Replacing a burned-out automatic battery isolator

[BelleSerene]

I have a dual battery isolator between my battery banks, and it's been leaking sticky brown gunge. Clearly I need to replace it; my question is with what, and whether I need to replace anything else.

It's a PowerFirst PF702-4 (I reckon that's 70A-rated) battery isolator, fed by an 80A (!) alternator, an obsolete predecessor (ref 36 16257 12) of these [http://www.scheiber.com/doc_techniq...-batteries-de-moyenne-puissance-12v/?lang=en] by Scheiber, and a MasterVolt Alpha Pro charge regulator. The domestic battery bank is 2 x Rolls 230Ah AGM, and the engine battery is a 115Ah deep cycle.

I just found that some of the terminals on that Scheiber box had been disconnected by a yard that had remounted the engine. I located an old photo of its installation and reconnected them accordingly. But I also found that the battery isolator was leaking nasty sticky brown goo, and the label on the front has become distorted with heat. I attach a picture. Even after reconnecting the Scheiber unit, it's too hot to hold. (Well it does have a huge heat sink I suppose...)

Separately, the black relay towards the bottom right of the second photo is very warm - I don't know if this is OK.

My questions are:

* What should I replace the battery isolator with? I guess it's a diode-based regulator, although it has a (disconnected) 4th terminal.
* Would it have overheated because its charging circuit was disconnected - or because it's underpowered for a (perhaps later-fitted) battery bank or alternator? - in which case I should presumably uprate it.
* Is it worth replacing it with a FET battery isolator - or would that require adjusting something else to change the charge voltage?
* Is it OK that the black relay in the pair of relays is running warm?​

25 years ago I studied electronics; you can talk techie to me and I'll largely get it although I'm way out of date and don't pretend to understand charge regulation. Very grateful for any assistance.

View attachment 58239View attachment 58240

 

[NickRobinson]

Looks like a VSR ...... That link says its for max 300Ah, you say you've got 575Ah?

Lorsque la tension commune de ces deux batteries atteindra 12,7V (V ± 0,1),la batterie principale se déconnectera. La consommation des diverses utilisations se fera alors uniquement sur la batterie auxiliaire.

 

[BelleSerene]

Looks like a VSR ...... That link says its for max 300Ah, you say you've got 575Ah?

Lorsque la tension commune de ces deux batteries atteindra 12,7V (V ± 0,1),la batterie principale se déconnectera. La consommation des diverses utilisations se fera alors uniquement sur la batterie auxiliaire.

Thanks - well you've helped me find some documentation on that discontinued device, here: http://www.ascadplon.org/wordpress/telecharge/Fiches_Techniques/Bateau/repartiteur de charge.PDF

But it does seem to me it's a diode device as it says 'it has an inherent voltage drop of typically 0.7-0.8V'

Yes, seems underpowered certainly for my alternator (80A vs this device max 70A) - don't know for the batteries; this spec just says max charge 50A.

Does this help?

 

[NickRobinson]

Thanks - well you've helped me find some documentation on that discontinued device, here: http://www.ascadplon.org/wordpress/telecharge/Fiches_Techniques/Bateau/repartiteur de charge.PDF

But it does seem to me it's a diode device as it says 'it has an inherent voltage drop of typically 0.7-0.8V'

Yes, seems underpowered certainly for my alternator (80A vs this device max 70A) - don't know for the batteries; this spec just says max charge 50A.

Does this help?

Sounds like a diode splitter with that drop. I think the item in the French pdf must be something else then. BTW, my Sterling diode thing has large heat sink/cooling fins like the one in your later link

 

[pvb]

You seem to have an unnecessarily complex system, with both a diode splitter and a VSR-type relay system. I'd strip out the diode splitter and the relay system, and replace them with either a new diode splitter (low loss, ideally) or a new VSR.

For a new diode splitter, consider a Sterling ProSplit D in 90A rating (around £45), or go for a low-loss electronic splitter such as the Sterling ProSplit R in 120A rating (about £100).

For a new VSR, consider a BEP relay.