Wiring up a DC-DC Charger - Feedback?

[0rion]

I posed a question back in February about using a DC-DC charger in a 'creative' way - as a way of taking the power from the stock WFCO-8955 converter and 'converting' it through the DC-DC charger to better charge a Lithium battery.

I put that project on the back burner, and have since installed my LiFePo4 battery in a spot about 6ft from the converter - I connected the Lithium to the spare positive input lug on the DC Fuse panel and it works great. I was planning to be content with the 80-90% charge the WFCO converter can provide and occasionally top-up with my solar.

However, my Durango doesn't have a shut-off relay for the umbilical when it's not running, so I'd need to babysit my 7-pin connector - which has me considering the DC-DC again. I've also found other users who have set up a DC-DC Charger in the creative way I was thinking, so it's possible. Here's what I'm planning, looking for any constructive feedback:

1. Disconnect the power lead from the umbilical in the j-box, connect it to an auto-reset breaker. Run separate 6 or 8awg from there to the back of the converter (perhaps run separate lines directly to the truck's battery, in the future).
2. On the DC Fuse panel, remove the red wire from the VCC+ Lug. This is the charge wire from the converter.
3. Connect the red converter wire and the umbilical power wire together, run another wire to the input of the DC-DC charger. They should share a common ground. Output of DC-DC goes through a fuse to the Lithium battery.

This way, when I'm plugged into shore power, the power from the WFCO gets cleaned up nicely for the Lithium. When I'm connected to the truck, I get all the advantages the DC-DC charger provides. If both are plugged in, it's really no different than when it was all going through the DC Fuse panel.

Aside from constructive feedback, I'm wondering which type of connector would be recommended for the three 8awg and 6awg wires at the converter? I'd need something besides a wire nut that could protect these positive connections, but something that wouldn't damage the red converter wire, in case I need to reconnect it to the VCC+. Thanks!

[TitanMike]

Originally Posted by 0rion

I posed a question back in February about using a DC-DC charger in a 'creative' way - as a way of taking the power from the stock WFCO-8955 converter and 'converting' it through the DC-DC charger to better charge a Lithium battery.

I put that project on the back burner, and have since installed my LiFePo4 battery in a spot about 6ft from the converter - I connected the Lithium to the spare positive input lug on the DC Fuse panel and it works great. I was planning to be content with the 80-90% charge the WFCO converter can provide and occasionally top-up with my solar.

However, my Durango doesn't have a shut-off relay for the umbilical when it's not running, so I'd need to babysit my 7-pin connector - which has me considering the DC-DC again. I've also found other users who have set up a DC-DC Charger in the creative way I was thinking, so it's possible. Here's what I'm planning, looking for any constructive feedback:

1. Disconnect the power lead from the umbilical in the j-box, connect it to an auto-reset breaker. Run separate 6 or 8awg from there to the back of the converter (perhaps run separate lines directly to the truck's battery, in the future).
2. On the DC Fuse panel, remove the red wire from the VCC+ Lug. This is the charge wire from the converter.
3. Connect the red converter wire and the umbilical power wire together, run another wire to the input of the DC-DC charger. They should share a common ground. Output of DC-DC goes through a fuse to the Lithium battery.

This way, when I'm plugged into shore power, the power from the WFCO gets cleaned up nicely for the Lithium. When I'm connected to the truck, I get all the advantages the DC-DC charger provides. If both are plugged in, it's really no different than when it was all going through the DC Fuse panel.

Aside from constructive feedback, I'm wondering which type of connector would be recommended for the three 8awg and 6awg wires at the converter? I'd need something besides a wire nut that could protect these positive connections, but something that wouldn't damage the red converter wire, in case I need to reconnect it to the VCC+. Thanks!

As for the connectors where multiple wires come together, I wouldn't even consider wire nuts. Best way to hoin all these wires would be either as bus bar With individual connections for each wire or a single terminal/transition post where all wires are connected to a single post. In both cases each wire should be terminated with an appropriately sized, crimped, ring type connector.

These are available on Amazon and are common in the marine world.
Look for bus bars or terminal posts.

[CHICKDOE]

i'll make a couple of comments. take them for what they are worth.

i think you have a 55 amp converter. what capacity dc to dc charger are you going to install. if it's capacity is less than the 55 amp converter it will become the limiting factor in recharged the battery via the converter. so i'm assuming you are going to get a dc to dc charger with as much capacity as possible.

now with a higher capacity dc to dc charger it will try to take as much current as it can from the truck alternator. actual capacity sent back to the dc to dc charger will be limited by the charge wire size. but if it allows a significantly larger current to flow, will that affect the alternator?

i have read that some converters periodically stop the charge current in order to sense the battery voltage. they do this do determine what mode the converter is to operate at (bulk, absorption, float). with the dc to dc charger in line between the battery and the converter how will this affect the converter's ability to sense the battery?

i installed a dc to dc charger in our trailer. in doing so i disabled the emergency break away function. i did not realize this at the time i did the install. the original trailer wiring had the charge line running from the battery positive terminal up to the junction box where the 7-pin cable attaches. also near this box is the break away switch. the trailer charge line connects to the 7-pin cable and a wire to the break away switch. the positive wire to the brakes also terminates in this junction box and connects to the 7-pin brake cable and the other side of the break away switch. this allows charge current coming down the 7-pin cable charge line to reach the battery positive terminal. but should the break away switch get pulled current from the battery can flow up the trailer charge line to the break away switch, through the break away switch, and then down the positive brake wire to activate the brakes. by putting the dc to dc charger in the trailer charge line i interrupted the current flow when the break away switch is pulled.

i'm not saying to do your project or not. i'm just throwing out some issues that may or may not apply.

[TitanMike]

Originally Posted by CHICKDOE

i'll make a couple of comments. take them for what they are worth.

i think you have a 55 amp converter. what capacity dc to dc charger are you going to install. if it's capacity is less than the 55 amp converter it will become the limiting factor in recharged the battery via the converter. so i'm assuming you are going to get a dc to dc charger with as much capacity as possible.

now with a higher capacity dc to dc charger it will try to take as much current as it can from the truck alternator. actual capacity sent back to the dc to dc charger will be limited by the charge wire size. but if it allows a significantly larger current to flow, will that affect the alternator?

i have read that some converters periodically stop the charge current in order to sense the battery voltage. they do this do determine what mode the converter is to operate at (bulk, absorption, float). with the dc to dc charger in line between the battery and the converter how will this affect the converter's ability to sense the battery?

i installed a dc to dc charger in our trailer. in doing so i disabled the emergency break away function. i did not realize this at the time i did the install. the original trailer wiring had the charge line running from the battery positive terminal up to the junction box where the 7-pin cable attaches. also near this box is the break away switch. the trailer charge line connects to the 7-pin cable and a wire to the break away switch. the positive wire to the brakes also terminates in this junction box and connects to the 7-pin brake cable and the other side of the break away switch. this allows charge current coming down the 7-pin cable charge line to reach the battery positive terminal. but should the break away switch get pulled current from the battery can flow up the trailer charge line to the break away switch, through the break away switch, and then down the positive brake wire to activate the brakes. by putting the dc to dc charger in the trailer charge line i interrupted the current flow when the break away switch is pulled.

i'm not saying to do your project or not. i'm just throwing out some issues that may or may not apply.

On the breakaway switch issue, if it was wired so disconnecting the charge wire from 7-pin cable rendered it inoperable, it was wired wrong. The breakaway switch should be wired to a permanent source of trailer battery power.

If a "breakaway" were to occur it's logical the 7-wire cable could well be pulled out as well. On my TT the breakaway switch is connected to the battery side of the battery disconnect switch.

The other wire from breakaway switch went into junction box and joined brake wire from axles and brake activation wire from 7-wire cable.

[CHICKDOE]

the original current path for the break away function was from the battery positive up the trailer charge wire to where it is connected to both the incoming charge line from the 7-pin cable and one side of the breakaway switch. the other side of the break away switch is connected to both the positive wire going to the brakes and the incoming brake line from the 7-pin cable.

in normal operation this allows the 7-pin charge cable to charge the trailer batteries and the 7-pin brake cable to operate the brakes. since the breakaway switch is open these two function operate independently.

but when the break away switch gets pulled (closed) current is able to flow up the trailer charge line from the trailer battery to the one side of the break away switch and then down the trailer brake line to the brakes.

to install the dc to dc charger you cut the trailer charge line and insert the dc dc charge where you made the cut. my point was that installing the dc to dc charger in the trailer charge line interrupts the current flow when the break away switch is pulled as current does not flow backwards through the dc to dc charger.

[0rion]

Originally Posted by TitanMike

As for the connectors where multiple wires come together, I wouldn't even consider wire nuts. Best way to hoin all these wires would be either as bus bar With individual connections for each wire or a single terminal/transition post where all wires are connected to a single post. In both cases each wire should be terminated with an appropriately sized, crimped, ring type connector.

I'd like to be able to put the converter wire back if needed, if I crimp a lug on then I'd need to cut it off and strip a new section of wire if I need to connect it back to the DC fuse board. Not sure if there's that much copper to spare.
Any reason why an insulated multitap connector wouldn't work?

[0rion]

Originally Posted by CHICKDOE

i think you have a 55 amp converter. what capacity dc to dc charger are you going to install. if it's capacity is less than the 55 amp converter it will become the limiting factor in recharged the battery via the converter. so i'm assuming you are going to get a dc to dc charger with as much capacity as possible.

now with a higher capacity dc to dc charger it will try to take as much current as it can from the truck alternator. actual capacity sent back to the dc to dc charger will be limited by the charge wire size. but if it allows a significantly larger current to flow, will that affect the alternator?

i have read that some converters periodically stop the charge current in order to sense the battery voltage. they do this do determine what mode the converter is to operate at (bulk, absorption, float). with the dc to dc charger in line between the battery and the converter how will this affect the converter's ability to sense the battery?

As it is with my Lithium battery wired up 6ft away from the converter, I was pulling around 40amps max from the WFCO so I'd buy my DC-DC accordingly.

As for the truck I wouldn't be changing anything in the vehicle or the trailer's 7-pin cable, only at the junction box. I suppose that some wire resistance may be bypassed by running the 6ga wire from this point straight to the DC-DC charger, but I was only seeing a max of 12-15 amps from the truck while driving - do you think the bypass direct to the DC-DC would pull much more?

Interesting point on the WFCO pausing to check the state of charge - first I've heard of it. I'll need to look into it, but it doesn't sound like something others who've set their DC-DC chargers up like this have worried about.

[01tundra]

Our GMC 2500HD was wired to keep the 12V+ wire in the 7-way hot all the time as well.

Prior to installing our Victron Orion Smart 12/12-18 DC-DC charger I simply put a switch in the trailer that would break the 12V+ lead from the 7-way.

I wired it into the trailer's junction box up front and would typically just leave the switch turned off. That way if the trailer batteries were dead for some reason and I needed to operate the tongue jack or slide, I could turn the switch on and use the tow vehicle battery.

As for connection points, I'd recommend using Blue Sea power posts and terminate the wires with lugs.

This is what I've used throughout our trailer -

https://www.amazon.com/Blue-Sea-Syst...7476613&sr=8-3

https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[hobienick]

You can buy and install a relay in the TV that will disconnect the 7pin charging wire when the ignition is off. I did this on my wife's SUV when we had the pop-up.

[Larry-NC]

Originally Posted by 0rion

Aside from constructive feedback, I'm wondering which type of connector would be recommended for the three 8awg and 6awg wires at the converter? I'd need something besides a wire nut that could protect these positive connections, but something that wouldn't damage the red converter wire, in case I need to reconnect it to the VCC+. Thanks!

Split bolt connectors. Just wrap them with electrical tape after tightening.

If you have three or four, to be connected together, maybe a bus bar with two split bolts in it.

[Tom48]

At a minimum you need to put an isolator on the 12 volt feed through your seven pin. I'm not even a fan of that because the lithium batteries can suck a whole lot of current from your alternator if you're not careful. I'd say if you're going to mess with a DC to DC charge controller do it once and do it right here's a link I happen to see on TV when I woke up this morning and it's pretty good and pretty thorough.. https://youtu.be/ww_4yhQPGwY

[TitanMike]

Originally Posted by Tom48

At a minimum you need to put an isolator on the 12 volt feed through your seven pin. I'm not even a fan of that because the lithium batteries can suck a whole lot of current from your alternator if you're not careful. I'd say if you're going to mess with a DC to DC charge controller do it once and do it right here's a link I happen to see on TV when I woke up this morning and it's pretty good and pretty thorough.. https://youtu.be/ww_4yhQPGwY

A DC-DC charger is an isolator. When D+ lead is at zero volts NO current can flow back out of batteries.

In reality, leaving charge wire connected will allow converter to charge starting battery too with no issues from the Lithium batteries.

[0rion]

For those of you who have run a dedicated line from the TV battery to the trailer to connect to a DC-DC charger, what do y'all do with the trailer's existing 7-pin power line? Is it simply connected to the direct dedicated DC-DC circuit, or do you just leave it as factory, connected to the DC fuse panel?

[01tundra]

Originally Posted by 0rion

For those of you who have run a dedicated line from the TV battery to the trailer to connect to a DC-DC charger, what do y'all do with the trailer's existing 7-pin power line? Is it simply connected to the direct dedicated DC-DC circuit, or do you just leave it as factory, connected to the DC fuse panel?

Ours is still connected, but only powers the TPMS signal booster.

[TitanMike]

I use mine to turn on/off DC-DC charger and power TPMS repeater.

Not connected to anything else.