Renogy DC DC Charger w/ MPPT

[Mash]

This would be a good time to find the actual specs on the alternator. Rated output might be stamped/labeled on the alt, or you can use a Ford-specific VIN decoder to see what it came with. Once you have the rating check out this excellent video to see how the rating relates to battery charging duties.

Per the VIN it is a 130 amp alternator

 

[Mash]

Watching the alternator video and the fact that it seems I have a 130 A alternator, the 30A version seems to be the best fit. And also I would have to pay to ship the 30A version back to Renogy.....

 

[EnsignR]

Be aware that the 50 amp charger will only pull 25 amps from the alternator if there is any solar production at all.

Could you just add a switch/breaker that disconnects the solar while you're driving?

 

[John Frum]

Could you just add a switch/breaker that disconnects the solar while you're driving?

Yes.

 

[Mash]

Is there a setting in the app for that too?

 

[Spire]

Could you guys help me out with a question about shutoff switches?

So I'm wiring up my 30A DC-DC/MPPT and I have a shutoff switch on the PV (+) cable between the solar panel and the charger.

My house battery bank is wired to a (+) bus bar, and I also have a shutoff switch between these two.
Should I also have a shutoff switch between the starter battery and the DC-DC/MPPT unit?

I'm thinking that if I want to remove all power from the system to work on it, there could still be a possibility of power coming through from the starter battery if I don't have a switch here.

Am I thinking correctly here?

The (+) output on the DC-DC/MPPT unit is also wired to the (+) bus bar, so would it make sense to just have one shutoff switch between the charger and bus bar and get rid of the one between the solar panel and charger? If I had this switch, I could turn it off along with the house battery switch to remove power from everything that runs off the bus bar, but I would still have power to the PV (+) and battery inputs on the charger. This doesn't sound like what I want.

Any thoughts?

 

[John Frum]

Could you guys help me out with a question about shutoff switches?

So I'm wiring up my 30A DC-DC/MPPT and I have a shutoff switch on the PV (+) cable between the solar panel and the charger.

My house battery bank is wired to a (+) bus bar, and I also have a shutoff switch between these two.
Should I also have a shutoff switch between the starter battery and the DC-DC/MPPT unit?

I'm thinking that if I want to remove all power from the system to work on it, there could still be a possibility of power coming through from the starter battery if I don't have a switch here.

Am I thinking correctly here?

The (+) output on the DC-DC/MPPT unit is also wired to the (+) bus bar, so would it make sense to just have one shutoff switch between the charger and bus bar and get rid of the one between the solar panel and charger? If I had this switch, I could turn it off along with the house battery switch to remove power from everything that runs off the bus bar, but I would still have power to the PV (+) and battery inputs on the charger. This doesn't sound like what I want.

Any thoughts?

Would need to see a diagram of your proposed topology to give decent advice.
You should use a double pole disconnect for the pv wires.
Note that the DC-DC/MPPT is a non-isolated charger so the pv positive goes to the charger but the pv negative goes to the system negative busbar either physically or logically.

 

[Spire]

Would need to see a diagram of your proposed topology to give decent advice.
You should use a double pole disconnect for the pv wires.
Note that the DC-DC/MPPT is a non-isolated charger so the pv positive goes to the charger but the pv negative goes to the system negative busbar either physically or logically.

Thanks, here is my diagram.

 

[John Frum]

Since you used 4 awg wire between starter battery and dc2dc charger you can use a 150 amp terminal fuse.
Fuse's protect wires not dc2dc chargers.
Higher ampacity fuses generally have lower resistance.

Same thing for the fuse between the dc2dc charger and the positive busbar.

best practice is a double pole switch on the pv circuit.

Suggest you use a fused positive busbar as it cuts down the number of joints and thereby reduces resistance
It also saves space which is usally at a premium in mobile builds.

Still going with that mini air conditioner?
Since it appears to require 25 amps at 24 volts that will mean more than 50 amps at 12 volts
You need to wire that off the main busbars with 6 awg wire and a 100 amp fuse.
The wire from the buck converter to the air conditioner can be 10 awg with a 30 amp fuse.
Pretty sure I already explained this to you in another thread.
Did you just ignore that suggestion?

 

[Spire]

Since you used 4 awg wire between starter battery and dc2dc charger you can use a 150 amp terminal fuse.
Fuse's protect wires not dc2dc chargers.
Higher ampacity fuses generally have lower resistance.

Same thing for the fuse between the dc2dc charger and the positive busbar.

best practice is a double pole switch on the pv circuit.

Suggest you use a fused positive busbar as it cuts down the number of joints and thereby reduces resistance
It also saves space which is usally at a premium in mobile builds.

Still going with that mini air conditioner?
Since it appears to require 25 amps at 24 volts that will mean more than 50 amps at 12 volts
You need to wire that off the main busbars with 6 awg wire and a 100 amp fuse.
The wire from the buck converter to the air conditioner can be 10 awg with a 30 amp fuse.
Pretty sure I already explained this to you in another thread.
Did you just ignore that suggestion?

Hey, thanks for the advice. I actually followed your suggestion with the mini AC unit and changed my wiring diagram around. I followed up with the manufacturer they told me it needs to be wired with 10 AWG and a 25 amp fuse. Maybe I miscommunicated something with the requirements in my previous posts.

 

[John Frum]

Secondary distribution(fuse blocks) are generally limited to 30 fault amps(24 continuous amps) per circuit.

 

[Cal]

Since you used 4 awg wire between starter battery and dc2dc charger you can use a 150 amp terminal fuse.
Fuse's protect wires not dc2dc chargers.
Higher ampacity fuses generally have lower resistance.

It's true fuses should protect the wire, but why on earth use a 150A fuse? If the dc/dc pulls 75A, wouldn't a 100A fuse (or lower) still protect the wire. There are many instances where there's a "soft short" and the 150A fuse won't open. I like to select my fuses by determining what the max current the cable will carry under normal conditions. The fuse should blow if the current is 20% above max current.

 

[John Frum]

It's true fuses should protect the wire, but why on earth use a 150A fuse?

Glad you asked.
Because generally speaking the higher the fuse rating the lower the resistance.
Since the fuse protects the wire, why turn expensive solar electricity into waste heat unnecessarily?

If the dc/dc pulls 75A, wouldn't a 100A fuse (or lower) still protect the wire.

Yes but, see above.

There are many instances where there's a "soft short" and the 150A fuse won't open.

Please name 3.
If the fuse doesn't blow, I don't really care.
I do understand the battery may be discharge to low voltage disconnect, still don't care.

I like to select my fuses by determining what the max current the cable will carry under normal conditions. The fuse should blow if the current is 20% above max current.

I used to think that to.
Upon a good amount of reflection I now consider that to be the minimum fuse size.
The maximum being the rating of the wire.

 

[John Frum]

Just to be clear, I use the 80% rule for secondary distribution especially if its going inside walls or similar.
For the dc core of the system where the high current wires are in free air I fuse to the max of the conductor.

 

[brb58]

Glad you asked.
Because generally speaking the higher the fuse rating the lower the resistance.

Not even close to being enough to even worry about. I actually use a breaker which does have more resistance than a fuse but even that is not enough to worry about on a circuit driving an MPPT.

BTW, if you had some insulation wear off the wire and it started to hit some metal material attached to ground, you could potentially have a short that didn't quite pull enough current to blow the fuse but plenty to make that area very hot and start a fire.

 

[John Frum]

BTW, if you had some insulation wear off the wire and it started to hit some metal material attached to ground, you could potentially have a short that didn't quite pull enough current to blow the fuse but plenty to make that area very hot and start a fire.

That could happen with a fuse rated for the 80% rule to, just a tiny bit less likely and not enough to worry about.

 

[brb58]

That could happen with a fuse rated for the 80% rule to, just a tiny bit less likely and not enough to worry about.

I have a 30A Victron MPPT. I use a 50A breaker driving a 6AWG wire. Absolutely ZERO need or want to have a 100A fuse protecting the circuit.

 

[bradbill]

I have a 30A Victron MPPT. I use a 50A breaker driving a 6AWG wire. Absolutely ZERO need or want to have a 100A fuse protecting the circuit.

Totally agree. I am the CTO of an engineering company and I would fire the engineer who fused that much higher than the actual fixed load like that.

 

[Cal]

Totally agree. I am the CTO of an engineering company and I would fire the engineer who fused that much higher than the actual fixed load like that.

I doubt an engineer would do that. Usually the wire size is multiple times greater than max current. In this case you always fuse the circuit capability and not the wire.

The fuse resistance is peanuts compared to the dc/dc losses. That’s no argument to choose the largest possible fuse.

 

[bradbill]

I doubt an engineer would do that. Usually the wire size is multiple times greater than max current. In this case you always fuse the circuit capability and not the wire.

The fuse resistance is peanuts compared to the dc/dc losses. That’s no argument to choose the largest possible fuse.

I agree...there is no way any engineer that worked at my company would ever do something like that