Plan every DC decision in minutes — not forums.
EV fast charging, solar panels and batteries all run on direct current. 9DC gives you nine free calculators and plain-English guides to size, price and compare them — then connects you with qualified installers when you are ready.
Watch power taper after 50% and drop hard near 80% — the reason road-trippers unplug early.
Nine calculators. One for every DC question.
Results update as you type and every assumption is visible. Pick a tool:
DC fast-charge time
Minutes from any start to target charge, with a real taper curve.
02Charging cost vs gas
Monthly cost by home/fast-charge mix, savings per year.
03Road-trip stops
How many stops, how long on chargers, total trip time.
04Solar sizer
Array kW, panel count, roof area and cost from your bill.
05Solar payback
Payback years, 25-year gain and lifetime cost per kWh.
06Battery bank
kWh and amp-hours for off-grid, RV, van and backup.
07Runtime
How long a power station runs your fridge, CPAP or laptop.
08Wire gauge
AWG/mm², voltage drop and fuse size for DC runs.
09Ohm's law
Solve volts, amps, ohms, watts and watt-hours.
From estimate to installed — without the sales gauntlet.
Solar arrays, home battery backup, Level 2 home chargers, off-grid kits and commercial DC fast chargers. Describe the project once; we route it to qualified providers who serve your area.
- Your calculator result attaches automatically — no re-explaining
- Free and no obligation; you choose who contacts you
- We never sell your details to data brokers
- Homeowners, landlords, fleets and businesses welcome
Guides that skip the jargon
DC fast charging, explained
Why 350 kW chargers rarely deliver 350 kW, and how to charge faster.
Read → EVNACS, CCS1, CCS2, CHAdeMO
Which plug fits which car, and what adapters really do.
Read → SolarDC- vs AC-coupled solar + storage
Where the inverter sits decides your efficiency and upgrade path.
Read →Understand it in five minutes
How solar panels make DC
TED-Ed on the photovoltaic effect.
Inside a lithium-ion cell
Animated look at what moves when you charge.
AC vs DC in plain terms
The difference every tool on this site depends on.
Monthly DC Build Contest
Share your solar shed, van battery or home charger install. Prizes every month.
Enter the contest →Keep 9DC free
Support new calculators, contest prizes and expert writers from $3 a month.
Support 9DC →Write, build, film with us
Electricians, EV nerds, solar installers and developers — we're hiring contributors.
See open roles →Quick answers
Why does DC fast charging slow down after 80%?
As a lithium-ion cell fills, the car's battery management system lowers the current to limit heat and prevent lithium plating, so power tapers. In practice the last 20% can take about as long as going from 10% to 80%. Try it in the fast-charge calculator.
Are solar panels AC or DC?
Panels produce direct current. A string inverter or microinverters convert it to alternating current for your home and the grid. Batteries store DC, which is why where you connect them matters — see DC- vs AC-coupled systems.
Is 12 V, 24 V or 48 V better for an off-grid system?
Higher voltage means lower current for the same power, so thinner, cheaper cable and lower losses. 12 V suits small van and boat systems; 24 V suits mid-size RVs; 48 V is the norm for cabins and homes with inverters above roughly 3 kW.
How accurate are the calculators?
They use widely published engineering assumptions and are good for planning and comparing options. Real results depend on your specific vehicle, roof, climate and equipment — always confirm designs with a qualified professional.
Is 9DC connected to any company called “DC”?
No. “DC” here means direct current. 9DC is an independent educational site, not affiliated with any brand, publisher or government using similar letters. See our trademark disclosure.
The DC Brief
One email every other week: new tools, charging-network changes, price moves in panels and batteries. No spam, unsubscribe anytime.