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Confusion about dc to dc charger


Thumper

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Hey everyone, I'm replacing the old BW6325 with a progressive dynamics with their PD4635. That's what they recommended. And a new house battery, mine is toast. Should I get a dc to dc charger as well or will the current isolator setup be alright? And if I should get one, do I eliminate the isolator. The more I read online the more confused I become. Partly, I think, due to the fact no one is talking about a 36 year old RV. I have a 1986 Sunrader. Thanks

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If your current isolator is working I see no reason to replace it. If it breaks replace it with another isolator. They allow your engine alternator to charge your house battery and your truck battery but when the engine is stopped they protect your house battery from draining your engine battery. The system as made works great. Your new Progressive unit will charge your house battery more efficiently and safe when plugged into shore power. Sounds all good by me

Linda S

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Current isolator setup should be fine, but it will probably fail at some point being as old as it is.

My isolator stopped working in my 80 dolphin and I replaced it with this one from Amazon:

https://www.amazon.com/dp/B001HC6UJ0/ref=cm_sw_r_cp_awdb_imm_PBW632R85K2F4JBB3WF4?_encoding=UTF8&psc=1

 

I also would recommend wiring a switch and running it under your dash to turn your isolator on or off. That way if you totally drain your house battery you have a fail safe to turn off the isolator and you can get your motor started.

 

Also, highly recommend doing a solar setup. I have a 180 watt that really does a great job of keeping the house battery at full charge.  A lot of the time I won't even run the isolator if I'm in an area with great sun, that way it saves my alternator some wear and tear.

 

That, and I have a battery tender if needed. I figured I might at some point and if I'm at a spot with hookups I can charge the battery also. Never needed it yet, though. Its really great to have different options for keeping it charged and no need for hauling around a generator. The only reason I'd ever need that I suppose would be to run my fridge off of, but it does well with propane while boondocking, ac at a site with hookups, and dc while I'm driving..

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Its a fail safe, in case of failure of the isolator.

Also, helps prevent strain on the alternator.

Edited by Ska
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I'm confused about the role of a switch here. I carry a short jumper cable to allow me to connect both batteries together at the isolator, if needed. This is useful in two ways: 

- allows me to jump the engine from the coach battery if the cab battery is flat.

- allows me to charge the cab battery while plugged in to shore power.

 

Are suggesting a switch to do the same thing? The only problem I see is that you would either need some heavy duty cables or the added complication of a relay. While I like the idea I'm not sure it offers anything that my jumper cable solution does not offer. 

 

Also, I don't see how this would reduce the strain on the alternator? 

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I'm not an expert, but what I've been told is that typically the alternator in the truck is meant to have a specific load (one battery). When you add an extra battery it puts a heavier load on the alternator, and then shortens the life of the alternator. Again, I'm not an expert but this makes sense to me.

The switch is a redundancy, I like redundancies. If I have manual control over the charging of my house battery I feel better about the whole situation. My solar keeps the house battery tended well, and if I don't need to charge it with the alternator I prefer not to.

The isolator should keep the house battery from draining the starting battery, but my experience has been that as soon as you turn the key to on, before the engine starts, the batteries level out to each other. Maybe its not wired correctly, but its wired up exactly as stated in the product's instructions, so idk.

Edited by Ska
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"Just the Facts Jack" Alternator "strain"

No matter how you setup the isolator, sooner or later the alternator will have to recharge the depleted house battery. The truck battery will recharge very quickly. The house battery will take many hours. Unless you have a big solar setup.

The basic math, stock Toyota Alternator is 45 or 60 amps depending on what year the truck is. It takes 10 amps to run a carbed engine and 20 amps for an EFI.

Driving at night takes 15+ amps to run all the outside lights. Whats left charges the batteries. With a 100AH house battery drained to the safe limit of 50%, the leftover 20 amp capacity of the alternator will take 2.5+ hours to recharge the house battery.

Still paranoid about your house battery and alternator.

1st answer, lots of reading...https://www.hellroaring.com/index.php

Another plan..https://www.ebay.com/itm/254915540688?hash=item3b5a2676d0:g:MMkAAOSwLpNgW9ot.

You would be looking at several hours for the batteries to equalize their voltage and they are only connected for seconds until the truck starts

With an old style non-diode isolator the connector voltage comes from an switched source. When you actually start the engine the ignition switch cuts off all switched voltage so that max battery power goes to the starter. The isolator drops off line, until after the truck starts and you turn the key to run.

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  • 2 weeks later...

Thanks everyone. I appreciate the info. Did some more reading online, in addition to these posts. Looks like the only time a dc-dc charger is needed is if a lithium battery is involved. Thanks again, love this site.

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