Battery Isolator Amperage

[Mean_Jeanne]

Aloha all:

The isolator in our Roadtrek has given out and I need to replace it. The manual says the alternator puts out 145 amps, but I have access to a new 130 amp isolator replacement. Does anyone have any thoughts about using that isolator in the system? I saw in another thread that someone had installed a Surepower 130023A (130 amp) and it didn't appear to be a problem!? Any input would be greatly appreciated.

Mahalo

Mike

[Monstermash74]

What year is your RT mine is a 00D190P it was installed with an Hehr-Powerline model #Dodge 22-16. The replacement I found on amazon was Victron Energy Argofet Battery Isolators 200-2AC

[blackbourn3704]

The alternator does not "put out" 145 amps all the time. That is the maximum rating it COULD supply if needed, like for example two bad batteries and all electrical loads turned on at the same time. I think you will be fine with a 130 amp rated isolator.

[pasusan]

How does one know when their isolator has gone bad?

Just wondering since our RT is a 2004 and we've never replaced it...

[phantomjock]

Mike -


blackbourn3704 has the right idea; an alternator provides what is demanded of it, at its designed speed. So if the batteries, and system "need" 200 Amps, but the alternator is only able to make 145 - Tough. Something won't run. (Without depleeting the battery bank!)

So what is the designed speed (RPM)? Alternators have a chart - you might be able to find one for your specific one. Else, here is a generic one, thanks to Physics Forum:




OK. So you'd get 145-ish about 4800 RPM - Alternator RPM - not the engine.

The ratio of the belt drive pulleys reduces the engine RPM speed required to create the alternator RPM for output in a "useful range." So if the pulleys were 2:1 You'd get 145 Amps - IF 'REQUIRED" - at about 2500 RPM engine speed. Or right around highway cruising speed, yes? But sitting in the park (at idle), more like 75 Amps. Keep in mind, as the alternator warms in the engine bay, and through charging, the output is greatly reduced. Could be 50% at max speed. Then that 145 Amp Alternator is only 70-ish Amps.

FWIW - the isolator in the mail is rated at 150 Amps. I would expect that is probably conservative, but wouldn't count on much more that 10-15 Amps over that. When/if you choose to upgrade to higher consumption requirements, there are other options to meet those too. And it is probably best to look at the entire system and tailor the components to the overall system requirements, Consumption, Capacity, Charging the Top3 in my mind.

Hope that is helpful.

pasusan: You could run a test. First I'd check the breaker and fuses attached to it. Then I'd want to use a Clamp-onAmmeter and put some loads on and check that way.


I'm sure there are other approaches. Best of Luck.

Cheers - Jim

[Mean_Jeanne]

BB, MM and P, thanks for the questions/
suggestions/solutions. Not much I can say that would even add to Jim’s thorough understanding/explanation…he’s been my go-to resource in this isolator replacement journey, so thanks again. ��������

Mahalo

Mike

[blackbourn3704]

Originally Posted by pasusan

How does one know when their isolator has gone bad?

Just wondering since our RT is a 2004 and we've never replaced it...

The isolator is not a consumable part like oil, tires etc. However it can fail which will cause battery problems. Our RT is a 1995 model and still has the original isolator. Sleep well tonight.

[Richard Cranium]

You're talking about the isolator FOR the coach battery? Do you have an invertor / charger? My RT has an invertor charger. I just turned off the charging part because I went LIPO and put in a dedicated charger for it... BUT If you do have an invertor / charger, what is it's amperage? That's what you have to size the isolator to. My Tripp Lite only would put out 55 amps max charging but recommends to set it for lower amps as it's better for the battery. The feed to it has a 70 amp fuse.
I'd say you're fine with the isolator you have even with a dead short as long as you have it fused right.

[pasusan]

Thank you phantomjock and blackbourn3704 for your replies. Looks like we can test it, but won't lose any sleep...

[Mean_Jeanne]

Originally Posted by Richard Cranium

You're talking about the isolator FOR the coach battery? Do you have an invertor / charger? My RT has an invertor charger. I just turned off the charging part because I went LIPO and put in a dedicated charger for it... BUT If you do have an invertor / charger, what is it's amperage? That's what you have to size the isolator to. My Tripp Lite only would put out 55 amps max charging but recommends to set it for lower amps as it's better for the battery. The feed to it has a 70 amp fuse.
I'd say you're fine with the isolator you have even with a dead short as long as you have it fused right.

Hello RC, thanks for the message. I'm replacing the isolator with the same make/model as the one that failed in MJ, so I'm hoping that it's covered.

M

[JohnnyFry]

That is my thought exactly. The isolator is basically a couple of diodes which ar, hopefully both rated at 130 amps. Typically the current through the isolator is divided between the coach battery and the engine battery and system. I never say my coach battery charge more than 60 amps, and that only for a short time but, of course, it depends on your battery configuration: a big AGM battery bank could draw a lot more. I have a digital ammeter on my alternator lead so I can monitor in real time while I am driving. I almost never see it exceed 100 amps (145 amp alternator) and that would only last about 4 or 5 minutes before it drops to 60 or 70 amps combined and I only see that if, for example, I am driving at night with the lights, radio and A/C running. Short story long: I wouldn't worry about it.

[JohnnyFry]

Another thing, as has pointed pointed out before, is that as the alternator gets hot its output goes down. When the unit gets hot, say 250-275ºF, the resistance of the stator windings goes up and the output goes down so, in any event, you are not going to get 145 amp output over the long haul.

[justducky]

Check the wiring diagram in your owners manual. My 2004 Roadtrek shows 50 amp thermal breakers installed at both ends of the 6WAG B+ battery cable sorunning from the isolator back to the battery so thats is the limiting factor on my van right now. Still using original powerline model 33-12 rated as 90 amps