Inputs
Example data
| Scenario | Inputs | Key outputs |
|---|---|---|
| AGM bank, moderate recharge | 12 V, 200 Ah, 50% DoD, 6 h, 5 A load, 20% margin | Suggested: ~35 A, AC current: ~2.25 A, Output: ~420 W |
| LiFePO4 bank, faster goal | 24 V, 300 Ah, 60% DoD, 4 h, 0 A load, 15% margin | Suggested: ~60 A, AC current: ~7.73 A, Output: ~1,440 W |
| Lead-acid, gentle charging | 48 V, 400 Ah, 40% DoD, 10 h, 10 A load, 20% margin | Suggested: ~40 A, AC current: ~10.31 A, Output: ~1,920 W |
Formula used
How to use
- Pick a chemistry preset close to your battery type.
- Enter your bank voltage and capacity, or use the bank builder.
- Set the depth you want to refill and your target hours.
- Add any DC load that runs while charging.
- Keep a safety margin for heat and aging.
- Review both suggested and time-target charger sizes.
- Use the download buttons to save your results.
Notes
- Real charging profiles vary by charger and battery management settings.
- Lead-acid absorption can extend time beyond the bulk estimate.
- If the time-target size exceeds the chemistry limit, choose longer time.
- Verify wiring, fusing, and thermal limits before installation.
Battery bank sizing inputs
Accurate charger sizing starts with bank voltage and total amp‑hours. Voltage sets the charger output class, while amp‑hours set how much energy must be replaced. If you build the bank from cells, series strings add voltage and parallel strings add capacity. For planning, treat a 12 V 200 Ah bank as 2.4 kWh at 100% depth, but charging usually targets partial refill. Many installers size for daily cycling: DoD often 20–60%. For standby systems, recharge times may be 8–24 hours to limit plate shedding. When capacity is specified at a 20-hour rate, high discharge currents reduce usable Ah, so conservative margins are appropriate. Temperature also shifts charge voltage and acceptance noticeably.
Charging time and current
The calculator converts the desired refill into a required bulk current. Replacing 50% of a 200 Ah bank means 100 Ah before losses. Dividing required amp‑hours by target hours gives a baseline charge current, then any concurrent DC load is added. A safety margin raises the final recommendation to cover heat, cable drop, and aging.
Efficiency and top‑off losses
Real charging is not perfectly coulombic. Battery acceptance and charger conversion losses mean more input is needed than the amp‑hours removed. The overhead factor approximates absorption and balancing time where current tapers. Using 90% battery efficiency and 15% overhead turns 100 Ah into about 127.8 Ah demanded from the charger, tightening the current requirement.
Safe charge rate limits
C‑rate limits protect chemistry and life. The calculator caps the recommendation using Capacity × C‑rate, so a 200 Ah bank at 0.25C limits charge current to 50 A. If your time goal needs more, the warning indicates the goal is aggressive. Options include extending time, adding parallel strings, or selecting a chemistry that supports higher rates.
AC supply and installation checks
Charger output power is V × A. Input power is higher by the conversion efficiency, and input current depends on AC voltage and power factor. These estimates help size breakers and wiring. Final selection should confirm thermal derating, ventilation, cable gauge, fuse coordination, and battery management settings for absorption voltage and cutoffs.
FAQs
1) What if the time-target charger size exceeds the chemistry limit?
Increase recharge time, add capacity in parallel, or choose a higher C-rate chemistry. Staying under the limit reduces heat, improves cycle life, and prevents protective shutdowns in managed packs.
2) Why does the calculator include absorption or top-off overhead?
Near full charge, current tapers while voltage is held. That stage adds time and extra amp-hours due to internal losses, balancing, and temperature effects. The overhead factor approximates those realities for planning.
3) Which amp-hour rating should I use for my bank?
Use the manufacturer’s stated capacity at the standard discharge rate, commonly 20 hours for lead-acid. If your application draws very high currents, derate capacity or increase margin to avoid undersizing.
4) How does a running DC load change the recommended charger?
The charger must supply both charging current and the live load. The calculator adds load amps before applying the safety margin, which prevents slow recharge or overload when devices stay on.
5) How close is the AC input current estimate to real values?
It is a sizing estimate based on output power, efficiency, AC voltage, and power factor. Real chargers may draw peaky current and vary with stage, so always confirm with the charger datasheet and local electrical code.
6) When should I use the bank builder inputs?
Use it when you know the individual battery voltage and amp-hours, plus how many are in series and parallel. The tool computes bank voltage and total capacity automatically, reducing entry mistakes.