Thunder DCDC charger.
Submitted: Monday, Sep 13, 2021 at 09:57
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Genny
Stevo_62 wrote "Just installed 20A Thunder dc-dc charger in tub of Dmax to charge 2nd battery which runs fridge. When I start vehicle it flashes 0%, 80%, 88% then 100% for about 3 minutes and display turns off, no lights. Is this normal or do I have a problem? Manual doesn't seem to provide answer"
Thread has been archived, but I think I have a definitive answer.
Your wiring from alternator/crank battery to DCDC is not heavy enough. The manual specifies minimum gauges of wire for distance from DC source to charger.
I got one of these put in my camper trailer by a professional auto-electrician. The trailer's existing wire from Anderson plug to batteries was 8g wire, and old mate just tapped into that. My charger did exactly what Stevo_62 described.
I replaced the 8g with 6g as specified in the manual for distance needed in my instance.
Problem solved.
I believe with lighter gauge wire, the initial voltage is sufficient to wake the charger, but once current starts, the voltage drops below the required threshold.