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Open Roads Forum  >  Truck Campers

 > Lance TC - lithium - DC-DC charger question

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otrfun

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Posted: 05/19/22 07:26pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

. . . With the truck engine off, if I forget to turn off the DC-DC it still does about 14 amps from the truck battery. Goes back to 20 when the truck is turned on. Oops, it is a Chev, no isolator, I must remember to go back into the camper and turn the DC-DC off. Easy to forget if you stop to go into a store, or worse go off for a longer time.

The DC-DC isolates the truck batt from the camper batt, but it does not isolate the camper from the truck unless you have a Ford. I could put an isolator in the camper somehow as others have--might save me someday.
Can't imagine using our 40a dc2dc charger without a battery isolator or equivalent to automatically take it off-line when the alternator is off-line. For us, just too easy to forget.

As for isolating the 7-pin pos (+), we simply disconnected it inside the 7-pin truck to TC pigtail connector. For us, it serves no useful purpose and is just a liability with the dc2dc charger online. If we did need the pos (+) for some reason, all we have to do is reconnect the pos (+) wire inside the 7-pin pigtail connector.

srschang

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Posted: 05/20/22 05:43am Link  |  Quote  |  Print  |  Notify Moderator

I found this interesting. This is for a 2019 or newer Ram 2500 & 3500 220A alternator which is my truck. The alternator really doesn't produce anything at idle. And it derates the alternator if the air temperature flowing through the alternator gets to 200 deg F.

[image]


2022 Ram 3500 Dually Crewcab Longbed Cummins, 2019 Northstar 12 STC

ticki2

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Posted: 05/20/22 06:28am Link  |  Quote  |  Print  |  Notify Moderator

Considering it’s a diesel it will be running in the lower rpm range further limiting its output


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srschang

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Posted: 05/20/22 07:11am Link  |  Quote  |  Print  |  Notify Moderator

Ah, but I missed this part. The chart above is alternator RPM, not truck RPM.
Apparently my alternator is spinning 3.24 times faster than the engine RPM.

[image]

otrfun

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Posted: 05/20/22 07:24am Link  |  Quote  |  Print  |  Notify Moderator

srschang wrote:

. . . The alternator really doesn't produce anything at idle . . .
Most alternators run at ~3 times engine speed. Our Cummins idles at 700 rpm or 1000-1500 set to high idle. 700-1500 engine rpm would equate to roughly 2100-4500 alternator rpm or 150-200a according to this chart.

orourkmw

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Posted: 05/20/22 08:11am Link  |  Quote  |  Print  |  Notify Moderator

One more question, please. I’ll be wiring up in the next few days. I plan to use the Lance truck plug with 8 ga wires from the truck battery to the camper plug at the front of the camper, which runs to the 30A DC-DC just upstream from the house battery. The other smaller (lights) wires will go to the 4-way pin at the rear of the truck. Since the DC-DC is itself an isolator, and the Lance camper has its own isolator (Blue Seas Battery Link Automatic Charging Relay), will there be any conflict if I leave the wiring through the Blue Seas ACR?

BFL13

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Posted: 05/20/22 10:18am Link  |  Quote  |  Print  |  Notify Moderator

Can't answer about the camper isolator for how it works.

Note IMO you will have trouble keeping the input voltage to the DC-DC up and might want to do the neg input path to truck frame trick later if that happens.

Another factor is that with the Chev, I could plug the camper in at home and that would also maintain the truck battery. Now the converter can't get at the truck battery, so it needs another battery maintainer if parked for very long. Same as a MH in that regard now with the DC-DC in the camper.


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S Davis

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Posted: 05/20/22 10:35am Link  |  Quote  |  Print  |  Notify Moderator

I have pulled 50 amps at idle with my 220 amp alternator every day now for almost a year with no issues.

otrfun

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Posted: 05/20/22 11:09am Link  |  Quote  |  Print  |  Notify Moderator

One of things rarely discussed in these types of discussions is the pre-existing alternator load prior to connecting the dc2dc charger.

On our Cummins (220a alternator; OEM configured, with no optional or additional electrical equipment connected) alternator load can vary from 40a to 70a. Load varies depending on the starter battery SOC and which accessories are in use (lights, a/c, etc.).

It's the remaining load capacity that determines whether a given dc2dc charger can be safely powered by a given alternator. Depending on the pre-existing load, a 160a alternator can potentially handle a given dc2dc charger with more headroom than a 220a alternator.

* This post was edited 05/20/22 11:27am by otrfun *

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Posted: 05/23/22 12:29am Link  |  Quote  |  Print  |  Notify Moderator

JoeChiOhki wrote:

This stuff has gotten so complicated in the last ten years or so.

In the olden days, we just put a 90amp self-resetting marine breaker on the firewall on the line coming back to our 100amp rated Lift Gate Plugs for our charging umbilical between the truck and camper with 4 or 2 gauge wire all the way back and connected to our big banks of batteries.


Hey Matt, that's basically how I used to do it before getting 400 ah of life in the TC. Now it's DC TO DC and no 12 volt direct connection from truck to TC bat bank. You don't want the higher charger voltage feeding back through the 12 volt 7 pin connection creating a loop and throwing off your ecm voltage regulator.


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