DCDC and MPPT for Van Life?

[gianaleo]

Hi! I'm finalizing my van life setup and was hoping someone could give some advice. Here's what I'm thinking:

4 x 12v 100ah lithium batteries, Renogy (already purchased)
3000w 12v purse sine inverter/charger, Renogy (went a bit larger for potential future expansion purposes)

What I am struggling on, is my b2b set up and solar/MPPT charger set up.

I originally purchased Renogy's DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT because I liked the fact that it was a DC/DC and MPPT all in one - being a newbie it was less intimidating, however, the more I read up on it, the more I am thinking this will not really work too well. Reason being, is that while it is advertised as 50a, it is in fact 25a and 25a when you are using it for both a b2b and a MPPT.

If I used this with 100w 12v panels, let's say 2 or 3 of Renogy's, wired in series, it would be:
24v/16.7a or 36v/16.7a respectively
To my understanding, because Renogy's 50a charger is 12v, this would not work. I would have to wire in parallel (which is of course more wiring etc to understand for a noob), but even if I did, it would be:
12v/33.4a or 12v/50.1a

Because the MPPT caps out at 25a when also using the b2b, I would essentially be limited/missing out, no? For this reason, I am thinking it would make more sense to return this and go with Victron, either their 100v/30a or 100v/50a. This way I also have the ability to expand in the future if I choose.

Does this all make sense, am I doing this correctly or is my math wrong somewhere? And if I go this Victron route, does anyone recommend a specific dcdc charger for a 2018 Ram Promaster 2500 with 400ah lithium? Any input someone more experienced can give would be greatly appreciated!

Note: We will be running quite a bit and working from the van full-time, hence our system is on the larger size for a van.

 

[Dzl]

Hi! I'm finalizing my van life setup and was hoping someone could give some advice. Here's what I'm thinking:

4 x 12v 100ah lithium batteries, Renogy (already purchased)
3000w 12v purse sine inverter/charger, Renogy (went a bit larger for potential future expansion purposes)

What I am struggling on, is my b2b set up and solar/MPPT charger set up.

I originally purchased Renogy's DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT because I liked the fact that it was a DC/DC and MPPT all in one - being a newbie it was less intimidating, however, the more I read up on it, the more I am thinking this will not really work too well. Reason being, is that while it is advertised as 50a, it is in fact 25a and 25a when you are using it for both a b2b and a MPPT.

While I don't have experience with this specific product, I believe your understanding is correct so far.

If I used this with 100w 12v panels, let's say 2 or 3 of Renogy's, wired in series, it would be:
24v/16.7a or 36v/16.7a respectively
To my understanding, because Renogy's 50a charger is 12v, this would not work. I would have to wire in parallel (which is of course more wiring etc to understand for a noob), but even if I did, it would be:
12v/33.4a or 12v/50.1a

So I don't know specific specs for the panels you are using, but a typical 100W "12v" panel produces roughly 5.5ish Amps @ 18ish Volts. So your numbers are a bit off. It looks like you assumed 12V for a "12V" panel which is a logical assumption, but wrong.

3 typical 100W panels in parallel would likely be a bit under 17A @ 18V or so.
3 typical 100W panels in series would likely be about 5.5A @ a bit under 60V

Input amps are not the real limitation with the DCC50S, input voltage is (<25V), and output amps (this is what the 25A / 25A max is, output amps).

The issue with the 25V limitation is it forces you to wire in parallel, and even then can be an issue at low temperature. To figure out if a panel will work, you need to look at the datasheet or sticker on the back, there is a figure called 'open circuit voltage (VOC)' take that value and multiply by 1.25x if you want to be conservative, or 1.20x if you are sure the panels will never charge when its below 0 Fahrenheit, whatever that number is must be below 25V to be compatible with the DCC50S. There are more precise ways to do the math, but this will give a safe ballpark.

The 25A limitation is its on the output side. The max either portion can produce is 25A x battery voltage (~12V) or roughly 300W. With your setup this would not be a limitation on the solar side since you will only have 300W of solar.

So I think the DCC50S would work for your situation. But there are advantages to going with a separate charge controller and B2B charger. Expandability being one advantage, higher input voltage being another. And of course Victron make higher quality components compared to renogy so there's that.

 

[jaydub]

I have the DCC50S working in my van set up I just finished. I have a portable solar suitcase 200W that I have been testing with then and plan to add a fixed 200 W panel later. I am driving further with the system and the DCC50S is doing a great job charging. Using the Renogy BT2 I see the alternator charging 40+ amps by itself (it isn’t a smart alt). So if you are driving I would switch off the solar and let the alternator have it’s way so you are getting the most from your unit. When off the grid for a while I plan on having combined 400W of solar panels which will be just under 25V limit on the DCC50S. I only have one 170ah battery mainly to run a dometic 12V fridge and a few lights and chargers. For me, this works great.

 

[mikefitz]

Renogy's DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT

The max either portion can produce is 25A

Some of the above comments regarding the DCC50S are incorrect. On engine charging only it will deliver up to 50 A into the battery, with no engine charging and solar input it will support up to 600 watts of solar with the panels ('12v' panels in parallel) and generate up to 50 A. If there is both solar and engine input then the limit is 25A each.
Four 100 watt panels in parallel would produce about 30A in ideal conditions with no engine input.

In practice the 25A limit whilst driving and having solar input would work quite well and limit the power taken from the alternator to save limits and the combined total in daytime will not be too far from the 50A. Of course when the engine is not running you will get up to the 30A from solar or more with extra panels.

Since you already have the unit i would install and see how things turn out, you could add a Victron controller at a later date and use the Renogy just for engine charging at 50 A.

The alternative from Victron, a 100/30 and a DC to DC Orion 30A will not significantly improve things, and cost at least twice the cost of the Renogy unit. However Victron units are easily programmable via the app, supply performance info and are well designed , reliable units. Using a controller with a higher input voltage would allow you to use the cost effective larger panels, subject to roof space.

Unless you use all the roof space on a promaster 400 watts or so is about the limit.

If you are full time in the van and have no or infrequent shore charging, then unless you are in part of the world with reliable solar all year round, then engine charging may be important.
I suggest estimating your power consumption and plan the solar/engine power requirements from that.

Although some use a direct charge method on your and similar vehicles, most manufactures suggest around 50 A as a realistic additional draw on the van electrical system for reliability and thus a DC to DC charger is required

Mike

 

[Aledi]

I have the DCC50S working in my van set up I just finished. I have a portable solar suitcase 200W that I have been testing with then and plan to add a fixed 200 W panel later. I am driving further with the system and the DCC50S is doing a great job charging. Using the Renogy BT2 I see the alternator charging 40+ amps by itself (it isn’t a smart alt). So if you are driving I would switch off the solar and let the alternator have it’s way so you are getting the most from your unit. When off the grid for a while I plan on having combined 400W of solar panels which will be just under 25V limit on the DCC50S. I only have one 170ah battery mainly to run a dometic 12V fridge and a few lights and chargers. For me, this works great.

I am planning to follow a similar configuration with the DCC50S.
May I ask you which sizes of cables have you used to connect the engine/alternator battery to the DCC50S ?

Following this schematics:

RV Solar Power Blue Prints

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

4 gauge are suggested, but the DCC50S have a limit of 660w at 12 volt (55amp).
Isn't the 4 gauge wire too big?

 

[jaydub]

I am planning to follow a similar configuration with the DCC50S.
May I ask you which sizes of cables have you used to connect the engine/alternator battery to the DCC50S ?

Following this schematics:

RV Solar Power Blue Prints

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

4 gauge are suggested, but the DCC50S have a limit of 660w at 12 volt (55amp).
Isn't the 4 gauge wire too big?

4 gauge running back to the rear of my van, about 12 ft. It was a service van that already had the wiring and 80a breaker to the rear to power a 2 ton lift crane mounted on the bumper. Great find.

 

[Aledi]

4 gauge running back to the rear of my van, about 12 ft. It was a service van that already had the wiring and 80a breaker to the rear to power a 2 ton lift crane mounted on the bumper. Great find.

thanks.

lucky you had some wiring ready to be used, mine was an ex electric company workshop, but they stripped all the good gears before the sale

 

[rickst29]

With your huge Solar configuration, the "little" Renogy is not the way to go (requiring several SCCs). My scheme will still involve two Solar controllers for you, because the little one (shared with the engine boost/regulator device) must be limited to 30A, and not more than about 500W of panels.

Under the hood, instead of the Renogy DC-->DC, you install "12V" --> 36.0V boost regulator, rated for up to 15A. They cost about $50. Then into the special "little" MPPT SCC, you have a 24-VDC Coil "tester" relay and a regular automotive 5-pin Reley (12v Coil, at least 30/40 switched Amps the power pins). Another Relay under the hood is used to only engage the Boost Converter when the engine is running (I actually have both a Relay and a dashboard switch to "enable", but I've got a travel trailer, rather than a Van - and my Bargman 7-pin connector must also be capable of towing other Trailers at only 12V).

Up on the roof, you divide your array (maybe 600-700 rated watts into a "40A" MPPT, with only 500 rated watts into the switched "30A" MPPT.) The "PV +" from the roof goes into the "normally closed" leg of another 5-pin automotive Relay. (in my own Trailer, MPPT Voltage from the "Real Array" is about 65V, and a regular automotive Relay does fine - even though they are traditionally rated for only 32V switched voltage.) But coming from the engine compartment, your new "fake solar array" cable always carries either 36.0 Volts (engine is running), or nothing. The 24v detector Relay switches 12v power (from the batteries) "on" when more than 24V is present. Mine (and those which other have installed using my scheme) are also prefectly fine with handling 36v on the coil connection all day. But it lets go when that voltage falls to less than about 18V (both 14.6V and 12.8V are far less than that figure).

When that coil gets pulled in (by 36V present on the "fake solar" cable), it sends 12v power through its power pins and switches the 5-pin automative Relay: The real panel array get disconnected, and the 36 Volt "fake panel" is connected into the MPPT instead. The MPPT should go hunting and find the new 36.0V optimal power point almost immediately, and begin charging your battery string - or not, as determined my your MMPT charging parameters.

Although I have about 500W of "rated" Solar on the roof of my travel trailer, I always end up flicking the "magic voltage" switch on the 4Runner dash when I tow my own Trailer - because 500 "rated watts" is beaten by 435 watts all the time (under clouds, and even at night), except for about 1/2 hour around Solar noon on a perfect day.

If you treat the MPPT controller as a "sunk and necessary cost", this adds only about $80 of new parts. It works GREAT!

 

[rickst29]

Hi! I'm finalizing my van life setup and was hoping someone could give some advice. Here's what I'm thinking:

4 x 12v 100ah lithium batteries, Renogy (already purchased)
3000w 12v purse sine inverter/charger, Renogy (went a bit larger for potential future expansion purposes)

What I am struggling on, is my b2b set up and solar/MPPT charger set up.

I originally purchased Renogy's DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT because I liked the fact that it was a DC/DC and MPPT all in one - being a newbie it was less intimidating, however, the more I read up on it, the more I am thinking this will not really work too well. Reason being, is that while it is advertised as 50a, it is in fact 25a and 25a when you are using it for both a b2b and a MPPT.

If I used this with 100w 12v panels, let's say 2 or 3 of Renogy's, wired in series, it would be:
24v/16.7a or 36v/16.7a respectively
To my understanding, because Renogy's 50a charger is 12v, this would not work. I would have to wire in parallel (which is of course more wiring etc to understand for a noob), but even if I did, it would be:
12v/33.4a or 12v/50.1a
...

Yep, it's a really bad choice for this, because the "alternator" and "PV" input ports are separate - and limited to only 25A each. I(sc) on your panels is 5.86A each, so only 4 panels could be put on each Renogy - you'd need 3 of them, at almost $900 total cost.