Lance TC - lithium - DC-DC charger question

[orourkmw]

I’ve just purchased a 2020 Lance 975 that will sit in my 2022 F350. I have to install the Lance 6-pin at the front of my bed. I will also replace the two 12V lead acid house batteries with one 200 ah LiFePO4. The Lance has a battery separator, which appears to be installed just upstream of the house batteries. I think I need a DC-DC charger to protect the 270A alternator (as well as to get charging benefits), and am considering 30A-40A. Lance specifies at least 8 gauge hot and ground wires from the truck to the 6-pin. I am thinking that to protect the alternator from a large current draw, ideally I should run 2 or 4 AWG wire from the truck battery all the way to the DC-DC, and back, and not connect to the 6-pin plug (so skip the 8 ga). I think CamperJeff explained the potential complications of feeding the 6-pin. I would mount the DC-DC at the battery box, which is ~4 foot from the pin connector, so I’ll have to see how to feed the wire through. My questions are these: First, am I understanding this properly? If I can keep the battery separator in-line and ahead of the DC-DC, can I avoid the D+ signal wire that the DC-DC uses to isolate truck from house? I think the DC-DC only takes as large as 6 ga, so I’ll need to narrow down as close to the end as I can manage. Is there still a risk of overheating when running lighter gauge wire between the relatively short run from the battery isolator through the DC-DC to the LiFePO4? Any guidance would be appreciated.

[orourkmw]

BFL13: what is the size of your “bypass wire” that carries the current to the DC-DC?

[BFL13]

"I've heard of others rewiring from the converter/charger to the batteries with similar results.

Personally, I'm just looking for a 'fail safe' of sorts. If/when it might happen that I'm low on juice and digging the Yamaha out is not convenient,"

Some more notes on our camper set up

Can't carry a gen with the truck camper set up we have, so the DC-DC and truck engine is the gen and charger if solar can't keep up.

For the pos 12v to the DC-DC I by-passed the 7-pin connector that goes into the camper at the front of the truck bed, and have that wire with my by- pass wire added to it with a wire nut going inside the camper to the DC-DC. The wire nut is for when the camper is off the truck have to undo that plus pull the 7-pin. The neg to truck bed also comes off.
Proper connectors you can undo and do up would be better of course.

I have the 20 amp Renogy DC-DC and it does 20 amps to the camper batts according to my battery monitor. Way more amps than the 7-pin ever did.

Left campground with batts at 52% and thanks to DC-DC and some solar, it was 82% on arrival back home for about a two and a half hour drive. Way better than 7-pin!

Another advantage to the DC-DC is you can set the voltage to match the voltage of the solar controller so they add their amps. EG the other day with low batts and no solar in the woods, drove to a place in the open mid-day, and was getting 12.2a solar and 20 from the DC-DC measured one at a time and with both on monitor showed total 30.2 amps

( With the Class C alternator charging is at a lower voltage than its solar is set at, so they do not add all their amps. Eg, if solar is 15 amps by itself and alternator is 25 amps (small alternator in our C) you might see 32 amps instead of 40 )

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.

[jaycocreek]

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

It has,huh..

I just cut the charge wire from the truck to the camper..everything works except it won't charge off the alternator..I charge off of solar...Besides getting complicated,if you buy all the odds and ends and gadgets,it really adds up for lithium...

[JoeChiOhki]

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.

[mbloof]

otrfun wrote:

mbloof wrote:

BFL13 wrote:
Another factor is to keep the input voltage high enough so the DC-DC buck/boost converter can maintain the set output amps and voltage to the camper battery. This is a separate issue from fusing the input side for its wire size, and having the input wire gauge match the input amps.

I think your on the right track here.

For camper applications, we have the wiring of the truck, then the connector(s), pigtail and then the wiring in the camper itself.

I swear my 97 Ford had 18AWG wiring! I tapped the output of the alternator and ran to a solenoid (switched on with the engine running) and 6AWG to ~1' of the 7Pin and then spliced in as large of a AWG wire as I could fit. The ground went from the 7Pin to the trucks frame.

At least Lances have 8AWG wire in their pigtails, a quick look at the wire sizes used in most 7Pin cables is 14AWG. 😞 My NL uses 10AWG to go to the battery.

Lets face it, all wire has resistance and higher currents will create higher voltage drops. Depending on efficiency of the step up charger/converter itself (which BTW 'stepping up' a voltage is difficult to do with anything resembling 'efficient') it could be easily trying to draw 50-60A on the input.

However, given the wiring in the camper itself (and the batteries state of charge) the battery may never see 40A of charge current. For example I recently viewed the charge current at the battery after a 2-day trip that the PD6045Li I have in my NL was providing when I got home. ~19A at the battery. 🙂

Personally I'm debating getting a 20A or 40A model myself. I do know that some of them have a switch/configuration option to operate at 1/2 power. 🙂

- Mark0

NL used 15-20 ft. of 10 gauge wire for the battery to converter run on our 8-11, too. Like you we got less than 20a of charge current from our 45a PD converter. We replaced the 10 gauge with 2/0 (now get a full 45a). Used 2/0 'cause we sometimes quick charge our lifepo4 using both our 45a converter and 40a dc2dc charger at the same time (85a of total charge current). FWIW, we used a 25 ft run of 2 gauge cable from our truck's battery to the 40a dc2dc charger mounted inside the TC. 43.5a alternator/battery load with 40a of charge current.

I've heard of others rewiring from the converter/charger to the batteries with similar results.

Personally, I'm just looking for a 'fail safe' of sorts. If/when it might happen that I'm low on juice and digging the Yamaha out is not convenient, three button presses on the Trucks remote could not be easier. 🙂


- Mark0.

[otrfun]

orourkmw wrote:
What kind of connection did you use on the 2 gauge between the truck and camper.

175a, 2-gauge Anderson-type connectors.

[orourkmw]

What kind of connection did you use on the 2 gauge between the truck and camper.

[otrfun]

mbloof wrote:

BFL13 wrote:
Another factor is to keep the input voltage high enough so the DC-DC buck/boost converter can maintain the set output amps and voltage to the camper battery. This is a separate issue from fusing the input side for its wire size, and having the input wire gauge match the input amps.

I think your on the right track here.

For camper applications, we have the wiring of the truck, then the connector(s), pigtail and then the wiring in the camper itself.

I swear my 97 Ford had 18AWG wiring! I tapped the output of the alternator and ran to a solenoid (switched on with the engine running) and 6AWG to ~1' of the 7Pin and then spliced in as large of a AWG wire as I could fit. The ground went from the 7Pin to the trucks frame.

At least Lances have 8AWG wire in their pigtails, a quick look at the wire sizes used in most 7Pin cables is 14AWG. 😞 My NL uses 10AWG to go to the battery.

Lets face it, all wire has resistance and higher currents will create higher voltage drops. Depending on efficiency of the step up charger/converter itself (which BTW 'stepping up' a voltage is difficult to do with anything resembling 'efficient') it could be easily trying to draw 50-60A on the input.

However, given the wiring in the camper itself (and the batteries state of charge) the battery may never see 40A of charge current. For example I recently viewed the charge current at the battery after a 2-day trip that the PD6045Li I have in my NL was providing when I got home. ~19A at the battery. 🙂

Personally I'm debating getting a 20A or 40A model myself. I do know that some of them have a switch/configuration option to operate at 1/2 power. 🙂

- Mark0

NL used 15-20 ft. of 10 gauge wire for the battery to converter run on our 8-11, too. Like you we got less than 20a of charge current from our 45a PD converter. We replaced the 10 gauge with 2/0 (now get a full 45a). Used 2/0 'cause we sometimes quick charge our lifepo4 using both our 45a converter and 40a dc2dc charger at the same time (85a of total charge current). FWIW, we used a 25 ft run of 2 gauge cable from our truck's battery to the 40a dc2dc charger mounted inside the TC. 43.5a alternator/battery load with 40a of charge current.

[S_Davis]

I use a 50 amp Redarc dc/dc charger on my 2019 Chevy (this system is in the rear of the crew cab) charging a pair of 280ah LifeP04, I ran a set of 1/0 DLO cables from the fuse block on the secondary truck battery to a set of 600amp buss bars in the cab and from the buss bars to a lift gate plug in the bed.

I can either power the plug from the truck alternator( I plan on another dc/dc charger in the camper) or the 560ah battery bank. My truck has a high output alternator, it has the snowplow prep option with a 220amp alternator.

[BFL13]

AFAIK the input should be from the truck battery not from the alternator. Something about protecting the alt in case load cut off for some reason IIRC like BMS might do

[greenno]

When I changed over to Lifepo4 cells from the lead/acid original Interstate battery's I went with the Victron 12/12/18 Isolated DC-DC unit and the #10 wires that were existing for the 12v+ and 12v- worked out fine so I didn't have to rewire anything.

[mbloof]

BFL13 wrote:
Another factor is to keep the input voltage high enough so the DC-DC buck/boost converter can maintain the set output amps and voltage to the camper battery. This is a separate issue from fusing the input side for its wire size, and having the input wire gauge match the input amps.

I think your on the right track here.

For camper applications, we have the wiring of the truck, then the connector(s), pigtail and then the wiring in the camper itself.

I swear my 97 Ford had 18AWG wiring! I tapped the output of the alternator and ran to a solenoid (switched on with the engine running) and 6AWG to ~1' of the 7Pin and then spliced in as large of a AWG wire as I could fit. The ground went from the 7Pin to the trucks frame.

At least Lances have 8AWG wire in their pigtails, a quick look at the wire sizes used in most 7Pin cables is 14AWG. 😞 My NL uses 10AWG to go to the battery.

Lets face it, all wire has resistance and higher currents will create higher voltage drops. Depending on efficiency of the step up charger/converter itself (which BTW 'stepping up' a voltage is difficult to do with anything resembling 'efficient') it could be easily trying to draw 50-60A on the input.

However, given the wiring in the camper itself (and the batteries state of charge) the battery may never see 40A of charge current. For example I recently viewed the charge current at the battery after a 2-day trip that the PD6045Li I have in my NL was providing when I got home. ~19A at the battery. 🙂

Personally I'm debating getting a 20A or 40A model myself. I do know that some of them have a switch/configuration option to operate at 1/2 power. 🙂




- Mark0

[BFL13]

Another factor is to keep the input voltage high enough so the DC-DC buck/boost converter can maintain the set output amps and voltage to the camper battery. This is a separate issue from fusing the input side for its wire size, and having the input wire gauge match the input amps.

To achieve that you have to oversize the input gauge wiring beyond what is required to carry the input amps safely. Eg to maintain 14.7v and constant rated output amps to the camper batt, you want say 13v input, despite the DC-DC boost spec that it says it can do it with input as low as maybe 10v. Not mine anyway! Needs higher input voltage.

One way that worked for my set-up is to run the positive cable as say your 6 AWG, but use the truck frame for the neg input path. it is the total R on the circuit that matters, so going fatter on the neg only helps quite a bit to lower total R.

Some folks run fatter wire for both pos and neg but I have no easy route from the truck engine batt back to the truck bed to go to the camper. However it is easy to connect the neg DC-DC input wire to the truck bed as a short wire run.

I use the 7-pin (6-pin) 12v wire which is way too thin for the pos input to the camper where the DC -DC is, because it already has its route through the truck, but make up for that being too thin with the truck frame being the neg path which is like really fat wire.

I ran some tests and at first using both pos and neg 7-pin wires the DC-DC could not hold its output spec because the input voltage drop was too great. Swapping to the truck frame for the neg input path solved that, just barely, but it does the job now.

Oversizing the input gauge like that also means the Dc-DCdoes not need to pull as many amps from the truck battery and so the alternator.

I do not have an isolator in the Chev, like a Ford has. To turn on the Renogy DC-DC I ran the little B+ wire around to the input pos side with a simple on off switch in that wire. All in the camper. So I turn it on and off manually as needed

[orourkmw]

I consulted a wire gauge chart. A 6 ga wire has an ampacity (so can carry an amp load) of 65 amps, while an 8 ga can carry 50A. (The National Electric Code has a safety factor, so for a 15 ft run they list 8 ga wire for 25-30 amps, 6 ga for 40-50, and 4 ga for 60.) I understand that to mean the 8 ga wire can fail before the 60A fuse….the wire is not protected. My thinking, then, is if I drop down to a 50A fuse on the 8 ga wire there should be minimal risk, and I don’t think there should be any nuisance trips. Sorry to belabor this, but I would rather think it out now. Thanks to everyone for the conversation.

[time2roll]

60a fuse is 20% higher than the maximum draw to avoid nuisance disconnect. Still plenty of protection if there is a short. A 30 amp DC-DC charger can easily pull 45 amps if the input voltage is sagging. 10 volts in 14 volts out = 40% more amps needed + efficiency losses.

Although #8 would seem to be fine for the input side, #10 for the output. Best to mount the DC-DC charger close to the battery that is charging.

No issues with 270 or 240 amp alternator.