Battery isolator

most post

will do

They comes and they goes on eBay. Gotta grabbem when they is...

Would you most make and model of them?

enblethen wrote:
I have not seen any large amperage solid state relays in a size that would work in RV battery centers or in an electrical area. I am thinking in the amperage range of 100 amps or greater.

Funny you should ask. I have seven 100-amp DC/DC relays coming down here from the USA next week. $15.65 ea on eBay + $1.25 China Post. The three that I have tested here do not current hog when in parallel. At >70% capacity they do need enhanced heat sinking. So a rectified alternator stator tap + fan are in their future.

DrewE wrote:
As I'm sure you probably realize, the isolator and the generator starting problems are not really related to each other, at least not directly.

Does the generator spin somewhat slowly when it does turn--does it seem to have a little trouble getting through the compression stroke? If so, I would guess that you have a problem with the generator's starter motor. On my generator, at least, the starter (a permanent magnet motor) had four poles, and hence four brushes, two positive and two ground. A failure in one of the brushes would and did result in it working, more or less, but marginally with approximately half the oomph it should have had. (It finally failed due to an attempted start on a cold winter day where it didn't have enough torque to pull through the compression stroke and, due to my pig-headedness in trying to hard, got a burned out coil or two. Replacing the starter was a pain, but the new one does work much more energetically and effectively and reliably.)

I was thinking the starter was bad at first… But then I started the coach engine and the generator spun up just like it should… Next time I started the coach engine, the generator was dragging a bit… So that led me to believe I might have some issues in the cleanliness of the cable ends... I looked at the isolator and The pole on one side of it ... the side going to the generator… The contact is rusted… so I thought I would start with the easy things first… Replace the solenoid and clean the Cable connection…

As I'm sure you probably realize, the isolator and the generator starting problems are not really related to each other, at least not directly.

Does the generator spin somewhat slowly when it does turn--does it seem to have a little trouble getting through the compression stroke? If so, I would guess that you have a problem with the generator's starter motor. On my generator, at least, the starter (a permanent magnet motor) had four poles, and hence four brushes, two positive and two ground. A failure in one of the brushes would and did result in it working, more or less, but marginally with approximately half the oomph it should have had. (It finally failed due to an attempted start on a cold winter day where it didn't have enough torque to pull through the compression stroke and, due to my pig-headedness in trying to hard, got a burned out coil or two. Replacing the starter was a pain, but the new one does work much more energetically and effectively and reliably.)

I have not seen any large amperage solid state relays in a size that would work in RV battery centers or in an electrical area. I am thinking in the amperage range of 100 amps or greater.

jumpshowhigh wrote:
This is not entirely accurate. Many RV manufacturers continue to use "diode" based isolator, but yes, they do have a significant voltage drop. The "diode" style isolators are being obsoleted by MOSFET-based isolators where the MOSFETS (semiconductors) behave just like large, high current diodes, but have an insignificant voltage drop my magnitudes of efficiency and some high end motor coach manufactures are migrating to this never (sic) technology. There are several companies that offer MOSFET based isolator, but the best I could find was Perfect Switch in California. No affiliation but a super-please customer, FWIW

Would you care to name a few, or even ONE?

Heh heh heh

Lettum try and produce a synchronous MOSFET switching system for an alternator stator and then I would be impressed.

High current mechanical relays have a number of issues but so do solid state relays. eBay has several vendors offering 100-ampere MOSFET DC relays.

Mechanical relays TEND TO fail in open circuit mode

Solid state relays TEND TO fail in shorted mode.

This is not entirely accurate. Many RV manufacturers continue to use "diode" based isolator, but yes, they do have a significant voltage drop. The "diode" style isolators are being obsoleted by MOSFET-based isolators where the MOSFETS (semiconductors) behave just like large, high current diodes, but have an insignificant voltage drop my magnitudes of efficiency and some high end motor coach manufactures are migrating to this never technology. There are several companies that offer MOSFET based isolator, but the best I could find was Perfect Switch in California. No affiliation but a super-please customer, FWIW

OnaQuest wrote:

KnowNuthin wrote:
Just recently the starting system on my generator began to act up… Sometimes it would spin just as it should… Other times I would just get a click and maybe a half a turn on the crank…

I've been investigating the electrical system and found that the solenoid type battery isolator in my coach typically doesn't last very long… A few years or so…I'm thinking the isolator that's in there now is the original from the manufacturer...

My question is… On the dash of my motorhome is an auxiliary start switch which I assume ties the two batteries together when activated to assistant starting the coach engine… Do I need a special isolator to keep this feature intact or will any three post battery isolator suffice...so long as the amperage rating is correct...

I'm planning on cleaning all the battery connections and running a separate ground to the generator from the coach frame… Hopefully that will keep the generator starter happy…

There are other reasons that you don't want the diode based isolator, (three post isolator)also. The main reason they are no longer used in large motorhome applications is the inherent voltage loss through the diodes. Your batteries may never receive a proper full charge.

I'd stick with the solenoid based isolator. JMHO

In many factory installations
Two functions are requested of the "boost" relay
In this application it needs to be a 100% Duty Cycle rated unit with proper current rating. The cheap ones die quickly get a good one. Be for warned the coil current of many of the higher current rated units have excessive as in 2amps or more coli current demands.

1 - The ignition key activates the "boost" relay which connects the alternator to the house battery bank enabling the engine to charge the house batteries

2- The dash mounted momentary contact "Boost" switch lets the house batteries help start the engine if the chassis battery is low