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Open Roads Forum  >  Truck Campers

 > Lance TC - lithium - DC-DC charger question

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Grit dog

Black Diamond, WA

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Posted: 05/15/22 11:42am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

I sometimes have to just giggle at responses like "next time don't waste your money on the HD alternator...."


The only real question is what charge voltage and how many amps you'll get out of the truck's charging system, depending where you wire the custom plug to, for the 12V hot lead.
Not whether you'll overload the truck's alternator.


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orourkmw

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Posted: 05/15/22 12:02pm Link  |  Quote  |  Print  |  Notify Moderator

Sorry, I had a typo…it is a 240A alternator, and it was a no-charge option. I received the Victron 12-12/30 today. The manual says for a 5 m wire run (approximately what I’ll have from truck battery to camper battery, it should be 6 AWG with a 60A fuse. I just want to double-check if that changes anybody’s guidance. It will be much simpler to run the standard 8AWG to 6-pin, but I don’t want to take undue risk.

3 tons

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Posted: 05/15/22 03:20pm Link  |  Quote  |  Print  |  Notify Moderator

orourkmw wrote:

Sorry, I had a typo…it is a 240A alternator, and it was a no-charge option. I received the Victron 12-12/30 today. The manual says for a 5 m wire run (approximately what I’ll have from truck battery to camper battery, it should be 6 AWG with a 60A fuse. I just want to double-check if that changes anybody’s guidance. It will be much simpler to run the standard 8AWG to 6-pin, but I don’t want to take undue risk.


I’m not a dc2dc user, but it seems kinda odd to me that they would recommend a 60a fuse if it’s only a 30a charge device, thus, I don’t understand the manual’s call for #6…I’m a little lost…

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time2roll

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Posted: 05/15/22 03:32pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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orourkmw

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Posted: 05/15/22 07:29pm Link  |  Quote  |  Print  |  Notify Moderator

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.

BFL13

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Posted: 05/15/22 09:28pm Link  |  Quote  |  Print  |  Notify Moderator

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

* This post was edited 05/15/22 09:37pm by BFL13 *


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mbloof

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Posted: 05/15/22 11:20pm Link  |  Quote  |  Print  |  Notify Moderator

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. [emoticon] 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. [emoticon]

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. [emoticon]




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greenno

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Posted: 05/15/22 11:45pm Link  |  Quote  |  Print  |  Notify Moderator

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.

BFL13

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Posted: 05/16/22 07:40am Link  |  Quote  |  Print  |  Notify Moderator

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

S Davis

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Posted: 05/16/22 11:00am Link  |  Quote  |  Print  |  Notify Moderator

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.

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