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Electric - Alt to Battery vs Battery to Battery Charger
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chrismsnt
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PostPosted: Tue Jan 26, 2021 1:23 pm    Post subject: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Okay... question of the day... what's the difference of a Alt to B charger vs B2B? My van came with a Sterling Alt Pro C (Alt to B) charger however I'm starting to rewire and build for solar. Now when referencing what everyone is doing, they have the alt wired to starter battery and then have the B2B charger coming off of the starter battery. This is the one video I keep going back to because it's easy for me to digest (https://youtu.be/NImNGe_3TYk) . Thoughts anyone?
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fxr
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PostPosted: Tue Jan 26, 2021 1:48 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

I'll be taking the feed for the Aux charger (DCC50S) straight from the alternator, with the alternator's sense wire connected directly to the starter battery. Best of both worlds. The starter battery gets the proper voltage, the aux battery gets the maximum charging current that it wants.
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MarkWard
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PostPosted: Tue Jan 26, 2021 3:29 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Some of your abbreviations are tripping me up. As long as the cabling is sized properly, BAT power is the same at the starter solenoid, alternator bat post or the starter battery pos post.

Combining and isolating are the challenges. I used an automatic system, but when it failed I opted for a manual Marine Battery switch. It’s cabled so I can start off either battery or combined. In storage, both batteries are disconnected at the switch. Camped, only the house battery is on. Driving both batteries are combined to be charged by the alternator.

I have a permanent charger connected to both batteries before my switch so both batteries charge independent. I have no use for solar at this point, but seems it would be easy to add.
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PostPosted: Tue Jan 26, 2021 3:46 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

It also matters what the battery chemistry is. Some batteries will not charge fully on a direct alternator connection, they need a DC/DC charger to deliver the correct charge profile.
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fxr
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PostPosted: Tue Jan 26, 2021 4:00 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

MarkWard wrote:
Some of your abbreviations are tripping me up. As long as the cabling is sized properly, BAT power is the same at the starter solenoid, alternator bat post or the starter battery pos post.

Not necessarily so.

Consider a large LiFePo4 battery connected (via a DC-DC charger, 'natch) to the starter battery. If the LI battery draws 50A and the starter battery wants 10A then there'll be a 60A current in the starter to starter battery cable. There *will* be a considerable voltage drop, which the alternator may compensate for, depending on wiring and type, granted, but this will inevitably be an extra strain on that system, especially any connections.

It'd be far better to separate those currents, surely.
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MarkWard
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PostPosted: Tue Jan 26, 2021 4:03 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

dobryan wrote:
It also matters what the battery chemistry is. Some batteries will not charge fully on a direct alternator connection, they need a DC/DC charger to deliver the correct charge profile.


You have a recommendation? That’s something new to me. My shore battery charger lets me choose a voltage. I’m limited to about 14 volts plus or minus with my alternator.

Edit, I’ll bow out. It’s apparent I did not understand what was being asked. Forgetting all add ons, I stand by the statement that the voltage should be identical at the 3 points I stated. Often it’s ease of installation that dictates the common point.

My house battery is under the back seat and cabled through my battery switch to my starter solenoid. My starter battery is in the engine compartment so my paths are the shortest and easiest for my application.

We have no real battery demands. More of a convenience than a necessity.
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fxr
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PostPosted: Tue Jan 26, 2021 5:19 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

MarkWard wrote:
I stand by the statement that the voltage should be identical at the 3 points I stated

Only when there's no current flowing!
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PostPosted: Tue Jan 26, 2021 5:48 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Hi Chrismsnt:

Here is a dumbed-down explanation of the differences between alternator charging and DC to DC charging. It is dumbed down not for the audience, but because I lack the correct terminology. It is distilled from the information I got with my Redarc DC-DC charger.

A quality DC to DC charger uses MPPT technology "in reverse". For solar charge controllers, the old-school PWM units just "chop off" (not a technical term) the portion of the solar electricity that exceeds the charging voltage requirement of your house battery. The MPPT charge controller uses transformer-like components to reduce voltage and convert that excess voltage into higher current/amperage. In this way, no solar power is wasted.

When you charge your house battery directly from the vehicle's alternator, the battery will only receive the voltage that is available after the charging of the starter battery and any vehicle loads have been accommodated. That voltage, with a number of vehicle loads like fans, rad fans, headlights, etc, can be well below the 14.2 to 14.6 volts that your lead-acid battery needs in order to charge. So, any time that the available voltage is 13.5 volts or less, your house battery is essentially NOT CHARGING.

The DC to DC charger converts available current to higher voltage so that your house battery can actually charge. It also maintains, depending on the settings you apply, a steady voltage to the house battery, which aids in faster and more effective charging. Each time you interrupt charging to the house battery by lowering voltage below the charging voltage, a lead-acid battery requires more charging time to go back to where the charge left off before the interruption.

Most DC to DC chargers can, for those using LiFePo4 batteries, supply the very high currents (provided the alternator can keep up) which LiFePo4 batteries are capable of accepting. This can enable a full re-charge of a LiFePo4 battery in two to four hours of driving, for example. They also typically haver selectable charge profiles for the different battery types which both protect the battery from over-charge damage and charge as quickly as that battery type can do, without damage.
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chrismsnt
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PostPosted: Tue Jan 26, 2021 5:53 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

So... here's two diagrams. It's nuance however, the Alt Charger hangs in between the Alt and batteries vs the Battery to battery charger hangs off of the back side of the starter battery. (1st pic is Alt2Bat and 2nd is Bat2Bat)

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.
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Howesight
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PostPosted: Tue Jan 26, 2021 7:54 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

The Sterling DC to DC charger is listed at $320 USD. The Victron MPPT solar charge controller in the video (https://youtu.be/NImNGe_3TYk) you referred to costs $209.67 on the Amazon link in the video.

That totals $530. Both units are of excellent quality. But Renogy and Redarc make units that combine both solar MPPT charge controllers and DC to DC chargers into one unit. The Amazon reviews make it clear that Renogy has not yet sorted the bugs in their design. ( I note that Will Prowse had no problems with his Renogy unit, but that appears to be sheer luck on his part). Redarc gets 5 star reviews. That is what motivated me to choose the Redarc BCDC1240D DC-DC CHARGER 12V40A. You can find the Redarc units at this link:

https://redarcelectronics.com/products/dual-input-40a-in-vehicle-dc-battery-charger40 amp unit seen at this link:

The Redarc unit is listed at $442.61.

Even if the Redarc were a bit more expensive than the comined cost of the Victron and the Sterling, it is still preferred because it allows BOTH solar charging and alternator chargin at the same time. The Redarc website has PDF downloadable manuals that are written in clear English, a must for me. FWIW, the Victron products also have excellent manuals and similar support. Renogy could learn a lot from these companies.
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PostPosted: Wed Jan 27, 2021 5:08 am    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Many, many more here would be better served by installing manual battery switches and learning how to use their battery systems than relying on $5 of electronics, sold for $50, with the reliability of the Kursk .
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puchfinnland
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PostPosted: Wed Jan 27, 2021 5:54 am    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Second battery is actually quite simple with Lead/agm type

simple continuous duty relay triggered by IGN to connect when engine is running.
Adding an adjustable voltage regulator on the back of the alternator is also a nice inexpensive investment.
the real issue for vanagon owners is how much battery you can fit under the drivers seat, If you are willing to install somewhere else, and want to stick to Lead battery's there an effective choice is a Group 31 AGM deep cycle .

for any future thoughts of AC battery charger or solar choose a dual output charger for charging both start and house (NOCO 20A Dual is a great product)
and solar is straight forward.

lithium is a not as simple.
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chrismsnt
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PostPosted: Wed Jan 27, 2021 8:16 am    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

Thanks everyone for their thoughts and opinions however no one has answered nor addressed the core question: What's the difference between the two?
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space
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PostPosted: Wed Jan 27, 2021 5:06 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

from what i can tell by ur 2 diagrams
the lower diagram has 2 separate BMS systems (hookups)
The upper looks like it has a combined BMS (all in one)
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fxr
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PostPosted: Wed Jan 27, 2021 5:32 pm    Post subject: Re: Electric - Alt to Battery vs Battery to Battery Charger Reply with quote

chrismsnt wrote:
Thanks everyone for their thoughts and opinions however no one has answered nor addressed the core question: What's the difference between the two?
If you mean what's the difference between charging your aux battery directly from the alternator or connecting it directly to the main battery for charging - the only difference is that with the latter the alternator to starter wire and starter to main battery wire will have much more current through them, resulting in a voltage drop. This may (and probably will) cause both the main and aux batteries to take longer to charge. Also, you should really only ever do either if the two batteries are of the same construction and size and preferably of the same age - i.e. identical.

If the two batteries are not identical, and especially if they are of different construction (LiFePo4 vs AGM vs sealed lead-acid vs low-maintenance lead-acid vs flooded lead-acid) then it's best to use a DC to DC charger connected between the alternator and the aux battery.
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