DC-DC charger wiring

[AH64ID]

Incase 440A was not enough lol

Yeah, exactly what I was thinking. Seems more like marketing than a realistic need.

 

[jsalbre]

Yeah, exactly what I was thinking. Seems more like marketing than a realistic need.

I mean, they offer a pair of 220s on the Cummins when the Hemi got a 220 and a 160 as the high option. They apparently thought someone needed more. Probably ambulance builders.

 

[AH64ID]

I mean, they offer a pair of 220s on the Cummins when the Hemi got a 220 and a 160 as the high option. They apparently thought someone needed more. Probably ambulance builders.

I always figured the second alternator on the Hemi being a 160 was a limitation of either the engine or space. The ‘25 Hemi duals output 400A.

Even with 440A the HAPP is only 300A. I wonder if that’s higher on the ‘25’s.

 

[RAM_GA]

RAM_GA Unless I'm way off on my electric needs under normal I expect to be well equipped to handle the extra amps. M reasoning is that my HO Cummins came with just one alternator, with the option of a 2nd one when ordered. I wanted to make sure I had enough for whatever I threw at it in the future. I wish I would have ordered the aux switches, but I didn't know better at the time. Live and learn.

Thanks,
Larry

With 2 alternators you are in good shape

 

[jsalbre]

I always figured the second alternator on the Hemi being a 160 was a limitation of either the engine or space. The ‘25 Hemi duals output 400A.

Even with 440A the HAPP is only 300A. I wonder if that’s higher on the ‘25’s.

Yeah, I always figured it was some kind of packaging issue, but there seems to be space when I look. Maybe it’s some interference issue and the new alternators are a different shape, or maybe it’s just so they can say “look, you need the diesel for ‘real’ heavy duty use!”

 

[HarryN]

There are a couple of ways to move power back to the trailer.

The conventional way is to use DC - DC converters, but as you see, the wire size can be pretty large, especially for 12 volt.

A high current DC wire or connector breaking while driving is a big arc.

If your wife or kids unplug it while live, that can be pretty exciting as well.

The main challenge is that AC arcs are self extinguishing, but DC arcs are not.

___________-

It isn't as obvious, but a much safer method is to put an inverter near the starter battery and run 120 vac and an RV type outlet at the back of the truck.

Plug the trailer into the truck and use the 120 vac - DC charger that is already in the trailer.

10 awg stranded wire can easily move 2 kW @ 120 vac and you can buy 30 amp RV plugs all over the place.

This approach is very common in the conversion van world. I do it all of the time with my customers.

( I build mobile electrical systems and disaster relief power systems for people )

____________

The purpose of the dual alternators is to improve low rpm capability, which is a common problem.

There are people with Transits that have dual 220 amp alternators, and it is common to be running up against the limits of the systems, especially for air conditioning applications.

 

[ramblinChet]

EDIT - the calculations in this post are incorrect. See @AH64ID reply below for correct calculations. I did not include pulley ratios.

Just to add a bit of additional information to this discussion - temperature and RPM each have an impact on alternator output. For reference, if I am cruising along at 1700 RPM and it's 200° F under the hood, my 380-amp system is only able to deliver 171 amps. You know me, I like to run my mechanical or electrical systems with significant headroom so out of those 171 available amps, I would target using around 50% (86 amps), certainly not more than 75% (128 amps).

Here are the charts for the alternators in my 6.4L HEMI equipped 2021 Tradesman:

Primary:


Secondary:

 

[AH64ID]

Just to add a bit of additional information to this discussion - temperature and RPM each have an impact on alternator output. For reference, if I am cruising along at 1700 RPM and it's 200° F under the hood, my 380-amp system is only able to deliver 171 amps. You know me, I like to run my mechanical or electrical systems with significant headroom so out of those 171 available amps, I would target using around 50% (86 amps), certainly not more than 75% (128 amps).

Here are the charts for the alternators in my 6.4L HEMI equipped 2021 Tradesman:

Primary:
View attachment 80516

Secondary:
View attachment 80517

That’s alternator rpms, not engine rpms.

At 1700 engine rpms the primary is turning 4,930 and the secondary 4,624. That gives you over 297A available, not 171A, at 200°F.

 

[ramblinChet]

That’s alternator rpms, not engine rpms.

At 1700 engine rpms the primary is turning 4,930 and the secondary 4,624. That gives you over 297A available, not 171A, at 200°F.

Thank you for catching that and honestly, I feel much better now!!!

 

[dieselscout80]

That’s alternator rpms, not engine rpms.

At 1700 engine rpms the primary is turning 4,930 and the secondary 4,624. That gives you over 297A available, not 171A, at 200°F.

Thanks, but how did you get that engine rpm #?

 

[H3LZSN1P3R]

That’s alternator rpms, not engine rpms.

At 1700 engine rpms the primary is turning 4,930 and the secondary 4,624. That gives you over 297A available, not 171A, at 200°F.

I was gonna say the same thing lol. Plus I believe the OEM alt is 180A on the 19+ where that chart says 160A

 

[AH64ID]

Thanks, but how did you get that engine rpm #?

The pulley ratios are published on the amperage chart. 1700x2.90=4,930.

 

[AH64ID]

I was gonna say the same thing lol. Plus I believe the OEM alt is 180A on the 19+ where that chart says 160A

The 160A chart is for the 6.4 secondary alternator.

 

[dieselscout80]

The pulley ratios are published on the amperage chart. 1700x2.90=4,930.

Thanks it makes sense now. I missed the ratio on the chart.

 

[HarryN]

I am still learning about how the ram setup works, but at least on Transit vans, the way that the dual alternator is implemented is to first apply field current to alternator 1 and none to alternator 2.

The field current on alternator 1 is increased until the alternator cannot keep up, then the controller starts to ramp up the field current on alternator 2.

I have not measured the individual power needs of a ram truck, but on the ram van, it can easily use up 100 amps @12 volt just for common items like lights and fans. I am "speculating" that the radiator fan on a truck uses at least as much as the vans.