DC - DC Charger Project

[TedS]

There has to be enough voltage left after the power consuming load to be able to push all that current back to the battery. The voltage required to push the current back to the battery affects the voltage drop across the load, therefore the power available to the load. Considering resistance in the return path would favor a direct wire connection instead of depending on clean chassis/hitch connections for the current return.

[Yoda]

Keith,

Using the Ampacity chart I would use the critical voltage drop scale and determine the cable size based on the maximum output that your Multiplus is capable of inside the rig. Properly delivered voltage to equalize FLA batteries or to balance Lithium batteries is important. So I would wire this with 0awg taking into consideration of the critical voltage drop and to set this up to handle up to 90 amp for when you move to lithium for the TV side.
Initially I was concerned your charge rate would be at 0.1C but if your capable of 0.2C then the 60amp Renogy would work very well and can handle both battery types via dip switches.

Copper wire is crazy expensive right now. Recent home wiring projects just cost me plenty.

Jim

Jim
The multiplus is wired in with 4/0 with 2/0 going to each battery bank.

The wiring I am referring to here is from the Truck Battery (both + and -) to the 60A Renogy DC-DC unit mounted in the front bay of the 5th wheel. 30'-40' one way. Most folks have used 4 awg, but I remember someone using 2 awg. Trying to decided, but thinking 2 awg.
Keith

[Guest]

Jim
The multiplus is wired in with 4/0 with 2/0 going to each battery bank.

The wiring I am referring to here is from the Truck Battery (both + and -) to the 60A Renogy DC-DC unit mounted in the front bay of the 5th wheel. 30'-40' one way. Most folks have used 4 awg, but I remember someone using 2 awg. Trying to decided, but thinking 2 awg.
Keith

Keith,

I would use 2awg. As stated 2/0 for the multiplus.

Jim

[ncitro]

Yoda I ran 4AWG, but I have great 40 amp version. I was occasionally tripping my 60 amp breaker so I replaced it with 80 and it’s been fine since. I agree with the above, voltage drop shouldn’t tacit be an issue as long as your wire has the extra current capacity. That said though I’d probably still use 2AWG, would be a little more overhead and alternator will not work as hard (I know like mine yours has plenty of capacity but better to not stress it).

[Yoda]

Update
I just ordered the Renogy 60A model from Renogy with coupons $195. So now to get the wiring and Anderson connectors. I have also ordered the bulkhead fitting from Australia.

The plan is slowly coming together.
Keith

On edit
Dang I wish I understood the electrical charts more. Blue Sea says I need 2 awg and possible larger. This site for ampacity says I can get away with 4 awg if I stay under 50' in fact ti says 4 awg can handle 100A https://www.directwire.com/resources...mpacity-chart/

So what size wire should I get? Me thinks I should go back to my corner and bang my head on the wall

Keith

[TedS]

Yoda capacity to carry and safe to carry are different animals.

AMPACITY: Welding cable ampacity (also known as current-carrying capacity or current rating) refers to the maximum amount of current (in amperes) that a cable conductor can continuously and safely carry without exceeding the operating temperature rating.

Max temp rating on the welding cable from the sire you referenced is 105 C. That's mighty hot. Go to the larger size so as not to overheat the cables. Go by the voltage drop charts.

[Jimmer]

I used 2 gauge for my 60 amp Dc-DC charger. But 4 gauge will not get overheated. It will have a bigger voltage drop from the truck to charger, but not a big deal as the DC DC charger will output the correct voltage at full amps. It just means that your alternator will have to work a little harder to make up for the heat generated in the wire.

[TedS]

Interesting description installing dc-dc charger in a TT.

https://senormisterioso-wordpress-co...vel-trailer%2F

[Guest]

I'm not an electrician but feel the chassis ground method as described in the article on the TV should be avoided. If the heavy ground cabling fails, the current will take the next best path to the ground wire in the 7 way connector and with a 60amp DCDC this could be an issue. As much as copper costs these days, I would still run a dedicated positive and negative cable from the TV battery to the DCDC. Its important to pull from the battery since many TV applications use a current meter to determine actual SOC and load of the TV battery.

Jim

[TedS]

I agree with dedicated wire for the negative connection. I would not want to depend on the relatively loose hitch pin connection for the return path, tt or 5th wheel, to carry 40 to 60 amps.

[gbkims]

I have 2 Awg Red & Black running back to the truck bed SB120. If I installed a DC-DC in the rig, I'd then run 4 Awg back to the rig since it'd be easier run from the pin box into the rig.

[Yoda]

Yoda capacity to carry and safe to carry are different animals.

AMPACITY: Welding cable ampacity (also known as current-carrying capacity or current rating) refers to the maximum amount of current (in amperes) that a cable conductor can continuously and safely carry without exceeding the operating temperature rating.

Max temp rating on the welding cable from the sire you referenced is 105 C. That's mighty hot. Go to the larger size so as not to overheat the cables. Go by the voltage drop charts.

gbkims Guest
Thanks Ted
I knew I was missing something. I agree 105C is a bit on the hot side. Ill go with the 2 awg. I need that to order the Anderson connectors 120 series and the pins which come separate for the wire size. The sales are wacky this year - need to be careful. Renogy changed thier web pricing back to full msrp with 15% at checkout. A few days ago It was showing the 15% discounted price on the web page, At lease the coupon ( RENOGYSOLAR10) I mentioned in the black Friday thread still worked on top (Entered at checkout) so 25% off all together.

I plan to use an up fitter switch to power the big solenoid that folks have used, https://www.amazon.com/gp/product/B0...WN6HRL8BC&th=1 Is this the correct one?

Then have the Renogy itself activated by trailer running lights. I was going to have 2 blue sea circuit breakers in the lines too (one truck side at battery 100A), and one 5th wheel side after the renogy (70A). Is my sizing and thinking correct?
https://www.amazon.com/Blue-Sea-Syst...T_BREAKER&th=1

Am I missing anything - yep terminal lugs - my Temco crimper comes in handy again

On last question - wire length

I dont have a truck to measure, but for my new F350 cc long bed I'm guessing it's about 23' tip to tail based on my old one, but running from the passenger side where the up fitter switcher are , down and crossing over to the plug location makes that about 30' of cable needed. Then to the trailer, including umbilical is another 12' - 15'. I plan to try and follow the current cable run. That's how I fished my reverse light wire.

So is 50' of black and 50' of red enough? I don't want to end up short.

Thanks everyone for the help

Happy Thanksgiving
Keith

[ncitro]

gbkims Guest
Thanks Ted
I knew I was missing something. I agree 105C is a bit on the hot side. Ill go with the 2 awg. I need that to order the Anderson connectors 120 series and the pins which come separate for the wire size. The sales are wacky this year - need to be careful. Renogy changed thier web pricing back to full msrp with 15% at checkout. A few days ago It was showing the 15% discounted price on the web page, At lease the coupon ( RENOGYSOLAR10) I mentioned in the black Friday thread still worked on top (Entered at checkout) so 25% off all together.

I plan to use an up fitter switch to power the big solenoid that folks have used, https://www.amazon.com/gp/product/B0...WN6HRL8BC&th=1 Is this the correct one?

Then have the Renogy itself activated by trailer running lights. I was going to have 2 blue sea circuit breakers in the lines too (one truck side at battery 100A), and one 5th wheel side after the renogy (70A). Is my sizing and thinking correct?
https://www.amazon.com/Blue-Sea-Syst...T_BREAKER&th=1

Am I missing anything - yep terminal lugs - my Temco crimper comes in handy again

On last question - wire length

I dont have a truck to measure, but for my new F350 cc long bed I'm guessing it's about 23' tip to tail based on my old one, but running from the passenger side where the up fitter switcher are , down and crossing over to the plug location makes that about 30' of cable needed. Then to the trailer, including umbilical is another 12' - 15'. I plan to try and follow the current cable run. That's how I fished my reverse light wire.

So is 50' of black and 50' of red enough? I don't want to end up short.

Thanks everyone for the help

Happy Thanksgiving
Keith

I'd think 50' should be enough. I think I started with 40 and was short. It's not too bad to come up a little short because you need a sister l separate piece for the trailer end anyway. I kept the scrap and used it later to make up a set of booster cables that plug into the Anderson connector.

I used a 100 amp breaker on the truck side, nothing on the trailer side. I started with a solid state relay but I didn't use a big enough heat sink and it overheated and failed in short order. I decided the power savings for solid state wasn't needed access went with a big Sonos like you linked. This one has power to spare and wasn't too bad in price:

PAC PAC-200 200 Amp Relay Battery Isolator, standard https://www.amazon.com/dp/B000CEBXRS...ing=UTF8&psc=1

[Yoda]

I'd think 50' should be enough. I think I started with 40 and was short. It's not too bad to come up a little short because you need a sister l separate piece for the trailer end anyway. I kept the scrap and used it later to make up a set of booster cables that plug into the Anderson connector.

I used a 100 amp breaker on the truck side, nothing on the trailer side. I started with a solid state relay but I didn't use a big enough heat sink and it overheated and failed in short order. I decided the power savings for solid state wasn't needed access went with a big Sonos like you linked. This one has power to spare and wasn't too bad in price:

PAC PAC-200 200 Amp Relay Battery Isolator, standard https://www.amazon.com/dp/B000CEBXRS...ing=UTF8&psc=1

Thanks Neil
Will this relay work
https://www.sonicelectronix.com/item...iABEgL3xfD_BwE

There is a 15% off code listed too.

The reason I asked is a lot of sites show the one you listed as discontinued - makes me wonder, but I am probably over thinking this.
Keith

[Jimmer]

So is 50' of black and 50' of red enough? I don't want to end up short.

Keith

50' was perfect for my travel trailer.