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Topic: Bad Isolator? (Read 3276 times) previous topic - next topic

Re: Bad Isolator?

Reply #20 –
A few posts back Chuck asked why I replaced my original isolator. I had noticed after pulling in off the road it was hot to the touch. I know it's normal to produce some heat, but since I was going to replace my alternator I decided to put in a new isolator. The new isolator just feels warm now when I check it.

Here is the Sure Power 3 battery isolator for those that want to replicate the original parallel diode connection:

Sure Power 2403 Battery Isolator

This 240 amp unit will have 3 - 80 amp diodes, vs 2 - 120 amp diodes in the 2 battery unit. When high power diodes are paralleled, the current sharing will not be equal. When a diode heats up, the resistance decreases, as a result, one diode ends up taking on more current than the other diode, resulting in it heating up even more. As you can probably see this cycle will cause thermal run away, causing the diode taking the most current to eventually burn out if you give it enough current. This is why as a general practice, paralleling diodes is not recommended. This phenomenon can be mitigated if the diodes are heat-sinked together as they are in an isolator, and thermal runaway will probably not occur in our application, as high current conditions are short and infrequent. I don't want to cause concern to owners who have the 3 battery isolator setup - it will work just fine in our application.

Also, the thing to remember is the diode rating is the continuous current rating. The 120 amp diodes can probably handle 200 amps or more for short periods, which might occur for a short time when batteries are low, and this would exceed my alternator output anyway.

I considered the 3 battery isolator and decided one higher capacity 120 amp diode for each leg was optimal, and was a simpler setup without the extra jumper. Either approach will work fine, whichever one you feel will meet your needs.

Re: Bad Isolator?

Reply #21 –
Peter: I was gonna let this thread die, but since YOU kept it going I will add another note about my continued investigation into my isolator behavior.  I found a .pdf copy online of the "official" Hehr install sheet for Powerline isolators:

http://www.hehrintl.com/pdf/isoman.PDF

If you scroll down to page 5, you will find "test" instructions.  I did the "ohmmeter" test, and got exactly what they say is the correct result.  This would lead me to believe my isolator is OK.  However, the next paragraph is "test information for electrician".  The first step of that test says, "Engine not running: #1 terminal of isolator should read system battery voltage. #2 terminal should read auxiliary battery voltage. The "A" terminal should read 0 volts."  My isolator fails this step (I have not yet performed the "engine running" steps 2 and 3).  So this indicates (to me) that my isolator is malfunctioning.

At another website, I found reference to "stray voltage on the isolator alternator post".  They suggested grounding the ALT post to bleed off "residual voltage", then checking again with multi-meter.  So I tried that - I removed the alternator feed wire from ALT post, checked voltage on post: showed 13.9 volts.  I then ran a jumper wire from ALT post to ground.  There was no spark when I connected the wire.  Then removed ground wire and checked voltage on ALT post: again showed 13.9 volts.  I then tried connecting a 12 volt test light from Alt post to ground - the bulb remained off.  This would seem to indicate that although I have voltage on the ALT post, there is no "current" or virtually zero amps?  I tried the DC amp and milliamp position on my multimeter between ALT post and ground, and couldn't get any reading.

All seems kinda contradictory to me.  I will wait until I get a chance to check the test steps 2 and 3 with the engine running, before I finally decide if I need a new isolator.  Your points about "3-post" versus "4-post" seem logical, but so does Neal's basis for preferring the 4-post design.  Price factor would seem to favor the 3-post model (at least in the Sure Power line).

I really like these kind of discussions!  The more I read and listen to the excellent forum member input, the more I learn!

Re: Bad Isolator?

Reply #22 –

Chuck:

As Neal has posted earlier, using voltage or resistance measurements to trouble-shoot high power diodes is problematic because of small reverse-bias leakage current that is normal. What I would recommend is trouble-shooting your isolator by measuring current flow. I purchased this clip-on DC current meter and find it extremely useful:

Extech DC400 400A DC Mini Clamp Meter - Amazon.com

With this meter you can do the following isolator checks (and at the same time check your alternator):

With meter on low current setting, shut engine off, turn on headlights and some coach lights (create a current draw on house batteries and chassis battery)
- Current flow on wire to alternator should be negligible to zero.
- Current flow on wire to coach batteries should be negligible to zero.
- Current flow on wire to chassis battery should be negligible to zero.
- If there is any measurable current flow on any of the wires, you have an isolator problem.

With meter on high current setting, start engine, turn on headlights and some coach lights (create a current draw on house batteries and chassis battery)
- Measure current on alternator wire (there should be measurable current, say 40 amps...)
- Measure current on house battery wire (there should be measurable current, say 20 amps...)
- Measure current on chassis battery wire (there should be measurable current, say 20 amps...)
- House and chassis currents should equal alternator current
- If there is proper charging voltage on the alternator wire (14.5 - 15 volts) and current on either of the battery wires is unusually low or zero, you have an isolator problem

If all measurements check out, isolator is fine and alternator is charging.

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Bad Isolator?

Reply #23 –
A voltmeter will also give you a good indication of isolator health.

Check the battery voltages with minimal loads and no charging. With the engine running, both batteries will see an increased voltage. With the ac charger charging, the house batteries will see an increased voltage, but not the chassis batteries.

Re: Bad Isolator?

Reply #24 –
Peter: The Extech DC400 sounds like something that needs to be in my tool box.  I'll add it to my Amazon "Wish List".  Thanks for the Tool Tip!

Tom: I'll try your checks the next time I run the big engine, but I think the Trik-L-Start may negate the results, since it charges the start batteries anytime the coach batteries are being charged, regardless of charging source.

Re: Bad Isolator?

Reply #25 –
My approach to diode isolator and boost solenoid use is as "KISS" as it can get. I do not use them, and while they are still mounted in my coach, they are not connected.

I have one three 8D battery bank, which provides 12 volt power to coach circuits and to chassis circuits. These  three 8D batteries are deep cycle batteries which will provide more cold cranking amps than the three Red Top start batteries Foretravel installed to power the chassis circuits. For this to be successful, you must carefully manage the state of charge of your batteries. I keep my batteries charged with solar panels, and have installed an amphour meter on each battery.

If you use solar panels and your batteries are fully charged each day, give my approach a try, it works very well for me.








Re: Bad Isolator?

Reply #26 –
Quote from: P. Wyatt Sabourin –
My approach to diode isolator and boost solenoid use is as "KISS" as it can get. I do not use them, and while they are still mounted in my coach, they are not connected.

I have one three 8D battery bank, which provides 12 volt power to coach circuits and to chassis circuits. These  three 8D batteries are deep cycle batteries which will provide more cold cranking amps than the three Red Top start batteries Foretravel installed to power the chassis circuits. For this to be successful, you must carefully manage the state of charge of your batteries. I keep my batteries charged with solar panels, and have installed an amphour meter on each battery.

If you use solar panels and your batteries are fully charged each day, give my approach a try, it works very well for me.











And if a worst case sceneario hits, all batteries too dead to start the generator and the sun down, you still have the Suzuki and a set of jumper cables.

Re: Bad Isolator?

Reply #27 –
What would happen if I connect a "Red" positive cable from Alternator connection post on the Battery Isolator directly on to Engine Battery "Positive" terminal while keeping everything in original "OEM" set up?

I read through 3 post vs 4 post Isolator discussions (Thank you for great information!) perhaps it went over my head a bit ... I was thinking to replace my 20 year old 4 post Battery Isolator with a 3 post. Currently I have all new 4x6v Golf Cart battery set up for my house batteries and once they are charged over night they have almost 500amph. More than good enough to run the residential Fridge and a floor fan all day (that's how i travel to west cost last year. Once i was in CO there was no need for Gen to run the over head AC. So essentially I have two batteries one for Engine & "one" for House, what would be the advantage of having a 4 post Isolator. I am thinking 3 post is all it needs no?

My problem is there is a .60v drop to engine battery. I discovered it by using a voltmeter on the Isolator. While Engine running, in idling mode (i was alone & could not get some one to rev it up to 2k rpm) on Isolator ALT post reads 12.40~12.60 (i know my Alternator is suspect too) House Batter Post & House Battery readings are same, same as ALT post reading. So that side is healthy. But the Eng Battery post side is 11.70~11.90 never 12v. It does go up to 12v when booster switch is turned on.

Has anyone done Brett Wolf's "KISS" method, if so what brand/ kind of switch would i use? 
I rather charge my Engine battery when driving and leave the house battery charging to shore and Generator power. But I will still like to keep booster capability in place.

Thank you for your help!
AL

Re: Bad Isolator?

Reply #28 –
Al,

Be aware that it is NORMAL to have .6-.7 VDC drop across the battery isolator.  SO, alternator should put out 14.7-15.0 VDC (measure at B+ terminal of alternator or center lug of isolator.

The two outer lugs (to the battery banks should each read around 14 VDC (that .6-.7 VDC lower than the center lug).

Now, if one outer lug reads substantially lower, then the other, THAT is a problem (assuming that battery bank is good and not deeply discharged).

Re: Bad Isolator?

Reply #29 –
Good day,
Thinking I would like some advice to the following question. Looking at the attached picture can anyone advise by looking at the isolator which side is going to the start batteries and which side is going to the house batteries. The isolator does not have any labeling. I am installing a new cole hersee 200 amp continuous isolator as well a new cole hersee 200 amp solenoid.  ALSO do these cables look ok or would I be better advised to replace the orange cables shown
My coach is stored for the winter so I can not crawl in to check the connections...

Re: Bad Isolator?

Reply #30 –
Doesn't matter on the house and start whwhich outside terminal they go on. The center cbl is from the alternator. The cable definitely need a good cleaning, aside from that no way other than a voltage drop test under a load.

Re: Bad Isolator?

Reply #31 –
Compare the little white labels on the cables to your schematic and you can quickly see which goes to which bank. Your cable lugs probably just need cleaning. The isolator panel is in a terrible location so frequently needs attention so everything is trouble free. Take a phone photo before taking anything off so it goes back on correctly. The previous owner of ours had mixed everything up.

Lots of ways to clean up cable lugs. I've even used a hand held HF sandblaster with sand, beads or shells.

Pierce

Re: Bad Isolator?

Reply #32 –
Other way to identify "which is which" is with a digital voltmeter.  Very unlikely unless you have a battery combiner ON or boost switch ON for voltage to be exactly the same at each battery bank.  Compare readings at the lugs with that at the batteries themselves.

Re: Bad Isolator?

Reply #33 –
I keep a small roll of emery cloth to polish cable ends.  You can also use colored ty-raps to mark each cable & it's connection.  After cleaning and re-connecting put a coating of dielectric grease.