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Open Roads Forum  >  Class C Motorhomes  >  Class C

 > Generator/Shore Power Work, Battery Power Doesn't

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whemme

Spencer, IA

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Posted: 07/27/20 05:58am Link  |  Quote  |  Print  |  Notify Moderator

BrocNeal,

Andy with PD sent me an email this morning and unfortunately he had already shipped the charger board to me. So, send me your real name and shipping address and I will reship it to you after I receive it. You can contact me via PM (private mail) with that info if you prefer.


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Posted: 07/27/20 07:21am Link  |  Quote  |  Print  |  Notify Moderator

This is the most awesome thread I've read on here in a while. Please continue to update it!


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whemme

Spencer, IA

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Posted: 07/28/20 09:23pm Link  |  Quote  |  Print  |  Notify Moderator

BrocNeal, well your replacement battery charger PC board is on the way to you. Sure hope this fixes the no charging problem. If not the only other thing that I can think of is a failure of the S.C.R. as shown on pages 3, 17 & 20 of the Service Manual. I can believe that this component may have been destroyed if as you said the former owner of your rig connected up the house battery(s) reversed polarity. The SCR is mounted in a heat sink as shown on page 17 in the transformer module. Leads to it would have to be unsoldered and then the part would then have to be unbolted to remove it. Then hopefully the SCR has brand and P/N on it in order to purchase a replacement.

BrocNeal

Utah

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Posted: 07/28/20 09:30pm Link  |  Quote  |  Print  |  Notify Moderator

whemme wrote:

BrocNeal, well your replacement battery charger PC board is on the way to you. Sure hope this fixes the no charging problem. If not the only other thing that I can think of is a failure of the S.C.R. as shown on pages 3, 17 & 20 of the Service Manual. I can believe that this component may have been destroyed if as you said the former owner of your rig connected up the house battery(s) reversed polarity. The SCR is mounted in a heat sink as shown on page 17 in the transformer module. Leads to it would have to be unsoldered and then the part would then have to be unbolted to remove it. Then hopefully the SCR has brand and P/N on it in order to purchase a replacement.

That's what I'm hoping, I don't know if it'd fix the no lights when hooked up to shore power but I hope so. I know I called progressive dynamics and that was what the guy said he would think the problem would be after I told him my issues, so let's hope for the best!
Now what exactly is the SCR and what does it do? It sounds complicated but the motorhome is from 1979 so I wouldn't think it would be too crazy!

whemme

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Posted: 07/29/20 12:16pm Link  |  Quote  |  Print  |  Notify Moderator

BrocNeal,

OK, look at the schematic on page 20 of the maintenance manual. You will notice the SCR in the upper left corner of the schematic. The SCR acts like an electronic on/off switch. How the system works is that the battery charger PC board monitors the charge level of the house battery(s) by inputting the current battery voltage level onto the red wire going into the board. The board analyzes this voltage level and determines if further charging of the battery(s) is necessary, If so, the board sends a signal to the SCR's gate terminal via the green wire shown which then turns on the SCR connecting the output of the DC voltage output of the transformer module via the blue wire shown into the SCR and since the SCR is now turned on the SCR now conducts that DC voltage to the output terminal of the SCR which connects to the battery9s) via the orange wire.

Actually, the SCR is never fully turned off. The charge board varies the signal to the SCR gate via the green wire on a pulse basis with the turn on pulse being longer when the battery(s) are heavy discharged to a turn on pulse being shorter when the batter(s) are fully charged and only requiring a low level maintenance charge level.

If this SCR was destroyed when the former owner connected up the battery(s) reversed polarity, of course the charge board would be trying to turn on the SCR to try and make it conduct a charge current to the battery(s) to no avail.

* This post was edited 07/30/20 12:37pm by whemme *

BrocNeal

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Posted: 08/06/20 08:04pm Link  |  Quote  |  Print  |  Notify Moderator

whemme wrote:

BrocNeal,

OK, look at the schematic on page 20 of the maintenance manual. You will notice the SCR in the upper left corner of the schematic. The SCR acts like an electronic on/off switch. How the system works is that the battery charger PC board monitors the charge level of the house battery(s) by inputting the current battery voltage level onto the red wire going into the board. The board analyzes this voltage level and determines if further charging of the battery(s) is necessary, If so, the board sends a signal to the SCR's gate terminal via the green wire shown which then turns on the SCR connecting the output of the DC voltage output of the transformer module via the blue wire shown into the SCR and since the SCR is now turned on the SCR now conducts that DC voltage to the output terminal of the SCR which connects to the battery9s) via the orange wire.

Actually, the SCR is never fully turned off. The charge board varies the signal to the SCR gate via the green wire on a pulse basis with the turn on pulse being longer when the battery(s) are heavy discharged to a turn on pulse being shorter when the batter(s) are fully charged and only requiring a low level maintenance charge level.

If this SCR was destroyed when the former owner connected up the battery(s) reversed polarity, of course the charge board would be trying to turn on the SCR to try and make it conduct a charge current to the battery(s) to no avail.

Okay that makes sense. I'll have to look a little more into that. I just got home from a vacation so that's why I haven't been on here. I did have a chance to crawl underneath the motorhome and didn't find any fuses or circuit breakers. I did redo some grounds because they looked pretty rough. Still no luck on fixing the problem. I dont remember if I already said this, but I got an outlet tester and plugged it in to every outlet when plugged in to shore power/generator and they all say "Hot/Neutral Reversed". So I assume that definitely is part of my issue. I dont know what that means but its good to know. Still doesn't make any sense that the lights would work when I brought it home and then I change out the circuit breakers in the house battery box and get the lights working off the battery that the issue would reverse into what it is now. But I'll get it, there's only one way to learn!

whemme

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Posted: 08/07/20 09:14am Link  |  Quote  |  Print  |  Notify Moderator

BrocNeal,

OK I guess I can assume the replacement charger board did not fix the problem. Your system may have only one SCR or maybe two SCRs wired in parallel. A SCR is a 3 terminal device, an input terminal (anode), an output terminal (cathode) and a gate terminal. When connected to shoreline power, measure the DC voltage to ground on all three SCR terminals. The output terminal should be the same as your house battery voltage, 12.48 volts per a previous measurement you made. The voltage at the input terminal should be I believe around 18 volts, the same as the output voltage from the transformer module you previously measured. The voltage on the gate terminal will tell the story. If it is more than 1.0 volt higher than the SCR’s output terminal, then that or both SCRs are toast.

* This post was edited 08/07/20 10:22pm by whemme *

BrocNeal

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Posted: 08/11/20 11:01pm Link  |  Quote  |  Print  |  Notify Moderator

whemme wrote:

BrocNeal,

OK I guess I can assume the replacement charger board did not fix the problem. Your system may have only one SCR or maybe two SCRs wired in parallel. A SCR is a 3 terminal device, an input terminal (anode), an output terminal (cathode) and a gate terminal. When connected to shoreline power, measure the DC voltage to ground on all three SCR terminals. The output terminal should be the same as your house battery voltage, 12.48 volts per a previous measurement you made. The voltage at the input terminal should be I believe around 18 volts, the same as the output voltage from the transformer module you previously measured. The voltage on the gate terminal will tell the story. If it is more than 1.0 volt higher than the SCR’s output terminal, then that or both SCRs are toast.


No it didn't unfortunately. So im working on pulling the converter box out so I can check the SCR and everything. That's turned out to be quite the job but I'll get it. Once I get that out I'll be able to test it much easier than where its currently at. If the SCR is bad, is that something you can replace easily? Like just go buy a new one or do I have to find this exact same one or do I then need to find a replacement box as a hole? It looks intimidating not gonna lie.

whemme

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Posted: 08/12/20 08:33am Link  |  Quote  |  Print  |  Notify Moderator

BrocNeal,

Can you tell if there is just one SCR or two wired in parallel? If you can get one of the SCRs removed, look at the identification markings ( brand & P/N) on it. Should then be able to buy replacements.

But first get the voltage readings on the 3 terminals of one of the SCRs so that it can be determined if they are really bad.

whemme

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Posted: 08/12/20 09:40am Link  |  Quote  |  Print  |  Notify Moderator

Click on the following link to see what the SCR(s) in your power center look like physically. This is probably not the actual SCR you may need but shows you what they look like. A thyrister is the same as a SCR. Typical SCR

The small terminal is the gate, the large terminal on the top is the anode and and body of the SCR is the cathode terminal.

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