---
title: ESP32-S3 Arduino Wi-Fi HTTP downloads crawl at about 1 KB/s
date: 2026-06-14
summary: HTTP(S) downloads to SD from an ESP32-S3 Arduino sketch (M5Stack Cardputer-ADV) ran at about 1 KB/s. The cause was Wi-Fi modem power-save. Calling WiFi.setSleep(false) after connecting raised it to about 85 KB/s.
tags: esp32, arduino, wifi, m5stack, cardputer
environment: M5Stack Cardputer-ADV (ESP32-S3, no PSRAM); Arduino via PlatformIO, platform espressif32@6.9.0 (ESP-IDF 4.4); HTTP(S) downloads written to microSD
author: shaun, written up with Claude
status: published
---

## Symptoms

An Arduino MP3 player sketch on an M5Stack Cardputer-ADV downloads MP3 files over Wi-Fi
and writes them to the microSD card. Throughput was about **1 KB/s**.

## Root cause

Wi-Fi **modem power-save**. Turning it off was the only change needed, which is how it
was identified.

Background (general ESP32 behaviour, not separately measured here): in station mode the
ESP32 Wi-Fi driver uses modem sleep by default, so the radio dozes between access-point
beacons. That is fine for occasional small requests but throttles a long bulk download.

## Fix

Turn modem sleep off once the station is up:

```cpp
#include <WiFi.h>

WiFi.mode(WIFI_STA);
WiFi.begin("your-ssid", "your-wifi-password");
while (WiFi.status() != WL_CONNECTED) delay(100);
WiFi.setSleep(false);   // disable modem power-save
```

With this one change, downloads went from about 1 KB/s to about **85 KB/s**, and the files
were verified byte for byte.

Caveat (not measured here): with sleep off the radio stays awake, so expect higher current
draw while Wi-Fi is on. On a battery device, turn Wi-Fi off when the transfer is done.