DC-DC Charging Options in Vehicle Mounted Systems

[justinm001]

What engine in the Express? Usually you can add a second alternator easily as these had dual alternator options when ordering a new van. My GMC truck has the Duramax and I purchased the bracket from GM dealer wholesale for 16 bucks (I watched people on Youtube spent several hours building a bracket), the needed bolts cost about $20 because they make you buy a 5 pack, added another idler pulley and installed the serpentine belt for a dual alternator equipped Duramax. As the Express is commonly used for ambulances and other cutaway chassis, it should have had a dual alternator option.

That's exactly what I was thinking. $50 in parts and he can add a 2nd alternator which is like $200 plus the $500 for the wakespeed and he can get like 100amps for under $1000. This is provided he can find a 24v alternator that fits stock brackets and wiring isn't far. No conversion losses or heat issues and the wakespeed will ramp down if alt temps get bad. Plus worst case he burns out the house alt and it doesn't affect chassis.

 

[asot550]

What engine in the Express? Usually you can add a second alternator easily as these had dual alternator options when ordering a new van. My GMC truck has the Duramax and I purchased the bracket from GM dealer wholesale for 16 bucks (I watched people on Youtube spent several hours building a bracket), the needed bolts cost about $20 because they make you buy a 5 pack, added another idler pulley and installed the serpentine belt for a dual alternator equipped Duramax. As the Express is commonly used for ambulances and other cutaway chassis, it should have had a dual alternator option.

2020 express 3500 cutaway, with the 6.0L Vortec V8.

 

[justinm001]

Not sure if this will fit as it doesn't say express but it'll give you 250amps and mechman is a great alternator company

250 Amp Black Billet High Output Alternator for GM 2 pin WITH RVC Bypass

mechman, mechman alternators, high output alternator, mechmanalternators, motor swap, universal, custom, car audio, bass, basshead, subwoofer, amps, voltage, alternator, alt,

www.mechman.com

 

[eXodus]

2020 express 3500 cutaway, with the 6.0L Vortec V8.

there is not much space in the Express van engine bay. I owned two of them.

Not sure if this will fit as it doesn't say express but it'll give you 250amps and mechman is a great alternator company

250 Amp Black Billet High Output Alternator for GM 2 pin WITH RVC Bypass

mechman, mechman alternators, high output alternator, mechmanalternators, motor swap, universal, custom, car audio, bass, basshead, subwoofer, amps, voltage, alternator, alt,

www.mechman.com

That is probably the way to go in the Express GMC Vans. Just switch it out - add another cable to the alternator and an additional ground-strap.

I'm currently running a Victron 10A 24V Tri-Smart in my Chevy RV. It pulls up to 25A on the 12V side.
The Tri-Smart putting out 10A - at Charge voltage - so that's 10A at 28.8V - meaning it needs 290W+ from the 12V system.

They make a 12/24 70a one too. The not smart ones just pump a flat voltage (there's an adjustment screw) the smart has charging profiles iirc. I don't think you can limit the amperage though.

70A @ 28.8V = 2016W / 12V = 168A on the 12V system - that's some major current and draw on the engine.

How is your driving / staying behavior? Do you really need to charge that fast? Most of my charging is solar and I just top of on trips from the alternator.

 

[Supervstech]

there is not much space in the Express van engine bay. I owned two of them.


That is probably the way to go in the Express GMC Vans. Just switch it out - add another cable to the alternator and an additional ground-strap.

I'm currently running a Victron 10A 24V Tri-Smart in my Chevy RV. It pulls up to 25A on the 12V side.
The Tri-Smart putting out 10A - at Charge voltage - so that's 10A at 28.8V - meaning it needs 290W+ from the 12V system.


70A @ 28.8V = 2016W / 12V = 168A on the 12V system - that's some major current and draw on the engine.

How is your driving / staying behavior? Do you really need to charge that fast? Most of my charging is solar and I just top of on trips from the alternator.

02 and up express vans have a lot more room under the hood.

 

[justinm001]

there is not much space in the Express van engine bay. I owned two of them.


That is probably the way to go in the Express GMC Vans. Just switch it out - add another cable to the alternator and an additional ground-strap.

I'm currently running a Victron 10A 24V Tri-Smart in my Chevy RV. It pulls up to 25A on the 12V side.
The Tri-Smart putting out 10A - at Charge voltage - so that's 10A at 28.8V - meaning it needs 290W+ from the 12V system.


70A @ 28.8V = 2016W / 12V = 168A on the 12V system - that's some major current and draw on the engine.

How is your driving / staying behavior? Do you really need to charge that fast? Most of my charging is solar and I just top of on trips from the alternator.

The 70a apparently is 24 to 12v I think the highest 12 to 24 is 30a. If you have a 30a charger and 400ah batteries it'll take over 12 hours to charge and under 10% an hour. Just kinda depends on how you use it.

 

[Zwy]

2020 express 3500 cutaway, with the 6.0L Vortec V8.

Looks easy enough to add a second. https://www.ebay.com/itm/314369126297

I do believe that would fit your 2020, but you would have to check.

 

[eXodus]

Looks easy enough to add a second. https://www.ebay.com/itm/314369126297

I do believe that would fit your 2020, but you would have to check.

there is not a lot of space to the steering column and Cab-Firewall in the Vans - the picture on ebay was clearly from the same engine - but in a Pickup truck.

 

[eXodus]

The 70a apparently is 24 to 12v I think the highest 12 to 24 is 30a. If you have a 30a charger and 400ah batteries it'll take over 12 hours to charge and under 10% an hour. Just kinda depends on how you use it.

Battery size is just one variable - it's about how much you use in between driving.

I'm sometimes only running a slight deficit from Solar - 1 kWh a day. To top this of I need 3-4 hours of driving. For me alternator charging is just a backup If it's your primary way of charging - different story. But I would not recommend doing that. Add more panels. Not more alternators.

 

[justinm001]

Battery size is just one variable - it's about how much you use in between driving.

I'm sometimes only running a slight deficit from Solar - 1 kWh a day. To top this of I need 3-4 hours of driving. For me alternator charging is just a backup If it's your primary way of charging - different story. But I would not recommend doing that. Add more panels. Not more alternators.

I learned its very helpful to arrive at a campsite with full batteries. Especially in an RV it's important to have alternator powering loads while driving. This is why I'm planning a 5kw alternator build with converters.

I agree though add more solar first. Optimize the roof for maximum solar as you can make that 30a from the sun and not the alt.

 

[Zwy]

there is not a lot of space to the steering column and Cab-Firewall in the Vans - the picture on ebay was clearly from the same engine - but in a Pickup truck.

This one does fit, it mounts on passenger side. https://www.nationsstarteralternato...cket-for-Chevy-Express-Van-p/vck-3992v-i6.htm

 

[asot550]

I learned its very helpful to arrive at a campsite with full batteries. Especially in an RV it's important to have alternator powering loads while driving. This is why I'm planning a 5kw alternator build with converters.

I agree though add more solar first. Optimize the roof for maximum solar as you can make that 30a from the sun and not the alt.

There's some really interesting arguments made by GaryBIS (https://www.buildagreenrv.com/mpg-penalty-for-roof-racks-on-camper-vans/) on the Ram promaster forums that more solar isn't always the answer from both a cost and environmental impacts standpoint.

Roof racks and solar panels on the roof are both awful from a fuel efficiency perspective. His simplified testing of a "standard" roof rack with lots of open area showed a 12% decrease in fuel efficiency at 65mph compared to a roof with only a maxxair fan on it. For his Promaster, over a 200k mile van life that's an increase in fuel consumption of 1233 gallons of gas. Even a theoretically perfect rack that had zero impact on the drag coefficient should decrease fuel economy by ~5% just due to the increased frontal area of the vehicle.

Very roughly, alternator charging can convert 0.17 gallons of gas to 1200wh of energy. The same 1233 gallons of gas could thus generate ~8,700 kwh of power. Using PVwatts, a flat mounted 500w solar setup in my area (Cleveland, OH) should generate ~590kwh/year of DC power. At those generation rates, even if I was using all that power 100% efficiently (impossible unless you're a full timer) it'd take 14.75 years (13.3k miles driven/year) to beat out the alternator generation route just from just the fuel economy hit.

There's a million different variables that go into the calculations that can tilt things one way or the other. Vehicle location, solar mounting choice, ratio of miles driven to days in one location, vehicle speed, van life expectancy, etc. etc. will all affect the answer.

Really though, I think it just shows that "more solar" shouldn't always be the default option.

 

[justinm001]

There's some really interesting arguments made by GaryBIS (https://www.buildagreenrv.com/mpg-penalty-for-roof-racks-on-camper-vans/) on the Ram promaster forums that more solar isn't always the answer from both a cost and environmental impacts standpoint.

Roof racks and solar panels on the roof are both awful from a fuel efficiency perspective. His simplified testing of a "standard" roof rack with lots of open area showed a 12% decrease in fuel efficiency at 65mph compared to a roof with only a maxxair fan on it. For his Promaster, over a 200k mile van life that's an increase in fuel consumption of 1233 gallons of gas. Even a theoretically perfect rack that had zero impact on the drag coefficient should decrease fuel economy by ~5% just due to the increased frontal area of the vehicle.

Very roughly, alternator charging can convert 0.17 gallons of gas to 1200wh of energy. The same 1233 gallons of gas could thus generate ~8,700 kwh of power. Using PVwatts, a flat mounted 500w solar setup in my area (Cleveland, OH) should generate ~590kwh/year of DC power. At those generation rates, even if I was using all that power 100% efficiently (impossible unless you're a full timer) it'd take 14.75 years (13.3k miles driven/year) to beat out the alternator generation route just from just the fuel economy hit.

There's a million different variables that go into the calculations that can tilt things one way or the other. Vehicle location, solar mounting choice, ratio of miles driven to days in one location, vehicle speed, van life expectancy, etc. etc. will all affect the answer.

Really though, I think it just shows that "more solar" shouldn't always be the default option.

Interesting test but his mpg varied wildly between each run. Ford states their roof height models don't affect mpg and are identically rated by epa. I'm sure there's some penalty especially at highway speeds. I think if he did much more testing and optimized his design it would under 5%, Maybe under 3%. This is much less of an issue with other vans/trucks where they aren't designed to maximize mpg over all else.

But it's not an apples to apples comparison. Solar works every single day and although shade and weather affects it its still working. Alternators only work when you're driving it. If you're driving more than parked and also using more power while driving vs parked then sure. Even if you're driving a ton you can use suitcase panels or have panels that pop out to help minimize drag.

Someone should make a mono panel system using tiles like 12"x12" then have it fold or roll up.

 

[asot550]

Interesting test but his mpg varied wildly between each run. Ford states their roof height models don't affect mpg and are identically rated by epa. I'm sure there's some penalty especially at highway speeds. I think if he did much more testing and optimized his design it would under 5%, Maybe under 3%. This is much less of an issue with other vans/trucks where they aren't designed to maximize mpg over all else.

But it's not an apples to apples comparison. Solar works every single day and although shade and weather affects it its still working. Alternators only work when you're driving it. If you're driving more than parked and also using more power while driving vs parked then sure. Even if you're driving a ton you can use suitcase panels or have panels that pop out to help minimize drag.

Someone should make a mono panel system using tiles like 12"x12" then have it fold or roll up.

I'm seeing a max difference of 7.7% run to run, but his four runs per "design" should hopefully mitigate some of the randomness. You're right though, it's not a perfect test which would be nearly impossible to conduct.

Do you have a source on that ford transit epa data? As a commercial vehicle, Transit's don't have to undergo mandatory epa testing, so Ford can claim anything they want with an asterisk saying *estimated.

Just from the drag equation, D = Cd * A * .5 * r * V^2 we can see that frontal area (which is effected by roof height) will increase the drag force and affect your mpg. 130 low has a frontal area of 46.41sf, 130 medium=55.95sf, 148 high-EL=62.33sf. Drag force from the air is thus 34% higher for the high roof compared to short low just from the frontal area change. That isn't the only drag the vehicle has to overcome, so the mpg won't be 34% worse, but it definitely effects mpg.

Re: driving vs. solar. What I'm saying is that alternator charging, even by just idling the vehicle (like a generator), can be better than attaching solar panels to the roof with an inefficient roof rack design. Gary's same testing showed a very small mpg (0.1mpg) hit with his existing 315w panel. Using those numbers, it's only an extra 45 gallons of gas over the van's 200k mi life, which could only generate ~317kwh of energy through the alternator. The 315w panel should easily produce more usable power over its life than the vehicle fuel efficiency hit. What it all boils down to is that the details matter.

You're right that suitcase or deployable panels are the best from an MPG standpoint. They also have the benefit of being deployed in optimal locations to minimize shading. The drawback is that you can't generate power with them while driving, or on trips out and about around town. Just like every other choice in the van it's a decision of compromise and requirements. No single solution is going to be the optimal solution for everyone.

I've seen a couple interesting folding panel designs out there, this is the most interesting: https://www.kickstarter.com/project...st-powerful-foldable-and-portable-solar-panel

One other solution I've seen that's very interesting (though not very efficient compared to standard panel) is this in development modular square panel design: https://www.squaresolarinc.com/product/ Using these you could make a panel custom sized to fit any roof shape.

 

[eXodus]

There's some really interesting arguments made by GaryBIS (https://www.buildagreenrv.com/mpg-penalty-for-roof-racks-on-camper-vans/) on the Ram promaster forums that more solar isn't always the answer from both a cost and environmental impacts standpoint.

Roof racks and solar panels on the roof are both awful from a fuel efficiency perspective. His simplified testing of a "standard" roof rack with lots of open area showed a 12% decrease in fuel efficiency at 65mph compared to a roof with only a maxxair fan on it. For his Promaster, over a 200k mile van life that's an increase in fuel consumption of 1233 gallons of gas. Even a theoretically perfect rack that had zero impact on the drag coefficient should decrease fuel economy by ~5% just due to the increased frontal area of the vehicle.

Very roughly, alternator charging can convert 0.17 gallons of gas to 1200wh of energy. The same 1233 gallons of gas could thus generate ~8,700 kwh of power. Using PVwatts, a flat mounted 500w solar setup in my area (Cleveland, OH) should generate ~590kwh/year of DC power. At those generation rates, even if I was using all that power 100% efficiently (impossible unless you're a full timer) it'd take 14.75 years (13.3k miles driven/year) to beat out the alternator generation route just from just the fuel economy hit.

There's a million different variables that go into the calculations that can tilt things one way or the other. Vehicle location, solar mounting choice, ratio of miles driven to days in one location, vehicle speed, van life expectancy, etc. etc. will all affect the answer.

Really though, I think it just shows that "more solar" shouldn't always be the default option.

I've added panels to my RV and built a solar "hump" to actually improve aerodynamic. (or at least no make it worse)

Solar "Hump" for aerodynamics for Class A RV

I'm currently fitting large 435W on my RV. (82x 40 inches) My idea is to fit the long edge (82 inches) across the roof and create a kind of spoiler hump in the front of the RV. (Primary use - is to clear above the vent) This is recently done in Bus design and I saw it on some newer Class C...

diysolarforum.com

over the two years driving around with the panels on the roof I managed to have the same fuel economy or slightly better as before adding two x 435w panels. We did some computer flow simulation and determined the angles of the panels to get some good characteristics.

Page 8 are the final pictures - all the math and flow simulation - are in the pages before.
The leading panel is higher at the back and not flat - the second panel then is taller at the front -and the low at the back - that gives the air ability flow better on top of the RV instead of creating a vortex.

 

[justinm001]

I'm seeing a max difference of 7.7% run to run, but his four runs per "design" should hopefully mitigate some of the randomness. You're right though, it's not a perfect test which would be nearly impossible to conduct.

Do you have a source on that ford transit epa data? As a commercial vehicle, Transit's don't have to undergo mandatory epa testing, so Ford can claim anything they want with an asterisk saying *estimated.

Just from the drag equation, D = Cd * A * .5 * r * V^2 we can see that frontal area (which is effected by roof height) will increase the drag force and affect your mpg. 130 low has a frontal area of 46.41sf, 130 medium=55.95sf, 148 high-EL=62.33sf. Drag force from the air is thus 34% higher for the high roof compared to short low just from the frontal area change. That isn't the only drag the vehicle has to overcome, so the mpg won't be 34% worse, but it definitely effects mpg.

Re: driving vs. solar. What I'm saying is that alternator charging, even by just idling the vehicle (like a generator), can be better than attaching solar panels to the roof with an inefficient roof rack design. Gary's same testing showed a very small mpg (0.1mpg) hit with his existing 315w panel. Using those numbers, it's only an extra 45 gallons of gas over the van's 200k mi life, which could only generate ~317kwh of energy through the alternator. The 315w panel should easily produce more usable power over its life than the vehicle fuel efficiency hit. What it all boils down to is that the details matter.

You're right that suitcase or deployable panels are the best from an MPG standpoint. They also have the benefit of being deployed in optimal locations to minimize shading. The drawback is that you can't generate power with them while driving, or on trips out and about around town. Just like every other choice in the van it's a decision of compromise and requirements. No single solution is going to be the optimal solution for everyone.

I've seen a couple interesting folding panel designs out there, this is the most interesting: https://www.kickstarter.com/project...st-powerful-foldable-and-portable-solar-panel

One other solution I've seen that's very interesting (though not very efficient compared to standard panel) is this in development modular square panel design: https://www.squaresolarinc.com/product/ Using these you could make a panel custom sized to fit any roof shape.

Its not hard to conduct a test but he did a short distance and only 2 trips per. Also used his dash gauge instead of logging the injectors directly. I'm also assuming his van is turbocharged which makes a huge difference when accelerating in traffic. Simply put, he could have used a 5 mile stretch of flat highway at 3am ran 5 tests each way and used the logger data once he hit x mph.

Thats not how drag works when increasing only part of an area. Air doesn't pass through every part of the vehicle equally, thats why we don't drive square cars, slopes and angles can divert the wind. On top of this roofs of cars and especially vans have a negative pressure. I get basically zero airflow on my RV's roof because all the wind is diverted up and over. I know this because my solar panels are tilted and I've left tools up on the roof and they stay.

I don't see a .1mpg hit for panels, mono panels are like 3 inches tall and you can negate that easily. Could even get the sticky ones that are 1/4in if height is a concern. I just don't see a single use case where solar will be negative

 

[eXodus]

This one does fit, it mounts on passenger side. https://www.nationsstarteralternato...cket-for-Chevy-Express-Van-p/vck-3992v-i6.htm

that makes more sense. Would still like to see pictures.

 

[asot550]

Its not hard to conduct a test but he did a short distance and only 2 trips per. Also used his dash gauge instead of logging the injectors directly. I'm also assuming his van is turbocharged which makes a huge difference when accelerating in traffic. Simply put, he could have used a 5 mile stretch of flat highway at 3am ran 5 tests each way and used the logger data once he hit x mph.

Thats not how drag works when increasing only part of an area. Air doesn't pass through every part of the vehicle equally, thats why we don't drive square cars, slopes and angles can divert the wind. On top of this roofs of cars and especially vans have a negative pressure. I get basically zero airflow on my RV's roof because all the wind is diverted up and over. I know this because my solar panels are tilted and I've left tools up on the roof and they stay.

If you read through the procedure Gary addresses some of your concerns. The trip meter and mpg were reset only once 65mph was hit, so acceleration shouldn't be a factor. I agree that logging the injectors would be more accurate than the dash, but a previous test he ran with vortex generators (https://www.buildagreenrv.com/vorblade-vortex-generator-mpg-test/) showed that the on board trip meter for his promaster is at least consistent across runs. The consistency is more important than the accuracy when comparing A/B.

Frontal area definitely works that way with regards to drag. The issue is that changing the shape also effects the drag coefficient since the angles and slopes are also changing. Drag coefficient is extremely difficult to measure without a wind tunnel though, so the only way to get a good sense of A/B differences is to run testing like Gary did.

Re: your tool anecdote, looking at your rig I wouldn't expect your tools to move because of how your solar rack is designed. Air can't flow through the panels, so as you're driving the airstream is being diverted up to the top of the panels and flowing across that flat surface. You'd run into issue if the panels weren't the entire length of the vehicle, the air would detach and create a lot of turbulence at the panel edges. How your rig is designed would be what I would consider to be a good solar installation.

A "bad" solar install would use a rack like this: https://flatlinevanco.com/collections/promaster/products/promaster-136-low-pro-roof-rack but then leave lots of open air within the rack which is a relatively common installation method out there. That would have a significantly higher drag coefficient penalty, and is much more similar to Gary's unoptimized rack.

 

[asot550]

I've added panels to my RV and built a solar "hump" to actually improve aerodynamic. (or at least no make it worse)

Solar "Hump" for aerodynamics for Class A RV

I'm currently fitting large 435W on my RV. (82x 40 inches) My idea is to fit the long edge (82 inches) across the roof and create a kind of spoiler hump in the front of the RV. (Primary use - is to clear above the vent) This is recently done in Bus design and I saw it on some newer Class C...

diysolarforum.com

over the two years driving around with the panels on the roof I managed to have the same fuel economy or slightly better as before adding two x 435w panels. We did some computer flow simulation and determined the angles of the panels to get some good characteristics.

Page 8 are the final pictures - all the math and flow simulation - are in the pages before.
The leading panel is higher at the back and not flat - the second panel then is taller at the front -and the low at the back - that gives the air ability flow better on top of the RV instead of creating a vortex.

Love the design! I can tell some thought went into it.

 

[Zwy]

that makes more sense. Would still like to see pictures.

I was looking thru some RV forums and it was the kit they used for adding a second alternator. I'd like photos too but can't seem to find any. It was still tight by the description.