Exactly what is a dc to dc charger?

[shadowmoss]

I have a degree in this stuff (a few decades ago), and I've been reading and interested in the electronics side of things for several years now.  I know how things work.  However, I'm finding that things that I know what they do now go by different names.  I have come to the (possibly incorrect) conclusion that a dc to dc 'charger' is what I know as a battery isolator that is put between two batteries to keep either one from drawing the other down past a set voltage, but sharing voltage above that point.  Am I right or wrong?  This term seemed to take over discussions a couple of years ago, and I never hear the term isolator now.

[rvpopeye]

It's an isolator with extras.
Link to a Victron with descriptions of functions.

https://www.amazon.com/Generic-DC-DC-Charger-Victron-ORI121217040/dp/B0CWYWQGBF/ref=sr_1_2?crid=33NNH5N4WJ9GF&dib=eyJ2IjoiMSJ9.rzRLwb_Kriy4uAWzSWfsbEQIIOAmQpLXTlEgTwu4EcE5rDVyDYuUvi011X_79taWF_iKFublo8yIwTuMEXGrU6OGHXeBIL24Xc7kKihEdzFpAXmyPmJFtL1iRvjdtSFjOpfJJFUUWVkp8xgv4B6x1Ezi6yYlBeHvmfTnwSBqhuTcyNcaNwp-2fihk3IgRNpIf47P6CK-0vejPGKEhxiAGpsarQQlYY1Dt3a6Qhx2VdDWwpN5F9s1uRDL-thuLH77Recx7FbnOnCBxwPDlxsRSEdiN6XSHblFfJkQbLY13LM.QU12A0P2DPlYVWvS_MsSOIqzmLUlWivFH8XYFYNv0xo&dib_tag=se&keywords=victron+dc+to+dc+charger+12v&qid=1728869749&sprefix=victron%2Caps%2C322&sr=8-2

[shadowmoss]

Aaaah, man.  I wanted someone to spoon feed it to me.  Now I have to click and read and decipher and all that.

  (ummm, that is a smiley face, isn't it?  Too many options these days.

[rvpopeye]

The simple explanation ?
They're pretty expensive and you probably don't need one if you have enough solar.
Spoon fed ?well....
Here's some plain oatmeal .
Besides charging your house battery from the alternator and connecting/disconnecting like an isolator.
You can adjust the charge voltage with your phone.
It protects fancy new alternators from things like overloads and other marketing buzzword gremlins.
I'm just guessing but lithium might not like what the vehicle computer is charging the lead acid or other battery charge profiles, maybe it adapts for that too ?
sorry that's all I have in my data base on them..I don't have one .
Downloading manuals is pretty easy these days if you do want to get one.
OR you could just click on that link. I picked at random so others may do more or less according to cost.

[shadowmoss]

Ok, something something enough solar something something lithium via vehicle alternator something something probably don't need.

Thanks, got it.  That actually was what I needed. 

[mudbunny]

The price tag is what scared me. Victron is probably the Cadilac of dc-dc chargers but I have a Chevrolet wallet. I'll be sticking with my continuous duty solenoid. No bells and whistles but it works. Maybe not so much with lithium but my sla battery keeps on charging and discharging well.

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[sternwake]

A dc to dc charger is not just an isolator.

It will raise, or lower the vehicle system voltage to levels which will charge depleted house batteries faster.

Modern vehicles do not just seek to hold 14.2v, but will raise.or lower the voltage depending on how it can best affect miles per gallon.

This strategy can boost MPG by a small amount, but is absolutely horrible for a 50% charged battery that needs to get to as high a state of charge as possible while the engine is running.

With Lithium house baTteries, the vehicle votage can spike to over 15v in some situations, which would trigger the high voltage disconnect in the BMS, and this abrupt shutoff can cause transient voltage spikes which have the abiliy to fry electrical components instantly, or cumulatively over time.

On an older vehicle with simple voltage fixed regulation a dc to dc charger can be unnecessary or of little benefit, and potwntially even a detraction of efficacy

On a newer vehicle, it might be the only way to have the alternator actually feed the depleted house battery any signicant current.

[shadowmoss]

Thanks for the added details. Basically, I'm hearing that it is now needed because of lithium batteries. I'm in the information gathering state, where I've been for the past 10 years or so.

[Scott7022]

It is, as per usual, does the tool fit the hole. I installed a 1/0 cable from the alternator to battery. Then from the battery to a fuse and onto the 500amp/hr continuous rated isolator. The isolator connects the engine battery to the under the seat battery (both Optima red tops) when the engine is running. This is also done with an 1/0 cable running through a 120amp circuit breaker. Power then continues back to a 1/0 to 4 gauge distribution block and feeds car stereo and various stuff like my Victron isolated 30 amp DC to DC charger. Because of a design flaw the Dc/DC charger has to be manually turned on via the app. You can run a hard switch if so inclined with the isolated unit. This allows me to wait for a bit before turning on the heavy draw of the isolator. Think cold mornings, with depleted Redtops and belts squeaking.
The other thing an isolated charger lets you do is place the charger next to the batteries so good 4 gauge cable for the long run back to the charger and then more 4 gauge for the short run to the battery. None of this “well my alternator can put out 120amps and thats over 15 feet away so…” guessing crap. The other stuff the Victron can do is smoke before the BMS system takes the hit, regulate the charge from 33 amps down to trickle charge. It’s intelligent and can be set to be very kind to the lithium batteries or any other accumulators (battery) you use. If I’d have been smarter and hooked my one solar panel to the Victron charge controller and to the main engine battery, instead of the under the seat battery it would have been set and forget easy. However that being said, I still like the ability to turn off the charger until the red tops are floating.

I can’t believe how many people forget when parked off grid that parasitic draw on starter batteries will leave ya stranded. Full house batteries but dead engine batteries ?. Hence why I dedicated my one mounted panel to the Engine. However this shows over 14.9 volts and messes with the Victron. Start charging voltage is set to 14.1. AND if I don’t forget to put a fuzed jumper across the isolator as I did forget last time and killed my engine battery. That one solar panel will float the AGMs by noon in crappy weather.

So Nutshell.
Isolators allow less money spent on cables.
Smarter than dumb alternators. And required for so called smart alternators.
Charge batteries without the futz
Can be set to be kind or hard on the batteries.
More convenient.
Will smoke before your BMS is tested.
Pretty much a must have item if using lithium and vehicle charging. Don’t trust me that’s what Will Prowess Says.
Plus a three hour drive is 90 amp/hrs of power plus the sunshine. If you dont have sunshine…


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[Riverman]

The Renogy at $109 works perfect for me, and for thousands of other guys.

https://www.amazon.com/s?k=dc+to+dc+charger&crid=30I90SBZIC8II&sprefix=dc+to+dc+charger%2Caps%2C456&ref=nb_sb_noss_1

I rather not overload my older alternator with a 40 amp unit.