[kaptain]

While I was about to install the newly arrived Xantrex Echo Charge onto my 701, I further checked the wirings. I discovered a new issue: the battery isolator is apparently defective and needs replacement. The defect is that a middle (input) stud is broken or missing, and four (4) thick red wires are connected to one single stud.

This connection seems to purposely bypass the battery isolator to establish connectivity allowing electrical current to flow, but in any direction now, instead of limiting one-way-only flow from the alternator to the two battery groups.

See the attached photos showing the wiring issue. Now I believe the erroneous wiring here (might be as well as the erroneous wiring with Xantrex charge) are intentional rather than a mistake.  And I wonder if this was done by any repair shops or the previous owner. 

   
   

And I created a schematic that hopefully better illustrates the issue: three battery isolator terminals: A (output), B (input), C (output). Now connects A,B,C together - that's the issue.

   

So I started looking to buy a new part to replace the Sure Power 3002 on my 701. This is a battery isolator rated at 300 Amp. "Sure Power 3002" seems a discontinued/obsolete product for some time already, and it is hard to find. A few listings I could find show price over $500, even with used ones.  I found a Sure Power 3003 (which supports three battery groups) that also costs cover $500. 

So I started thinking about my options. Do I really have to buy the same model or the same type of battery isolator?  My understanding is that the Sure Power 3002 basically consists 2 large capacity diodes with a big heatsink. I could buy 2 or 3 large capacity rectifier diodes (prices around $10-$20/each) and build an isolator for under $100, but using rectifier diodes for current directional flow has one major drawback: a 0.65-0.75 voltage drop or power loss.   

My second option seems to go with mechanical relays. Many such relays are sold on Amazon, listed as Smart Relay Isolators, which switch on when the alternator has an output (engine running). When the alternator has no output (engine off), the circuity is automatically cut off, thereby disconnecting and separating batteries. The advantage of such a mechanical-based isolator is that there is no voltage drop like diode-based ones. But these types of relays rely on mechanical contacts to open/close; over time, these contacts go bad, especially switching on/off at an electrical current. 
Here are several mechanical relays seem attractive:

https://www.amazon.com/dp/B084VVGT4T/
https://www.amazon.com/dp/B09Q27WCHM/
https://www.amazon.com/dp/B08SW4XVNR/
https://www.amazon.com/dp/B004WDPZEW/


My 3rd option seems to use a "Schottky Diodes" based isolator, which works the same principle as the SurePower 3002, but it improves the voltage drop by half or ~0.3v (low current) to ~0.45V at high current.

So I kept thinking and searching. I see there is another type of isolator that employs MOS-FET. This type of transistor works great as a solid-state open/close switch over high currency, the advantage is it can reach near-zero voltage drop. Examples of such are made by Analytic Systems, Model: IBI1-40-340 cost about $200, this is attractive.

After considering several alternatives for replacement, I decided to go with "Victron Energy Argo FET Battery Isolator, 200A", which supports 3 batteries, although I only need support for 2.
https://www.amazon.com/gp/product/B00UAN0HBE/

FET isolators allow simultaneous charging of two or more batteries from one source without the voltage loss associated with common diode isolators. I see Victron makes both (Schottky) diode-based and FET-based.

   

Now, here are my questions and a few items I need help on:

1) What is the isolator on your coach, maker, and model? I'd like to see how Newell fast changes and moves from older/traditional isolators to new ones over the years.

2) What would be your choice if you were me?

3) What type of alternator is on your coach? I have a Delco Remy 50DN, Part# 1117860. My alternator is good, but I'd like to read its wiring information.
    I found some documents online about this type of 50DN alternator, but none of such documents contained wiring information.
    https://www.delcoremy.com/support/servic...ion-sheets

4) I measured my house battery negative terminal against chassis metal. It reads about 1 volt. I thought the chassis metal should be ground therefore 0 voltage from the battery was negative against the chassis metal. What's the reading with your coach, with Alternator/Charger cut off both on and off?

[Richard]

Joe,

I am a bit confused. When you were talking about the Echo charger issue, you measured distinct differences between your house and chassis batteries. If both banks are tied together at the isolator in your picture, I don’t see how a difference in voltage is possible. I must be missing something.

[kaptain]

Joe,

I am a bit confused. When you were talking about the Echo charger issue, you measured distinct differences between your house and chassis batteries. If both banks are tied together at the isolator in your picture, I don’t see how a difference in voltage is possible. I must be missing something.

 
Excellent point! However, the voltages of the house and chassis can only converge to the same reading when both disconnect switches are left closed (ON position), regardless the Xantrex charger is running or not.
I have to keep the chassis battery cut-off switch OFF position while the coach is sitting to prevent battery drain.

The steps of my previous measurements were taken in these steps, but now I see flawed:

1) shore power off, house switch off, house battery at 12.96; 
2) shore power still off, chassis switch OFF, chassis batteries 13.0
3) shore power on, thus Xantrex charger on, house battery rises to 14.15v
4) now turn the chassis power switch on. The chassis battery drops to 12.89 (from 12.96);

At this moment, I should have gone back to re-read the house voltage.



If my drawing is correct, the house-B and chassis-B voltages should be converging now (note: All steps were taken without attempting to crank or run the engine)
I can re-check and see if its house-B voltage is dropping quickly right at step (4)
Theoretically, when both shut-off switches are closed, without loads and parasitic leaks,  the house-B voltage goes down, and chassis-B goes up. 

If I have heavy loads somewhere, both battery voltages want to go down, but with the Xantrex charger running, it may not go down too much.
How low it can go is probably determined by the Xantrex FSW-3012 capacity. Marc Newman replaced at least once the charger, the generator, and the engine starter as well because the starter clearly shows the manufacture date:  2015-09. And Marc has had Newell replace his transfer switch eight times, which may or may not be related.

I don't know when these four (4) thick red wires were all connected to the single stud of the broken SurePower 3002 isolator. 

I believe if both shut-off switches are left at the ON position long enough, the voltage of all batteries will read the same. I remember this was the exact case 3 months ago when I attempted to pick up and drive home the 701 when the shop said repair works had been completed and ready for pickup, both battery groups at 4 volts: http://newellgurus.com/showthread.php?ti...8#pid55288
Since then, I have replaced with good batteries.



I will re-check and provide an update.

[bestgenman]

While you are considering products, maybe another less corrosive and vulnerable location would be in order.

Cole Herese and Sure Power are two manufacturers that come to mind, SP2002 (200 amp) sells for $112.00 from my vendor.  Freight is so high now, it would probably cost $30 to ship!  Many other exotic components available, as you’ve mentioned.

You should be able to overcome the diode drop by increasing the 50DN output by whatever you desire.

My .02 worth!

[jumpshowhigh]

There's another product I've seen on my buddy's Marathon coach called Perfect Switch. It's better than regular or Schotky diodes, and it there's no heat sink....and he's running darn near 400 amps through it. When my blue brick isolator goes sideways, I'm seriously considering changing to to their two-in-one-out isolator. I looked at their website and it looks slick. Not cheap though.

[SouthernDevGirl]

@kaptain / Joe - That's a great schematic/photos.

I've probably read this too quickly or misunderstood something; however, what would be the reason not to simply go with a VSR (Voltage Sensitive Relay/Solenoid).

In other words, the alternator is direct-wired to the chassis-batteries; no Isolator/extra diode inbetween. Then, upon voltage reaching a suitable level, the solenoid connects the house batteries.

The level is typically one that must exceed a 12v battery output (eg 13.8v), indicating the alternator is effectively outputting current without substantial drain. As long as the alternator is running, the higher voltage automatically directs it to where it's most needed; you don't have an issue where an isolator is required in that situation because the alternator is always the highest-voltage source.

If you had different chemistries (eg LiFePO4 for the house batteries), this wouldn't be ideal; you'd be better off isolating with a DC-to-DC charger to gain some additional intelligence/logic; however, with SLA/AGM on both sides, I don't understand the benefit to a traditional isolator over the easier/less-expensive voltage-sensing switch.

I suspect I'm missing something obvious, but I felt it couldn't hurt mentioning on the off chance it inspired any new approaches

[kaptain]

@kaptain / Joe - That's a great schematic/photos.

I've probably read this too quickly or misunderstood something; however, what would be the reason not to simply go with a VSR (Voltage Sensitive Relay/Solenoid).

In other words, the alternator is direct-wired to the chassis-batteries; no Isolator/extra diode inbetween.  Then, upon voltage reaching a suitable level, the solenoid connects the house batteries.

The level is typically one that must exceed a 12v battery output (eg 13.8v), indicating the alternator is effectively outputting current without substantial drain.  As long as the alternator is running, the higher voltage automatically directs it to where it's most needed; you don't have an issue where an isolator is required in that situation because the alternator is always the highest-voltage source.

If you had different chemistries (eg LiFePO4 for the house batteries), this wouldn't be ideal; you'd be better off isolating with a DC-to-DC charger to gain some additional intelligence/logic; however, with SLA/AGM on both sides, I don't understand the benefit to a traditional isolator over the easier/less-expensive voltage-sensing switch.

I suspect I'm missing something obvious, but I felt it couldn't hurt mentioning on the off chance it inspired any new approaches

Using a Voltage Sensitive Relay/Solenoid (VSR/VSS) might be a good option, provided the on/off triggering voltage is significantly different. Why? I see a potential problem using such electrical-driven mechanical here. The sudden click-on/click-off of the charging circuit can create a significant electric flow between 2 battery groups, it may not behave well on a traveling coach. 

Let's say the trigger voltage is 13.5 to turn on the circuitry to charge house-Batt. We have the engine on, the alternator working, and the coach is traveling. 
In the beginning, the voltage of the Chassis-Batt could be around 12v right after cranking the engine; at the moment, the Alternator only charges the Chassis-Batt, because trigger voltage has not yet reached.
Let's say the voltage has just reached 13.50v, the triggering voltage. VSR clicks on, and the House-Batt voltage immediately starts to rise from 12.0v
The sudden switch-on of the VSR (effectively merge) can be a big load on the alternator and the Chassis-B, which, therefore, causes the voltage of the chassis-Batt drops quickly (it wants to get equal to the voltage of the House), now the alternator also has a higher load because more batteries to bring up voltage. Let's say Chassis-Batt quickly dropped below $13.50, thus causing VSR cut off the changing House-Batt. Chassis-Batt voltage rises again above 13.5v, and the cycle repeats. Now the VSR is acting like a flip-flop circuitry while charging both battery groups until both voltages of both battery groups have converged and stabilized above 13.5v, now the VSR stays closed, allowing both batt groups to charge.

Then you might have other devices that affect the voltage of the traveling coach, let’s say you just started to cook dinner, inverter comes on, drawing electricity from both battery groups until voltage goes below tigger 13.5, VSR opens….
I see it won’t be stable using a VSR, the original design concept ALWAYS separating 2 battery groups should be kept. We still have the option to use the merge switch.

[SouthernDevGirl]

Joe,
Based on your hypothetical/concerns, I'm certain there will be no issue.

(1) For starters -- A good quality marine/RV VSR won't have the flip/flop issue you mention because it will require a _sustained_ period of voltage to make a switch. They also have a low-voltage cutoff, meaning that you'll never have a parasitic drain when one bank suffers a terminal flaw and won't reach nominal voltage.

(2) You'll never drain your chassis-batteries into your house-batteries, or overload your alternator (providing both sets of batteries are SLA/AGM -- if they aren't, there's an alternative solution).

(2)(A) The idea of overloading a quality alternator intended for low-RPM diesel engines is difficult to start with, because they don't suffer the same issue with conventional automobile alternators overheating when running a lower RPM (less cooling).

(2)(B) When you consider that you're dealing with the IRR of SLA/AGM batteries, the issue is further mitigated, even with the large 6x 8D battery bank.

(2)© The output current of the alternator is truly pushing the limit of the wiring and the current the house batteries can accept. Therefore, it's essentially impossible for the VSR to be "on"/connected more than the standard timeout period (typically 2 minutes or less) with the house batteries drawing from the chassis batteries. There are a couple reasons:

(2)©(i) The rate of resistance I mentioned above would indicate that if you were charging a completely dead (or just above the charge-cutoff) battery-bank, the circuit is: Alt > Chassis Bat > VSR (alternator flowing to chassis battery first at high amperage). If for any reason the house batteries could pull more current than the alternator made available, the voltage would have to fall closer to nominal, well under the VSR cutoff. In other words, 2 chassis batteries at 12.86 volts (a full+absorb voltage), with the house-batteries completely discharged at 11 volts (low IRR to accept the highest amperage). Alternator pumps past the high-IRR of the chassis batteries --into-- the house-batteries; no chassis-battery current can flow out. If it were to flow from the chassis battery, the voltage would be well-below the VSR cutoff.

(2)(D) Don't forget that many VSR's have manual override-switches; some are only to manually merge; however, some have a two-way override (merge or no-merge).

I really can't see a scenario where a VSR isn't better for your situation; none of the issues you're concerned with should be an issue with a quality VSR.

If something I explained doesn't make sense, I'm happy to get into more detail, just let me know!

[kaptain]

SouthernDevGirl, 

Thanks for sharing your thoughts. I'd agree with you it would work if the trigger-on and cut-off voltages are significantly different, then the flip/flop will not occur. 
As a matter of fact, before I decided to go with the Victron ArgoFET isolator, I had been seriously thinking about using this one
https://www.amazon.com/dp/B09Q27WCHM/ (Its the 2nd of the 4 I had listed above). 

It shows Trigger ON voltage at $13.3v, Cutting-OFF voltage at 12.8v, 
       


but I saw it it has a review showing it quickly failed at 120 amp.
https://www.amazon.com/gp/customer-revie...USBVTVJ98/

I think it is worth giving it a try if you could recommend something similar but of better quality, although I think it has another potential shortcoming is that being a coil/magnetic-driven mechanism, it consumes electricity itself in order to sustain electrical contact. I have seen such a relay consumes about 1-2 amps to keep closed.

[Richard]

If I could just weigh in with a tangent comment based on my experience. If the coach has the monster oil cooled alternator, this does not apply.

But if you have a Leece Neville or the Penn Tex alternator, even the ones rated at over 300 amps, charging a depleted house bank repeatedly with the alternator does lead to alternator failure. And to take that further, I have taken the isolator out of the circuit because I have lithium batteries. Perhaps my experience was unique, although years of following RV forums has numerous stories of alternator failure, so your mileage will vary.

If you use the coach pedestal to pedestal, and the only purpose of the isolator is to keep the house batteries topped off while traveling, I don’t think that puts much strain on the alternator. If you boondock, and draw the house batteries down, then depend upon the days drive to charge them back up, you may invite premature alternator failure.

So it brings up the point of why do almost all Class A manufacturers use some sort of isolator? I put that in the same category as the transfer switch that will switch power sources with all the AC units running. It’s one of those situations of just because you can, doesn’t mean you should.