Recently was handed a failed 50A 12V Charger (SEC-1250) out of an RV ... as it has now been replaced with a new one, this Charger is destined for ETrash ... this unit was apparently plugged in to a RV GenSet which had also failed ... most charger failures from my experience, fail on the Battery side of the circuit, this particular unit was charred right after the RFC filter with the remainder of the unit looking pristine ... found 2 CHARRED (look identical) components mounted in parallel (side by side) and in series with the final stage of the AC RFC filter which directly drive the HIGH Voltage Bridge per my doodle below

Device 1
L --- fuse ---- inductor ---------- --- ~ Bridge
| | Device 2
cap cap
| |
N --------------- inductor ------------------------- ~ Bridge


These devices were dipped in a hard black coating and are about the diameter of a dime with the approximate thickness of 2 nickels ... my first thought was they were MOV's (Varistors) however, being they are in a series configuration between the RFC and Bridge it is more likely they are some kind of over current and or thermal protection device ... as both the board and these components are charred beyond recognition, there is no way to discover what they were from their remains. In order to source 600W, and being these devices are in parallel, they were probably each expected to supply 300W max ... with a suspected overvoltage failure from the GenSet, if either one of these failed, it's sister device would certainly be soon to follow because neither would be expected to handle a full 600W load.

Any thoughts on what these devices might actually be? ... I am thinking of bypassing these temporarily to determine if the remainder of the charger still functions before surrendering this unit to ETrash. A 12V 50 Amp bench supply would be a welcome addition to my workshop so replacing the factory designed components would be preferable, providing there isn't more major issues with the unit. I just looked at a supplier catalog and Thermistors were only listed up to 40 watts (no where near 300W) plus much thicker then these devices.

Thanx in advance for any suggestions

 

Are the inductors in the schematic actually the transformer primary? Is the power input to the circuit on the left side or the right side of the schematic?

 

If they are in series with mains input then they could be NTCs intended to limit inrush current.
https://en.wikipedia.org/wiki/Inrush_current_limiter

 

Thank you. I see it now. I misread the bridge connections -maybe need to start wearing my glasses.

 

Sorry seems doodles don't translate well on posted version

nodes:
1) L to Fuse
2) Fuse to C1(pin1) and L1(pin1)
3) L1(pin2) and C2(pin1) to Dev1 (pin1) and Dev2(pin1)
4) Dev1(pin2) and Dev2(pin2) to Bridge(pin1)

5) N to C1(pin2) and L2(pin1)
6) L2(pin2) and C2(pin2) to Bridge(pin4)

 

Well, that excludes NTC then, 'cos you wouldn't put two in parallel with each other like that, though it is just the place for one of them.
The only thing I can think of that makes sense is that they are resistors but if they are disc shaped then that is unlikely.

Do they like this (except black)?

 

Update ... With these components bypassed the Power Supply appears to be working

To source 600W, each of these devices must be able to handle 2.5A at 120VAC ... Assuming a NTC (ICL) device rated at 2.2 ohms, each device would have to be able to dissipate up to 14W of heat ... understand these devices were side by side (no separation) up against one of the 1uF poly Caps and the iron core of the Filter Inductors ... 14W * 2 with no heat sink, even with a fan (which isn't on all the time) might explain the reason for this failure ... the failure melted the original Cap, there was very little left of the 2 devices (mostly charred ash), AND 2 square inches of copper foil on both top and bottom of the board were charred, fiberglass blackened and foil separated from the board

Well, that excludes NTC then, 'cos you wouldn't put two in parallel with each other like that, though it is just the place for one of them.
The only thing I can think of that makes sense is that they are resistors but if they are disc shaped then that is unlikely.

Do they like this (except black)?
View attachment 129882

Yes there was a small portion of gloss black (looking like the original coating) left on a portion of both devices

 

Just read a spec sheet for ICLs and one of the important WARNINGS for these devices is that they can get VERY HOT and require ample separation from other components (no separation here) ... another important WARNING is care must be taken so these devices are not scratched or touched (like Halogen bulbs, the grease from our hands can compromise the device) ... perhaps that explains why I have seen TLCs in Heat shrink in other products ... the main bus fuse did NOT blow from this failure, considering it takes a substantial amount of heat to burn fiberglass, this failure still occurred without exceeding the FUSED current.