Anyone else running a Renogy 40A DC-DC charger alongside solar — or is it overkill?

Just finished rewiring my Transit van conversion and I've gone with a Renogy 40A DC-DC (DCC50S) alongside a 200W roof panel feeding into a 200Ah lithium (a Fogstar Drift, if anyone's curious). The idea being the DC-DC tops up properly from the alternator on driving days, and the solar handles the stationary stuff. Total cost for the charging setup came to around £380 all in, which felt steep but I wanted it done properly.

Thing is, I'm now second-guessing whether the 40A DC-DC is doing anything the 20A version couldn't. On a typical two-hour motorway run I'm pulling maybe 60-70Ah back in, which is decent, but I'm not sure I'd notice the difference on a shorter hop. The van's a 2019 Transit with the 130ps engine, and from what I've read the alternator should handle the load fine, but I haven't actually checked charge current at the battery terminals with a proper meter yet — it's on the to-do list.

Has anyone done a direct comparison between the 20A and 40A versions, or got real-world numbers from a similar setup? Also wondering if there's a risk of the alternator getting too warm on a hot day stuck in traffic — some people seem convinced it's an issue, others say it's fine on modern Fords. Would love to hear from anyone who's been running a similar rig for a full season or two.

Brummie88 | 847 posts | West Midlands

@ShedGenius79 Nice setup mate! I've got a similar arrangement in my Ducato — 30A DC-DC alongside 300W solar into a 100Ah lithium. Honestly the DC-DC is worth every penny in my opinion, especially with modern smart alternators on Transits that would throttle charging without it. The DCC50S is a solid bit of kit too.

One thing I'd suggest — keep an eye on your combined input sources if both are hammering the battery simultaneously on a good sunny day whilst driving. Shouldn't cause issues with a Fogstar Drift since the BMS handles it well, but worth monitoring temps initially just to be sure.

Overkill? Definitely not. If anything I'd say it's the sensible approach for year-round touring. What capacity DC-DC were you running before, or is this a fresh build throughout?

BitsAndBobs9 | 234 posts | Yorkshire

@ShedGenius79 Cracking choice with the Fogstar Drift — solid battery for the money. I've been running a similar dual-input setup in my Sprinter for about 18 months now and honestly the DC-DC alongside solar is anything but overkill. The two sources complement each other really nicely; cloudy day in a Tesco car park? The alternator's got your back. Blazing sunshine on a wild camp? The panel takes the strain and saves your alternator the hassle. One thing worth checking — make sure your DCC50S firmware is up to date, Renogy pushed an update a while back that improved the lithium charge profiles noticeably. Also worth logging your actual charge cycles over a few weeks before drawing conclusions about whether 40A is "too much." You might surprise yourself on those short driving days.

SaltyMaker | 612 posts | Array

Running almost the same combo at my static but with a 60A DC-DC instead — honestly the 40A is fine for a single 200Ah, no need to upsize unless you're adding more batteries later.

One thing worth knowing: the DCC50S has built-in MPPT so your 200W panel feeds through it directly, no separate controller needed. Keeps the wiring tidy.

The DC-DC really shines on overcast days when solar's barely doing anything but you're driving — Fogstar Drift will be nicely topped up after an hour on the motorway.

Only watch-out I'd flag — make sure your alternator is smart/EFB-aware. Some newer Transits do funny things with voltage regulation and it can confuse DC-DC chargers occasionally. Worth double-checking in the Renogy app if you've got intermittent charging issues.

LeeParker | 1,203 posts | Derbyshire

@ShedGenius79 Not overkill at all — the DC-DC and solar complement each other nicely rather than competing. The real win is on overcast days when your panel's barely producing; the DC-DC keeps the Drift topped up properly from the alternator without you even thinking about it. One thing worth checking: make sure your DCC50S firmware is up to date — Renogy pushed an update a while back that improved the lithium charging profiles noticeably. Also worth enabling the solar input on the unit if you haven't already, as it'll intelligently manage both sources simultaneously. With 200Ah you'll find 40A is a very sensible match — fast enough to matter, without hammering your alternator on shorter runs.

CraftyRanger | 487 posts | Cambridgeshire

@ShedGenius79 Nice setup! One thing worth mentioning that nobody's touched on — with the DCC50S specifically, make sure your alternator is up to the job before letting it rip at full 40A draw continuously. Some of the newer Ford Transit alternators with smart charging (variable voltage) can play funny buggers if you haven't configured the DC-DC input settings correctly. Worth checking the Renogy app and tweaking the charge profile to suit your Fogstar's BMS requirements too — Fogstar publish recommended settings on their site. Also keep an eye on ambient temps in that van; these units do throttle back when it gets warm in the back. Beyond that though, 200W solar plus a DC-DC is genuinely a brilliant pairing for a Transit build. You'll barely notice you're off-grid on a typical trip.

VoltGeek | 2,847 posts | West Yorkshire

@ShedGenius79 Solid choice on the Fogstar Drift — cracking battery for the money. One thing I'd flag specifically with the DCC50S: make sure your alternator is reasonably modern before leaning on it hard. Older Transits (pre-Euro 6 roughly) with traditional alternators can struggle a bit under sustained 40A draw, especially at idle in traffic. Worth keeping an eye on your chassis battery voltage while driving initially. The solar doing the heavy lifting when you're parked means the DC-DC is more of a top-up on the move anyway, so you've balanced it nicely. What size cable did you run between batteries?

OBT_Solar | 834 posts | West Yorkshire

@ShedGenius79 Solid choices all round. One thing I'd add that hasn't been mentioned yet — keep an eye on your alternator health if you're doing lots of short runs. The DCC50S will happily pull a consistent 40A, and on a modern Transit with a smart alternator that's already working hard, it can add up over time. Worth fitting a temperature sensor on the alternator if you haven't already, or at least checking it runs cool after a typical journey. The Fogstar Drift will take everything you throw at it no bother, so the weak point in that chain is almost certainly going to be the vehicle side rather than the leisure setup. Otherwise genuinely cracking combination for a van build — 200W solar will keep you ticking over nicely on site when the engine's off.

BoatOllie | 1,203 posts | Norfolk Broads

@ShedGenius79 Great combo — I ran almost identical kit on my narrowboat before switching to a van. One thing worth flagging: the DCC50S has a built-in alternator protection feature that throttles output if it detects voltage drop, which is brilliant for older or smaller alternators. Worth checking what alternator your Transit has — some of the newer Euro 6 engines run smart alternators with variable voltage, and the DC-DC will handle that just fine, but it's good to confirm rather than assume. Enjoy the Fogstar, mine's been bulletproof. 🙂