup's battery to the charger which is located inside my Scamp 19. I used a Anderson plug to disconnect when the trailer is unhooked. I am using the Victron Orion-TR Smart 12/12V-30A Isolated Charger. Am running the Battleborn 200Ah 12V LiFePO4 Heated Battery Kit – 2 Batteries. My 7 pin battery plug was not disconnected.

The Battleborn battery's built in management system will handle any charging voltage issues.
This is very similar to my setup. I also have a Victron Orion 30A, dc-dc charger, but it is not yet installed. I'm charging by simply plugging in my Anderson plug as needed. A set of #4 wires run from the truck battery, through an 80 amp breaker, and back to the rear bumper, where the Anderson plug is. And then on as #6 wires inside the trailer. I'm also running the power through the on-board shunt to read the amps being delivered.

I have 480 amp hours of lithium, (4) VPR 120 amp hour in parallel. They don't want voltage over 14.6 and I do not want to rely on the internal BMS to limit this, so I wait until the truck charging voltage drops below 14.6, and then plug in. This is a temporary hack, but it works until I install the Victron.

There is a small conflict with this kind of charging. If the solar (460 watt system) is charging when I plug in the truck, the solar charger and Go Power system can think the batteries are fully charged by mis-interpreting the apparent battery voltage. But other than that, charging with an Anderson style system from the truck is a wonderful way to get some serious amps to the batteries. This really helps in extended bad weather and, obviously, works at night. So I can top off the batteries simply by driving to the next location. I've been doing this for the past two years with two different trailers and two different trucks.

The Orion will go in as soon as we get back from this trip. I plan to control it by adjusting its threshold voltage to sense when the truck is running. Is that how you run yours? I see no reason to leave the plus wire from the seven pin connected as it will not provide the same voltage, or even very useful amps as compared to the Orion. Plus, if needed, it could be used as a signal wire for the Orion.
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Old 01-14-2022, 02:14 PM   #9
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Trailer: scamp 13
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Quote:
Originally Posted by parmm View Post
I ran a separate line consisting of two 6 gauge wires from my pickup's battery to the charger which is located inside my Scamp 19. I used a Anderson plug to disconnect when the trailer is unhooked. I am using the Victron Orion-TR Smart 12/12V-30A Isolated Charger. Am running the Battleborn 200Ah 12V LiFePO4 Heated Battery Kit – 2 Batteries. My 7 pin battery plug was not disconnected.

The Battleborn battery's built in management system will handle any charging voltage issues.
Question, rather than run lets say 20ft #6 ground wire from your truck's battery, could one just run a ??ft ground from the input side of the dc charger back to the frame of the truck, since the battery grounds to the frame anyways?
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Old 01-14-2022, 06:59 PM   #10
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Question, rather than run lets say 20ft #6 ground wire from your truck's battery, could one just run a ??ft ground from the input side of the dc charger back to the frame of the truck, since the battery grounds to the frame anyways?
One could do that. It has been suggested. I don't think it is a good idea, but I've never done it. Before you do, compare the resistance of the frame to that of the wire, at let's say, 50 amps, and decide if it makes sense. A 20' piece of steel wire, riveted together, doesn't seem like a good conductor. Running two wires is not that much harder than running one. And the heavy amp draw of the starter, for instance, grounds through the block.
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Old 01-14-2022, 07:35 PM   #11
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There is a small conflict with this kind of charging. If the solar (460 watt system) is charging when I plug in the truck, the solar charger and Go Power system can think the batteries are fully charged by mis-interpreting the apparent battery voltage. .
I know my all Victron setup allows the dc-dc charger to charge from the tow vehicle and the solar controller to charge at the same time. The solar controller gets charge state from the BMV-712 and knows even though it sees the higher voltage, the batteries aren’t fully charged.
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