30/10/2026
𝐓𝐡𝐞 𝐀𝐂 𝐑𝐢𝐩𝐩𝐥𝐞 𝐓𝐞𝐬𝐭: 𝐓𝐡𝐞 𝟐-𝐌𝐢𝐧𝐮𝐭𝐞 𝐀𝐥𝐭𝐞𝐫𝐧𝐚𝐭𝐨𝐫 𝐂𝐡𝐞𝐜𝐤 𝐄𝐯𝐞𝐫𝐲 𝐀𝐮𝐭𝐨 𝐄𝐥𝐞𝐜𝐭𝐫𝐢𝐜𝐢𝐚𝐧 𝐒𝐡𝐨𝐮𝐥𝐝 𝐁𝐞 𝐃𝐨𝐢𝐧𝐠
This one is for the auto electricians.
An alternator generates AC current internally, which is converted to DC by the rectifier diodes. When a diode starts failing, AC current leaks into the charging system. This is known as AC ripple.
Why does it matter?
Modern vehicles rely on stable DC voltage. Excessive AC ripple can cause intermittent faults in battery management systems, ECUs, transmission controllers, and other sensitive electronics, often leading to misdiagnosis.
✅ How to test: • Set your multimeter to AC voltage
• Test across the battery terminals with the engine running
• Switch on major electrical loads
Results: ✔ Below 50mV AC = Healthy
⚠ 50-100mV AC = Early diode wear
❌ Above 100mV AC = Likely diode failure
The important part? An alternator can still show 14.2V DC and pass a standard charging test while failing an AC ripple test.
Before signing off any alternator job, take two minutes and check the AC ripple. It could save a comeback later.
📍 HDM Auto Electrical Parts | Boksburg | Pretoria | Vanderbijlpark
💬 Do you run the AC ripple test as standard? Let us know in the comments.
