[ Internal components · 5 min read ]
70 A coupling relay burnt inside the Elektroblock
The 70 A relay that connects the starter battery with the auxiliary one during driving charging is the component that fails most often in Schaudt Elektroblock units. It buzzes, sticks or stays open: three symptoms, one culprit. Here's when to replace it and how much it costs.
What this relay does
The Song Chuan 897-1AH-C1 is a sealed power relay with 12 V DC coil and 70 A contacts rated at 14 V DC. Inside the Elektroblock it serves one purpose: when the engine runs and the alternator D+ signal is high, it energises and physically connects the starter battery with the auxiliary one so both charge in parallel from the alternator.
When the engine stops and the D+ signal drops, the relay opens and the two batteries decouple. This prevents the living area from draining the starter battery.
The three failure modes
1. Buzzing coil. The relay vibrates at mains frequency when energised. The coil has partial shorted turns and can no longer hold the armature steady. Audible as a continuous metallic buzz coming from the EBL when the engine runs. Charging still happens (sometimes) but relay life is seconds away.
2. Stuck contacts. The 70 A contacts have welded together from an inrush spike. The relay stays closed even with the engine off, which means the living area drains the starter battery overnight. Diagnosis: with the engine off and the key out, measure continuity between starter and auxiliary battery positives — if there’s continuity, the relay is stuck closed.
3. Open contacts. The contacts have burnt and no longer close reliably. The auxiliary doesn’t charge while driving but charges normally on 230 V mains. The coil may energise correctly but the mechanical connection fails.
How to test it with a multimeter
With the EBL removed and the capacitors discharged safely:
- Coil resistance: between the two coil terminals, in ohms. Expected: 70-90 Ω. Zero or infinite = coil failure.
- Contact resistance (relay energised with external 12 V on the coil): between the two power terminals, in diode mode. Expected: close to 0 Ω. Several ohms = burnt contacts.
Replacement
The relay is through-hole mounted on the EBL’s power board. Component cost is around €15-€20. Board-level replacement needs a temperature-controlled soldering iron (minimum 40 W) and solder-wick for the four or five large pins.
Workshop repair including part, labour, 24-hour bench test and warranty: €90-€120.
Related guides
- Auxiliary battery not charging — complete charging-fault matrix.
- Alternator D+ signal missing — when the coupling command never arrives.
- Internal fuse blows — if the fuse keeps going after replacing the relay.
Read next
Other related faults.
Charging diagnosis
Elektroblock not charging the auxiliary battery
If your Schaudt Elektroblock has stopped charging the living-area battery —neither from 230 V mains, nor from the alternator, nor from the solar panel— the fault is almost always in one of these seven points. This guide shows you how to diagnose which before dismantling anything.
Read guide →
Signal diagnosis
Alternator D+ signal not reaching the Elektroblock
Your motorhome charges perfectly on 230 V mains but when driving on the road the auxiliary battery doesn't go up. The problem is almost always the alternator D+ signal not reaching the Elektroblock. Here's the 10-minute diagnosis.
Read guide →
Internal components
The Elektroblock internal fuse keeps blowing
You replace the T 3.15 AT glass fuse inside the Elektroblock and seconds later it blows again. This is the clearest sign the problem isn't the fuse but what sits behind it: a damaged rectifier or power transistor. Here's the correct diagnosis.
Read guide →
Next step
Time to repair? Free diagnosis by WhatsApp.
Send me the exact Elektroblock model and a photo of the LT panel. I'll confirm whether it's a common fault, the indicative price and how to pack it.
Message on WhatsApp