Would like some recommendations for a 270amp+ battery isolator

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Would like some recommendations for a 270amp+ battery isolator

May 23, 2016, 12:28:14 pm

Hello,

Back in March the alternator in our rig failed and you folks helped me diagnose the problem.

Engine start battery voltage drop. Where to get fixed in Tucson AZ? (solved)

In the 31st reply, John D. said to check the capacity of the battery isolator to make sure it can handle the capacity of the current alternator. The current alternator is a Leece-Neville 4874JB. It's a 270 amp alternator according to the following site:

Prestolite - Leece Neville

According to Foretravel, the original isolator is rated for 200 amps. So, to be safe, I need to replace it with a higher capacity unit. Any recommendations?

A brief search turned up this:

Sure Power 3002 Battery Isolator 300A 3 Studs

Thanks for any help - Joe

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #1 – May 23, 2016, 12:36:17 pm

Joe
That isolator is just what you need. Here is another source with slightly better price:

Surepower 300 amp isolator

I put one in last year when I upgraded my alternator to 300 amps. Mine is a 1 input, 3 battery version. I paralleled 2 legs together for higher house current capability to handle a larger inverter I also recently installed.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #2 – May 23, 2016, 12:48:43 pm

Sterling makes a smart 250 amp rated zero voltage drop isolator that will connect to three battery banks if you have them (or two). Sterling products are very robust, 270 amps should be OK but ask.

On sale right now at Bay Marine Supply. ~$230. Alan is a FF member and will give you a discount as well. $8.95 shipping.

Sterling ProSplit-R – Zero Voltage Drop Battery Isolator

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #3 – May 23, 2016, 01:44:58 pm

This is my preferred solution, a 500A rated voltage sensitive relay:

ML-ACR Automatic Charging Relay - 12V DC 500A - Blue Sea Systems

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #4 – May 23, 2016, 01:50:12 pm

Blue Sea makes excellent products. I have purchased and fully recommend them, I used their panels, switches, dimmers and relays on my boat. Just hook house to one terminal and alt and start batteries to the other terminal. I use this setup on my boat, and have never had an issue.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #5 – May 23, 2016, 02:32:14 pm

Quote from: Tom Lang – May 23, 2016, 01:44:58 pm

This is my preferred solution, a 500A rated voltage sensitive relay:

ML-ACR Automatic Charging Relay - 12V DC 500A - Blue Sea Systems

Tom: That looks like an awesome unit, might have to order one!

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #6 – May 23, 2016, 02:53:34 pm

I have their SI-ACR, which is only rated at 120A continuous, 210A for five minutes. I am completely satisfied with it.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #7 – May 23, 2016, 05:24:51 pm

Now I have Isolator & Alternator Envy. I wish you guys would quite posting stuff that I have to add to my "Want But Don't Absolutely Need" list.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #8 – May 24, 2016, 10:18:54 am

Thanks for the input. Need to do some studying. To "Chuck and Jeannie", I kind of wish our rig had the stock alternator in it so I didn't need to make the change. We're new to using a motor home, but it seems that 200 amps is plenty.

Just out of curiosity, in a situation were you have been dry camping and are now on the road and the engine is charging the house batteries, what controls the voltage and amperage going to the house batteries, the alternator/voltage regulator or the inverter? I assume our rv wiring hasn't been changed from original.

Joe

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #9 – May 24, 2016, 11:10:28 am

When the engine is running and there is no other source of power (no ac power, no solar power) the engine alternator is charging everything. It's amps are split between both battery banks in proportion to need and, with cable length, resistance, and isolator voltage drop reducing amps somewhat. The alternator sees whatever voltage it is sensing and tries to maintain a constant charging voltage limited only by its amp limit and temperature.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #10 – May 24, 2016, 11:12:02 am

Quote from: joe g – May 24, 2016, 10:18:54 am

Just out of curiosity, in a situation were you have been dry camping and are now on the road and the engine is charging the house batteries, what controls the voltage and amperage going to the house batteries, the alternator/voltage regulator or the inverter?

Tom beat me to it. Here is my more long-winded answer.

Good question. First, take the inverter completely out of this discussion. The inverter takes 12 volt DC power from your batteries, and changes it to 115 volt AC. Inverter has nothing to do with charging (when driving down the road)(with generator off).

In our coaches, with the typical OEM diode based battery isolator in place, the voltage put out by the alternator is controlled by the internal voltage regulator. Say it is putting out 14 volts. That output goes to the center post on the isolator. The isolator is basically 2 one-way check valves. It routes the voltage from the center post to the 2 (or more) battery posts. There is some voltage lost going through the diode "check valves". This is usually around 0.7 volts. So with 14 volts input at the isolator, the batteries in both battery banks will see about 13.3 volts. This is not enough to fully charge the batteries, so we must "trick" the alternator into putting out more charging voltage. This is accomplished by the "SENSE" wire, which is connected to either the "Start" battery post on the isolator, or directly to a positive (+) post on one of the the start batteries. The alternator increases charging output until the voltage read by the sense wire makes it happy. In this example, it would increase output to 14.7 volts, which would result in the start batteries (and house batteries) seeing a charging voltage of 14.0 volts.

Charging amperage is a function of the state of charge of the battery. Amperage is higher when the battery is deeply discharged. As the charge level of the battery increases, the amperage it will accept decreases.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #11 – May 24, 2016, 11:48:03 am

Quote from: joe g – May 24, 2016, 10:18:54 am

Thanks for the input. Need to do some studying. To "Chuck and Jeannie", I kind of wish our rig had the stock alternator in it so I didn't need to make the change. We're new to using a motor home, but it seems that 200 amps is plenty.
Joe

Joe:
To paraphrase an old saying - "there is no substitute for alternator amps"

In my case, I added additional 12V loads, and run the refer on the inverter when driving. So instead of running near the stock alternator limit, a larger one runs easier and cooler.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #12 – May 24, 2016, 12:25:09 pm

Joe
After boondocking, on the morning I was going to travel, I would start the generator when I got up. I would turn the boost sw on and let the generator handle the 120v needs of the morning and let the battery charger put a lot of amps back into both battery banks before engine start.
If I can, I like to use the alternator to replace what it took to start the engine and a little more. I don't like to use the alternator to recharge grossly discharged batteries, and in a coach with a generator and battery charger like we have in these coaches there is no need to. The generator can stand a little exercise after a few days off anyway.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #13 – May 25, 2016, 12:03:30 am

Thanks folks for the education. I was using the term "inverter" a bit loosely. It is my under standing that the "inverters" have the ability to both change DC to AC and charge the house batteries when an AC source is present. Is "inverter/converter" more accurate or is there a separate battery charger? I was mainly wondering if the output from the alternator made it's way through the "inverter/converter" or a separate battery charger and was tweaked so as to be at an optimal voltage for the batteries before reaching the house batteries. It was my impression that the "inverter/converter" is really good at charging and maintaining a battery, and was curious if it was used when the engine is running. Sounds like it's not.

This brings up another question. What is charging the house batteries and the start batteries when the engine and the generator are both running? What about when the engine is running and you are plugged into shore power? Sorry if this info is in the documentation, I admit I haven't read it all yet. Even though we're full timers, I'm travelling away from the motor home right now and don't have access to the files, and my curiosity is getting the best of me.

Regarding the isolators, at first blush I'm leaning towards the Sterling product. Zero voltage drop, less heat, and cheaper than the Sure Power diode based isolator. It sounds a bit too good to be true. What's the downside of going with a non-diode type isolator? Is one type more reliable than another?

John, I agree with you. It makes sense to use the generator to charge the house batteries after boondocking since it was designed and built to do that. By doing that, my alternator will probably never put out over 200 amps for a long period of time and the isolator would be fine. But, thanks to you, I know that my isolator is under capacity and will take the safe route and get a bigger one.

Joe

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #14 – May 25, 2016, 12:38:59 am

Joe,

No problem with asking any question around here. You will often get a wide spectrum of answers - just pick the one you like!

Terminology:

Our old '93 GV was originally equipped with a stand-alone inverter, and a separate converter/charger. The inverter had only one job: change 12 volt DC from the house batteries to 110 volt AC. The converter/charger had two jobs: when it was supplied with 110 volt AC input, it would provide a clean 12 volt DC output to run 12 volt devices, PLUS it would charge the house batteries.

Later, we upgraded to a combination inverter/charger. This device does the inverting job when we are running on the house batteries, and also does the converting/battery charging job when it is supplied with 110 volt AC. It switches automatically between modes.

Since you have a newer model coach, it is probably equipped with a combination inverter/charger. Most modern inverter/chargers include a "smart" battery charger with 3 or 4 charging routines. If properly programed for your battery (bank) type and size, a "smart" charger will do the best possible job of maintaining the batteries.

When you have multiple charging sources running at the same time, the way I understand it is they all contribute charging amps to the batteries. Our coach has solar panels, in addition to the inverter/charger, and of course it also has a alternator. If we are driving down the road, in the daytime, with our generator running, there are three sources of charging amps being sent to the batteries. The alternator is charging both battery banks through the isolator. The inverter/charger is being supplied 110 volt AC from the generator, so the built-in battery charger is charging the house battery bank. AND, our solar panels are putting out charging amps, through the solar controllers, straight into the house batteries.

Note that (in most standard OEM setups) the alternator is the only charging device that automatically charges the "start" batteries. For extended periods of time when the coach is not being driven (off-season storage, long-term dry camping, etc) you must make other arrangements to keep the "start" batteries topped off. There are many ways to do this - search the Forum for recommended add-on aux battery chargers.

The batteries don't care where the charging amps originate. They will only accept as much power as necessary to reach full charge. All three charging sources will automatically taper off their output as the batteries reach full charge. The inverter/charger and the solar controllers will go into "Float" mode, where they put out little or no amps, depending on their program. The alternator will drop to its lowest output level, as directed by the internal voltage regulator.

This is my understanding of the charging system. If I am off base in any respect, rest assured another (more knowledgeable) Forum member will jump in and correct me. And I won't mind a bit, because I am always learning!

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #15 – May 25, 2016, 08:39:28 am

Quote from: joe g – May 25, 2016, 12:03:30 am

Regarding the isolators, at first blush I'm leaning towards the Sterling product. Zero voltage drop, less heat, and cheaper than the Sure Power diode based isolator. It sounds a bit too good to be true. What's the downside of going with a non-diode type isolator? Is one type more reliable than another?

Joe

Joe:

You will find as many isolator opinions as there are forum members.

The Sterling and Blue Sea isolators both have smart electronics involved, but are more efficient (less wasted power). The diode based isolator has no smart electronics, is bullet-proof reliable, but adds a small voltage loss. As has been mentioned, the alternator sense wire allows the alternator to increase voltage to account for any voltage loss between alternator and batteries (isolator voltage loss and any losses in your cabling). My preference was the simplicity and reliability of a diode isolator. I know other members are looking at the Sterling product, and there should be updates on how it works soon.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #16 – May 25, 2016, 09:38:23 am

I have the Sterling ProSplitR 250 amp 3 battery bank isolator. I knew I was going to get a bigger alternator at some point and add a third set of batteries (two) that have their own inverter just for the residential refrigerator.

The price was right. Alan is very helpful and knowledgable and want to make sure you get it right. It is waterproof so no issues there. Installation was very easy, fits right where the old isolator was and uses the existing wires. You do need to add one wire to let the Sterling know that the ignition is on. It is an easy addition. I added a jumper between banks two and three until the third bank is actually installed.

The Sterling is doing exactly what it is supposed to do. It has a panel of diagnostic lights so that you know what it is doing. All of my batteries are getting charged. It was a good choice for me.

You may need to adjust the voltage output on your LN alternator. When using a diode based isolator the output voltage is increased by 1/2 - 1 volt to account for the voltage loss accross the diodes. As I recall with the Sterling I adjusted mine down to 13.8 - 14 volts. I think it was closer to 15.

Any of the choices mentioned will do the job.

If you are going from a 160 amp alternator to a 270 amp alternator you probably should go to a 3/0 wire from the alternator to the isolator and from the alternator to ground. The original on mine was 2/0 which was undersized at maximum output which doesn't happen often. That may be what is already on your Nimbus.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #17 – May 26, 2016, 08:55:21 am

My house batteries were not charging all the time. Was told to replace the isolator. Had a 300 amp so replaced with same. All now works like it supposed to. .

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #18 – May 26, 2016, 10:38:31 am

Thanks for the comments. Very helpful. Roger & Susan, I didn't know you could adjust the output voltage on an alternator, I thought the internal voltage regulator did that. How did you do that?

Also, regarding the wire size, hopefully, who ever put in the larger alternator did that, but I'll double check.

Joe

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #19 – May 26, 2016, 11:20:54 am

Joe,

Many LN have an adjustable voltage output. You have to figure out if your specific one does.

See Alternator Troubleshooting Flowchart

Leece-Neville alternators are equipped with one of two regulators. The Fully Adjustable Regulator has a flat cover plate. The Three Step Regulator has a finned, curved cover plate. Use the following test procedure that is appropriate for you regulator type.

From LN

Fully Adjustable Regulator

NOTE: Battery must be at least 95% charged prior to this procedure. Also make sure wire connections and belt tension are OK.
1. Shut off all electrical accessories and run the engine at approximately 1000 RPM.
2. Connect a voltmeter to the alternator outputs.
3. Remove the plastic screw from the regulator (see photo) and insert a small screwdriver in the hole. Engage the screwdriver blade in the slotted adjustment screw inside the regulator.

CAUTION: The adjustment potentiometer screw has high and low stops. DO NOT exert excessive pressure on the screwdriver or you may damage the regulator.

Voltage Regulator Adjustment
4. Turn the screwdriver clockwise to raise the voltage, counterclockwise to lower the voltage. Set the voltage between 14.0 and 14.2 volts (28.0 to 28.4 volts for 24-volt units).

CAUTION: DO NOT force the screwdriver past the set stops at either end of the adjustment range to avoid regulator damage.
5. Remove the screwdriver and voltmeter and install the plastic screw in the adjustment screw access hole.

On your FT adjust the voltage at the start battery to be 14-14.2 volts. This adjusts for any voltage loss through the isolator. The voltage at the alternator will be a little higher.

There are others out there that know more than I do about this. This is what I did. I hope they add to this. Great way to learn. And of course your coach is likely different from mine.

Re: Would like some recommendations for a 270amp+ battery isolator

Reply #20 – June 09, 2016, 03:06:17 pm

At Roger and Susan. Thanks for that info. I haven't decided on the new isolator yet. Been distracted. I'll post what I end up with.

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