Jump to content

Blown fuse to isolator


BobBeery

Recommended Posts

You could start with a load tester on the coach battery tune to maximum smoke and see what the meter read just before it caught fire.

Link to comment
Share on other sites

Not sure what you mean.  What should catch fire?  I have a 0-500 amp carbon-pile load-tester and use it often to test batteries and circuits.  I can put a 300 amp load on my "house" battery and all that happens is it goes dead. At 300 amps - it will stay at 9 volts for around 8 seconds and then start to drop. Only "smoke" is coming out of the adjustable carbon resistor.

Link to comment
Share on other sites

On 9/14/2016 at 8:32 PM, Maineah said:

OK prove it with out setting fire to it. It will not carry 60 amps for more than a few seconds. 

Here is a test that proves that 18 feet of 10 gauge wire carried 60 amps pretty easy.   If you don't believe the photos, I suggest trying the test yourself.

Note that I did this first with a battery and a carbon-pile load-tester.  Ran 60 amps for almost 4 minutes before the 50 amp fuse blew.  Wire was warm but not hot yet.

I later hooked a discharged battery via that same 18 feet of wire to the alternator on my 1988 Toyota, hooked with a 30 amp fuse.   Battery was 11.9 volts at the start of the test.  I started the Toyota and ran for 60 seconds and all was fine.  I revved the engine up to 2000 RPM and the fuse blew.   Again, if you don't like my test and don't believe it - do your own test.  I hated cutting off 18 feet of wire from my 500 foot reel, just for this silly test.

1.jpg

IMG_20160916_152527622.jpg

IMG_20160916_152703003.jpg

IMG_20160916_152919824.jpg

IMG_20160916_153216956.jpg

Link to comment
Share on other sites

You were just on the border line at 50 amps of setting the insulation on fire. Good test of a purely resistive load.

Link to comment
Share on other sites

Well that should settle things. JDE you have a chunk of 2 or4ga to test for the cause?

Link to comment
Share on other sites

11 hours ago, Maineah said:

You were just on the border line at 50 amps of setting the insulation on fire. Good test of a purely resistive load.

Hey - it is you that mentioned using a load-tester.  Like I predicted, no test is going to keep you from complaining.  I said early-on that 10 gauge can carry 55 amps in short runs.   This test, with 18 feet of wire is NOT a short run.   Also note that the test with the discharged battery hooked to the alternator is not just a "purely resistive" load. It is a real-world test with a discharged type 24 DC battery.  It proves a discharged battery can blow a 30 amp AGC30 fuse pretty easy.

Link to comment
Share on other sites

9 hours ago, WME said:

Well that should settle things. JDE you have a chunk of 2 or4ga to test for the cause?

My Minicruiser is wired with #2 copper from the front isolator-relay, to the back pair of house batteries.  I did not do that just for better battery charging. It is also so the alternator on the engine can "help out" the 3000 watt inverter if I am using it on a heavy load.   Got a 60 or 70 amp circuit breaker on it (can't remember). Never tripped.  Other then that, no tests on it.

Here is one thing that surprised me though.  Here is a photo of the portable gas-driven battery charger I built.  6 horse engine was first coupled to a GM 140 amp alternator. Has 15 feet of #2 copper cables with 400 amp rated alligator-clips at the end.  I built this with the sole purpose of charging a small solar battery bank when badly discharged and the sun was not shining for a long time.   I had some surprises.  

#1 - the 6 horse engine could not run the 140 amp alternator.  If the batteries were half-discharged, that alternator put so much load on the engine it would just stall.  So, back to the drawing board.  I then removed the CS144 alternator, and stuck on an older GM 12SI rated at 67 amps.   Now - hooked it again to a half-discharged bank of 8 Walmart batteries via the 15 feet of cables.   Now it worked - but just barely at first.  The engine almost did not have enough power to turn that alternator making 67 amps.  Once the batteries got a little charge in them, it tapered to 40 amps and then there was plenty of power.

#2 surprise.  Once it ran for an hour, the batteries came up to 13.6 volts and stopped rising.  I was perplexed.  I checked voltage at the output of the alternator and it was 14.2 volts.   So there was a full 1/2  volt drop from one end to the other of those cables and that when only charging at 40 amps.  Math says the drop should only be 1.4% or  from 14.2 volts down to 14 volts.  I don't know how to account for that extra loss. The cable is very flexible welding cable and not the stiffer battery cable.  I do not know if that makes the difference.  So to fix the situation, I had to run a third small wire for 15 feet for "battery voltage sensing."  The Delco alternator has that option.  So now the alternator was sensing voltage AT the battery bank.  I then ran it and voltage at the bank eventually climbed to 14.2 volts and voltage at the alternator was almost 15 volts.   Point of this story is - there was a lot more voltage-drop then I predicted with math.  

Besides the portable charger - here are some photos of the #2 cable in my Minicruiser.  About 15 feet of run with a resetable 60 amp breaker on each end.

DSCF6760.JPG

DSCF2509.JPG

DSCF2513.JPG

Link to comment
Share on other sites

On 9/12/2016 at 11:06 AM, BobBeery said:

The question is why did it blow?  What would have caused it? 


So did all of this answer your question?  You surely got more than you asked for on this one.  I'm a two fuse kind of guy.  That is to say if a fuse blows, I change it.  If that goes, that equals two.  Only then do I start looking for why and what caused it.

My guess, there was an overly discharged house battery and upon starting the engine the alternator took out the fuse.  That is unless someone was working on the house side DC and shorted something, such as in taking out the house battery and running the truck engine and the line shorted out. All of this was speculation and guess work, all proving nothing with regard to your question.

 

 

Link to comment
Share on other sites

I suspect if someone has a fuse problem and it is OEM wiring - perhaps the wrong fuse is being used.   Note that if it is a typical fuse that measures 1/4" X 1 1/4" long - there are many different replacements.   A fuse in a charge circuit ought to be time-delay.   In this case with the size I mentioned - with Buss/Cooper brand - time-delay is type MDL or MDA.   "Fast blow" is type AGC.  "Very fast blow" is type GBB.   They all fit but are quite different.
 

Link to comment
Share on other sites

To clarify the original question, two points.  First, the isolator appears very new, like either this summer or at most last summer.  The wire from the engine battery to the isolator is black at the battery, spliced to nice clean red less than a foot from the isolator.  The red part had the 30A fuse in it.  Fuse was about one-half inch square.  So based on appearances I would say that this is NOT original Winnebago wiring.

Second, I don't know when the fuse blew.  When I test drove the Warrior before buying it, the battery under the hood was dead.  We had to jump it to start the engine.  And days later when I paid for it and drove it home, the house battery was too dead to get any ceiling lights to turn on.  Both these dead batteries suggest that the alternator would be at high output upon starting the engine.

I have been very busy but did manage to mount a self-resetting 30A circuit breaker right next to the isolator.  I am hoping to put the wires on it today and expect the problem to be fixed.

Link to comment
Share on other sites

A voltmeter is your best friend at this point. Start at the alternator and work your way back to each battery. Check at each point you can get a probe to. I THINK some where in the charging circuit Toyota uses a fuseable link.

Link to comment
Share on other sites

16 hours ago, BobBeery said:

To clarify the original question, two points.  First, the isolator appears very new, like either this summer or at most last summer.  The wire from the engine battery to the isolator is black at the battery, spliced to nice clean red less than a foot from the isolator.  The red part had the 30A fuse in it.  Fuse was about one-half inch square.  So based on appearances I would say that this is NOT original Winnebago wiring.

Second, I don't know when the fuse blew.  When I test drove the Warrior before buying it, the battery under the hood was dead.  We had to jump it to start the engine.  And days later when I paid for it and drove it home, the house battery was too dead to get any ceiling lights to turn on.  Both these dead batteries suggest that the alternator would be at high output upon starting the engine.

I have been very busy but did manage to mount a self-resetting 30A circuit breaker right next to the isolator.  I am hoping to put the wires on it today and expect the problem to be fixed.

The black wire from the "cranking" battery when wired by Toyota - was hooked to an 80 amp fuse.   Certainly not a 30 amp fuse.   Toyota used an 80 amp fuse with the 60 amp alternator, and a 60 amp fuse with the 55 amp alternator.   Again - not very confusing if someone stuck a 30 amp fuse in there and it blew.  Note that Toyota used slow-blow "fusible links" as main fuses,  The main fusible link hooked to a Toyota-Denso 60 amp alternator is a short piece of 14 gauge wire with fire-proof insulation that needs pretty steady 80 amps of current to blow.

What many if not most RV builders do is this.  They cut the output wire from the alternator.  Then splice new wire into it and then hook it to the middle post of the solid-state isolator (the "in" post). Then often the output the "house" battery has a fuse.  Usually NOT to main battery.

Your alternator via the regulator senses battery voltage and responds. If voltage is low enough in any of your batteries - it will try to send max output of 60 amps. It is as simple as that as far as the OEM system is involved.  The only catch is . . . due to the isolator that only permits current flow one direction - the alternator never gets to sense actual battery voltage and has to "guess."

I will note that in many older RV articles (from the 70s and 80s), it is warned that RVs with added isolators should not be revved up when first started or the added fuses can blow.  

Now - about your specific vehicle.  I cannot tell if the alternator is still protected by the 80 amp fuse that Toyota put in there.  It depends if the main output wire from the alternator was cut before it gets there and re-routed. If it WAS cut - this is what you should have.  The main output wire from the alternator should run through a 80 amp fuse, and then to the isolator.  Then - from the post on the isolator that does to your main "cranking" battery, no fuse is needed as long as that wire is 8 or 10 gauge.   The post on the isolator that does to your "house" battery is a different story.  If your "house" battery is in back somewhere and the wire is only 10 gauge - then it ought to be protected by a 30 amp slow-blow fuse, fusible-link, or circuit breaker.

 

Image2.jpg

Link to comment
Share on other sites

Today I connected the wires to the 30A self-resetting circuit breaker and am pleased to report SUCESS.

For convenience I checked voltages at the connectors on the converter's 12V circuit board.  With no shore power and engine off I read 12.56V for the house battery.  After starting the engine and while it was still on fast idle the voltage at the same connectors read 13.46V.  Upon shutting off the engine the reading went to 12.88V dropping to 12.87V while I still had the probes touching.  So--

It works.  Driving down the road will now charge the house battery, and that is really all I cared about.

Thanks to all who contributed to this thread.  I am done with it now but others may still post if you wish.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...