What Size RV Converter Do I Need?

Direct Answer

The right size RV converter equals your continuous DC house load plus the charge current your battery bank needs at the same time. A 30A unit suits a small pop-up with one flooded lead acid battery; a 55A unit is the most common upgrade for a standard travel trailer; a 75A or 100A unit is where large fifth wheels and motorhomes with lithium banks often land. The converter sizing calculator runs the math for your exact loads and battery configuration.

This page covers the general sizing method across coach sizes and battery chemistries. It does not work a single deep example for any one battery model. If you have a single 100Ah LiFePO4 bank and want the complete worked calculation, including the exact charge-current figures from the Battle Born BB10012 manual, that detail is on the 100Ah lithium converter sizing page.

Why You Cannot Size a Converter by Shore Power Service Alone

A 30-amp shore power pedestal supplies 3,600 watts of AC power. A 50-amp pedestal supplies up to 12,000 watts. Neither number tells you what size converter you need.

The converter takes one branch of that AC power and converts it to 12V DC. Its output rating is in DC amps, not AC amps. A 55A converter rated at 940 watts draws about 8 amps from a 30A circuit, leaving the rest of the circuit for the air conditioner, microwave, and other AC loads. The converter's DC output is a separate bus entirely from the AC panel.

Sizing a converter is a DC-side problem: you need enough DC output to power your house loads and charge your battery bank simultaneously.

The Two-Part Sizing Formula

Converter output must cover two demands at once:

Part 1: Continuous DC house load. While plugged into shore power, 12V devices draw from the converter's DC bus. These include interior LED lighting, the water pump, vent fans, the propane refrigerator control board, slide-out parking-rest loads, USB chargers, and entertainment systems. On a typical 28-32 foot travel trailer with the usual accessories running, this continuous draw often falls between 15A and 25A. Heavier coaches with more 12V circuits run higher.

Part 2: Battery charge current. Any converter output that is not consumed by house loads flows into the battery as charge current. Your battery manufacturer's documentation specifies the recommended and maximum charge rates for your bank. If house loads are consuming 18A and your converter outputs 45A, the battery receives 27A of charge current. If the battery's published maximum is 30A, that margin is adequate. If the bank is larger and the maximum is 60A, a 45A converter cannot deliver a full charge rate while house loads are running.

The formula is straightforward:

Required converter output = Continuous DC house load + Target battery charge current

The nuance is in what "target charge current" means for your battery chemistry.

How Battery Chemistry Changes the Math

Different battery types accept charge current at different rates. Getting this wrong in the direction of too small means chronic undercharging. Getting it wrong in the direction of too large triggers the battery's protection circuitry.

Flooded Lead Acid (FLA)

FLA batteries accept charge current at a recommended rate of roughly 10 to 13 percent of their amp-hour capacity. This is an industry guideline from battery engineering practice, not a single manufacturer figure. A 200Ah FLA bank charges well at 20 to 26A delivered to the battery. FLA batteries also need periodic equalization at a higher voltage (typically 15.0 to 15.5V for 12V systems), which requires a converter that supports equalization mode. FLA batteries tolerate multistage charging well, and converter output current above the recommended rate is handled by the battery's chemistry up to its stated maximum, but prolonged overcharging accelerates water loss and plate damage.

For a 200Ah FLA bank with 18A of house loads, the sizing calculation is: 18A loads plus 26A charge current equals a 44A requirement. A 45A converter covers this with minimal margin; a 55A converter gives comfortable headroom.

AGM (Absorbed Glass Mat)

AGM batteries accept higher charge rates than FLA, typically 20 to 30 percent of capacity, and many manufacturers specify the exact maximum in their documentation. AGM does not require equalization and does well with standard multistage converter profiles. A 200Ah AGM bank can accept 40 to 60A of charge current without harm, depending on the manufacturer's specification for that model. This means a larger converter is justified and effective, not wasteful.

For a 200Ah AGM bank with 18A of house loads: 18A plus 50A charge current equals a 68A requirement. A 75A converter covers this and still has margin for load spikes.

LiFePO4 (Lithium Iron Phosphate)

LiFePO4 batteries accept higher charge rates, typically 0.5C (50A for a 100Ah bank, 100A for a 200Ah bank), and in some cases higher, but the exact figures vary by brand and model. The battery's Battery Management System (BMS) enforces the limit automatically: if charge current exceeds the battery's maximum, the BMS disconnects the charge circuit. Repeated BMS disconnects are unnecessary stress on the system. Always size so that the charge current delivered to the battery stays within the manufacturer's published maximum for that specific model.

LiFePO4 also requires a converter whose maximum output voltage reaches the absorption target the battery specifies, typically 14.2 to 14.6V. A legacy lead-acid-only converter that tops out at 13.6V cannot fully charge a LiFePO4 bank regardless of its amperage rating. Voltage profile compatibility matters as much as output current for lithium. The converter must support a two-stage lithium charging profile or have a selectable lithium mode.

For the complete worked example on a single 100Ah LiFePO4 bank, including exact charge-current figures from a manufacturer manual, see What Size Converter for a 100Ah Lithium Battery?. That page is the right starting point if that is your exact configuration.

For lithium retrofit planning across multiple battery sizes and coach types, continue with the method below, then verify your specific battery's spec sheet.

Output Tiers by Coach Size

The following table maps coach type to common converter output ranges. These are editorial guidance based on typical DC loads and common battery bank sizes for each class, not manufacturer requirements. Your actual loads may differ. Use the converter sizing calculator to run your specific numbers.

These output tiers reflect common WFCO and Progressive Dynamics product lines. WFCO's WF-8900 AD series spans 35A through 75A in the auto-detect lithium configuration (models WF-8935-AD through WF-8975-AD). Progressive Dynamics' current PD9300 series offers 30A, 45A, 60A, and 80A models, all with selectable LiFePO4 profile support. Model numbers and output sizes verified from manufacturer product documentation.

Why Charge Profile Matters as Much as Amperage

A converter with the right amperage but the wrong voltage profile will undercharge your batteries every time you plug in.

For lead acid and AGM batteries, standard multistage profiles (bulk, absorption, float) are widely supported. The key voltage targets are bulk at 14.4V, absorption at 14.4-14.8V depending on chemistry, and float at 13.2-13.6V for lead acid. Most current converters handle this correctly.

For LiFePO4, the profile requirements are different:

1. The converter must reach the battery manufacturer's specified absorption voltage, which is typically 14.2 to 14.6V. A converter that tops out at 13.8V cannot complete a full charge cycle.
2. The converter must not apply a continuous high-voltage float above the battery manufacturer's maximum float voltage. Many LiFePO4 batteries do not require active float at all; a two-stage profile (bulk followed by a rest at the absorption voltage) is correct.
3. The converter's charging algorithm should respect a low-temperature charge lockout if your battery's BMS enforces one. Attempting to charge a LiFePO4 battery below freezing can cause lithium plating, a safety risk. Never attempt to defeat or bypass the BMS to restore charging. If the BMS has disconnected due to temperature, the correct response is to allow the battery to warm before resuming charge.

WFCO's WF-8900 AD series uses auto-detect technology to sense battery chemistry at startup and apply the appropriate profile automatically. In lithium mode, the product sheet specifies bulk charge voltage of 14.6V DC and output voltage range of 13.6 to 14.6V DC for lithium. This data is sourced from WFCO's WF-8900 AD product sheet, which covers all five models in the series (WF-8935-AD through WF-8975-AD).

Progressive Dynamics' PD9300 series uses a user-selectable chemistry switch to choose between FLA, AGM, LiFePO4, or a fixed 13.6V output. Output voltage range is 13.2 to 14.7V DC across all PD9300 models, per the PD9300 owners manual. This range accommodates LiFePO4 absorption targets. The user must set the chemistry selection before connecting the battery, per the PD9300 manual caution.

Note on the earlier PD4600 series: the PD4635, PD4645, and PD4655 converters support LiFePO4 charging only after an internal jumper is set by a qualified technician. They do not auto-detect or have a user-facing switch. Do not assume LiFePO4 compatibility on a PD4600 without verifying the jumper has been correctly configured per the PD4600 owners manual. The PD4600 is an older design; the PD9300 series is the current replacement.

When to Upsize Beyond the Basic Formula

The two-part formula gives the minimum adequate size. Several conditions justify going one step larger:

You are adding batteries now or soon. A 45A converter paired with a single 100Ah FLA battery is adequate today. Add a second 100Ah battery without upsizing the converter, and the charge time nearly doubles. If expansion is planned, size the converter for the final configuration now.

You run heavy loads while charging. The formula uses a continuous DC load estimate. If you run a 12V refrigerator, multiple fans, and interior lighting simultaneously, your continuous load is at the top of the range, not the bottom. Use measured or conservatively estimated load values, not minimum estimates.

Your shore power sessions are short. If you typically have only a few hours plugged in before a travel day, a larger converter recovers the battery faster. A 30A converter on a 200Ah bank that is 50 percent discharged will take many hours to reach full charge; a 55A unit does it in roughly half the time, because more of the output reaches the battery after house loads are subtracted.

You are retrofitting lithium. LiFePO4 batteries accept much higher charge rates than lead acid, so the old undersized lead-acid-era converter becomes a bottleneck. An RV that shipped with a 30A or 45A converter may need a 55A or 75A unit after a lithium retrofit to take advantage of the battery's faster charge acceptance. Check the specific battery's charge current specification before selecting a converter.

A Note on Converter Efficiency

Converter output ratings are at the DC terminals. The converter is not 100 percent efficient; it draws more AC power from the branch circuit than it delivers as DC. Neither WFCO nor Progressive Dynamics publishes an efficiency figure for these converters, so treat any single number you see quoted elsewhere with suspicion. What the published figures do support is an editorial calculation: the WFCO WF-8955-AD product sheet lists 940W power input and 55A output, and 55A at a 13.6V normal-mode output is about 748W delivered, which works out to roughly 79 percent under steady-state load. That is our arithmetic from the manufacturer's own input and output numbers, not a manufacturer efficiency rating. The efficiency gap is dissipated as heat, which is why converters have ventilation requirements and should never be mounted in an enclosed airless space.

For converter sizing purposes, this efficiency factor is already baked into the output ampere ratings the manufacturers publish. Size to the DC amp output figure, not to a derived AC input figure.

Safety Checklist Before Sizing

Before selecting a converter, confirm:

• Your battery manufacturer's recommended and maximum charge current for your specific model and bank size. This is in the battery manual or spec sheet.
• Your battery manufacturer's required absorption and float voltages. These must be within the converter's output range.
• The chemistry-select capability of any converter you consider. Not all converters support all chemistries. Verify for the exact model, not just the product family.
• UL 458 listing on any converter installed inside an RV. The RV Industry Association requires listed equipment for RV compliance. Both WFCO and Progressive Dynamics maintain UL and cUL listings on their current product lines per their product documentation.
• Shore power service class (30A versus 50A) determines the AC input requirements of any converter or inverter-charger you install, but does not determine DC output size.

Use the Calculator for Your Specific Numbers

The sizing guidance in this article is a framework, not a prescription. Every coach is different, and load estimates vary widely. The RV converter sizing calculator lets you enter your actual DC appliance loads and battery bank size and returns a recommended output range with the math shown. Run the calculation before committing to a converter size.

If you are comparing lithium-compatible converters specifically, the best RV converters for lithium batteries page covers models verified for LiFePO4 compatibility with sourced specs.

Frequently Asked Questions

Can I use a larger converter than the formula requires?

Yes, within reason. A converter rated above the target does not harm the battery, because the battery's BMS (for lithium) or chemistry (for lead acid) limits how much current it will accept. The excess capacity is simply unused. The practical limit is cost and physical size. For LiFePO4 batteries, avoid sizing so large that you expect to deliver more charge current than the battery's published maximum: the BMS will disconnect, not quietly accept the overload.

Does a 50-amp RV need a bigger converter than a 30-amp RV?

Not necessarily. Shore power service affects the AC circuits, not the DC converter size. A 50-amp coach with a modest battery bank and light DC loads may still use a 45A or 55A converter. The battery bank size and DC load profile drive converter sizing, not the shore power rating.

What happens if my converter is too small?

An undersized converter means your house loads consume most of the output, leaving little or nothing for battery charging. The battery slowly discharges even while plugged in, especially if the loads are heavy. Over time, repeated deep discharge shortens battery life. If the converter is so undersized that house loads exceed its output rating, the converter may overheat or trigger an internal protection circuit.

What is the difference between a converter and an inverter-charger?

A converter takes AC power from shore power and produces DC. An inverter-charger does the same in converter mode, but also inverts DC battery power to AC when shore power is absent. Inverter-chargers are common in high-end rigs and lithium retrofits because they provide both functions in one unit. For sizing purposes, the DC output amperage of an inverter-charger in charging mode is evaluated the same way as a standalone converter.

Do I need a lithium-specific converter, or can I use a lead acid converter with a LiFePO4 battery?

You need a converter that can reach the absorption voltage your LiFePO4 battery requires, typically 14.2 to 14.6V, and that does not apply a continuous float voltage above the battery's maximum. Most modern converters with a selectable or auto-detect lithium mode meet these requirements. A legacy lead-acid-only converter that tops out at 13.6V does not, and will leave the battery chronically undercharged. Verify the specific model's voltage range against your battery manufacturer's spec sheet.

How do I find my actual DC house load?

The most reliable method is a clamp meter reading on the DC distribution bus while the coach is plugged in and all typical loads are running. If you do not have a clamp meter, add up the rated current draws of each 12V device from their labels or manuals, then apply a usage factor (LED lighting is typically 30 to 60 percent on continuously; the water pump is intermittent). The converter sizing calculator includes a guided load-entry form if you prefer to work through it appliance by appliance.

Sources

• WFCO WF-8900 AD Series Product Sheet (NEW-8900-Product-Sheet.pdf) WFCO manufacturer product sheet covering all five WF-8900 AD models (WF-8935-AD through WF-8975-AD). Proves: output current per model (35A, 45A, 55A, 65A, 75A), lithium output current (32.5A, 41.5A, 50A, 60A, 70A), input voltage 105-130V AC/60Hz, voltage output range Lead Acid 13.2-14.4V DC / Lithium 13.6-14.6V DC, bulk charge mode Lithium 14.6V DC, UL and cUL listed and FCC Class B compliant. Retrieved via web search from wfcotech.com hosted PDF. Authority tier: manufacturer product sheet. Verified 2026-09-23.
• WFCO WF-8935-AD Power Center Product Page WFCO manufacturer product page for the WF-8935-AD 35-amp auto-detect power center. Confirms output current 35A, lithium voltage output 13.2-14.6V DC, converter type three-stage (lead acid) / two-stage (lithium), input 105-130 VAC 60 Hz. Authority tier: manufacturer product page. Verified 2026-09-23 (confirmed live via web search returning page content).
• WFCO WF-8955-AD Power Center Product Page WFCO manufacturer product page for the WF-8955-AD 55-amp auto-detect power center. Confirms output current 55A (50A in lithium mode), bulk mode 14.4V DC, absorption mode 13.6V DC, float mode 13.2V DC, output power 940W, voltage output lithium 13.2-14.6V DC. Authority tier: manufacturer product page. Verified 2026-09-23 via web search returning full spec table.
• Progressive Dynamics PD9300 Series Product Page Progressive Dynamics manufacturer product page for the PD9300 converter series. Confirms available models: PD9330 (30A), PD9345 (45A), PD9360 (60A), PD9380 (80A). Confirms selectable chemistry support for FLA, AGM, LiFePO4, and fixed 13.6V output. Confirms the PD9300 replaces PD9100 and PD9200 series. Authority tier: manufacturer product page. Verified live 200 OK 2026-09-23.
• Progressive Dynamics PD9300 Series Owners Manual (English) Progressive Dynamics owners and installation manual for the PD9300 series. Proves output voltage range 13.2-14.7V DC for all four models (PD9330, PD9345, PD9360, PD9380). Also proves rated output current per model: PD9330 30A / PD9345 45A / PD9360 60A / PD9380 80A. Proves the caution to select chemistry before connecting the battery. Authority tier: manufacturer manual. PDF verified live 200 OK 2026-09-23.
• Progressive Dynamics Power Converters Product Lineup Progressive Dynamics converter lineup page. Confirms PD4600 series (PD4635, PD4645, PD4655) and their LiFePO4 jumper documentation. Confirms PD9100L (LFP) series models (PD9130LV, PD9145ALV, PD9160ALV, PD9180ALV) as prior dedicated lithium converters, now superseded by PD9300 multi-chemistry. Confirms PD9300 as the current replacement for PD9100 and PD9200. Authority tier: manufacturer product page. Verified live 200 OK 2026-09-23.
• Progressive Dynamics PD4600 LiFePO4 Jumper Settings Document Progressive Dynamics technical document for PD4600 series LiFePO4 jumper configuration. Supports the statement that PD4600 series converters require an internal jumper set by a qualified technician for LiFePO4 compatibility, and do not auto-detect or have a user-accessible switch. Authority tier: manufacturer installation document. Referenced from the manufacturer lineup page. Verified linked from official progressivedyn.com 2026-09-23.
• RVIA Recognized Listing Agencies Page RV Industry Association page on listing agency requirements. Confirms that RVIA member manufacturers are required to install listed equipment in RVs, and that UL LLC is a recognized listing agency. Supports the claim that UL 458 listing is a relevant safety certification for RV converter/chargers. Authority tier: industry standards body. Verified live 2026-09-23.

Published 2026-09-23. Electrical specifications are model-specific: confirm every figure against the manual for your exact equipment before acting on it.