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Old 04-02-2022, 11:59 PM   #1
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Max amp dc to dc charger for 5.4 owners

I just upgraded to a 300 ah lithium. Renogy solar mppt and new wiring fuse boxes ect. I removed the old isolator and agm battery under the frame for this 300 ah lithium beast of a battery

I installed a 40 amp Reno by dc to dc charger and I believe it is pulling too much power from the alternator as I get voltage drop on the starter battery as I am driving from 14.4 down to 13 and even 12.

Is the 40 amp dc to dc charger too powerful for the 5.4. I’m assuming I have the stock 130 amp alternator.

Should I downgrade the dc to dc charger to a 20 amp version or get a higher output alternator?

Anyone know if I am correct in saying the 5.4 stock alternator is 130 amp. That’s pretty small in todays world.
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Old 04-03-2022, 07:38 AM   #2
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I've replaced maybe 4 stock alternators and used the 130 amp versions always. Whether they're off the shelf OEM, NAPA or my trusted rebuilder we've always spec'd that version.

None of my E-Series had any sort of upgraded electrical systems so the 130 amps were always enough.
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Old 04-03-2022, 09:49 AM   #3
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Being as the Renogy 40 amp DC to DC charger can pul 45 to 55 amps, you will need make sure that your alternator can supply an extra 55 amps at worst case operation.

My suspicion is that you are seeing your voltage drop when sitting at a stop light or in idle condition. The output of the alternator is almost cut in half at idle.


Being that your unit doesn't appear to have a programable output, your options are limited. Use a lower 20 amp version, or programable unit or get a larger output alternator.

I generally try to create a worse case load when installing, and check under a low idle condition.


Seeing as you have a 300 amp battery bank. I would recommend getting a larger alternator.

-greg
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Old 04-03-2022, 09:57 AM   #4
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I have gone ahead and purchased the 20 amp version. I’m hopping to not have to install a new alternator with this. I’ll get less charge while underway. But hopefully have a healthy alternator
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Old 04-03-2022, 11:25 AM   #5
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I went through the same decision process last year for a 40A Renogy DC to DC for a 200 Amp-hr lithium system. I asked questions here and searched the web to determine a path forward. Scalf77 (greg) suggested upgrading the alternator and I also thought that was "overkill" but later changed my mind.

I went on to try and design an adaptive controller to switch the DC-DC between 40-20 and Off adaptively based on Sensed alternator temperature using an Arduino with the display.

The basic issue is that at 40 amps while being a reasonable load at RPM/speed, is too much for a standard alternator at idle. This is the reason in a nutshell (similar to Greg's numbers).

If the DC to DC is outputting 40Amps at idle (12V at the battery and 14 amps to the Lithium) then it needs to input about 40*(14/12)*1.2=56A into DC-DC. The 1.2 is a power conversion efficiency number and the 14/12 is the current increase due to the DC-DC voltage boost (12V in 14v out).

Still worse is the fact that depending upon the alternator's efficiency (Victron claims 50%) then you would need to be generating 50% of your output power in excess heat. If we just assume 80% efficiency then this is equivalent to 67 amps. So idling is a worst-case situation that will overheat the stock alternator that otherwise at highway RPMs would be fine. If you lose a volt in cable voltage drop from DC to DC from the Alternator then you are at 40*14/(12-1)*1.2*1.2=73 amps (Equiv )

So while I was dismissive of the "larger Alternator" idea, when I saw the enhanced electronic controls of this alternator at a very reasonable price I jumped on it and feel comfortable that the alternator thermal limits will keep me from getting into trouble even if I forget about manually controlling the DC as stated above.

"This Is Truly A High Amp Premium Quality Well Built Alternator
It Has OE compliant functions : current limiting, thermal shutdown,
load dump protection, shorted field & lamp circuit protection"



https://www.ebay.com/itm/202513986004
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Old 04-04-2022, 12:57 AM   #6
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So I take it that this alternator upgrade will allow me to keep my 40amp charger. Any issues with installation of this 300 amp beast?

Upon searching through the eBay add. Apparently it’s not compatible with my 2013. E350. It’s good for the earlier vans. Do they make one for a 2013 ?
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Old 04-04-2022, 09:36 AM   #7
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Rock Auto shows several 155 amps and a few 225 amp alternators for your van.

https://www.rockauto.com/en/catalog/...generator,2412
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Old 04-04-2022, 09:41 AM   #8
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Quote:
Originally Posted by Lcavalletti View Post
So I take it that this alternator upgrade will allow me to keep my 40amp charger. Any issues with installation of this 300 amp beast?

Upon searching through the eBay add. Apparently it’s not compatible with my 2013. E350. It’s good for the earlier vans. Do they make one for a 2013 ?
I don't know about later models; there are many aftermarket alternators. This one just stood out because of the advanced electronics.

The electronics provide a fail-safe in that if it goes too hot it will limit the current. They are defined as OE function which is entirely contained in the electronics module at the back of the alternator so look for that if you need to find another. Unfortunately, I did not see any other alternator listed that spelled that out. It is possible it is just so standard that nobody actually spells it out.

It Has OE compliant functions : current limiting, thermal shutdown,
load dump protection, shorted field & lamp circuit protection"


Even with an upgraded alternator, I would use a switch to activate the charging. For example, if your battery were to be low and the charger starts because of a Key ON condition you don't want to be fighting the alternator drag and load while starting.

On the Renology you have two inputs :
D+ control charging
LC enables 1/2 current mode

https://www.renogy.com/content/RNG-D...060-Manual.pdf

So either use two toggle switches or I was planning on using one of these.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If you have driver's seat switch and a Haus battery volt meter you will be able to monitor and control your changing while driving.
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Old 04-04-2022, 10:51 AM   #9
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Rock Auto shows several 155 amps and a few 225 amp alternators for your van.

https://www.rockauto.com/en/catalog/...generator,2412

I went to DB Electrical's website and this is the only one listed for a 2013

https://www.dbelectrical.com/product...-12-13-14.html

There is a massive heat sink on the back, but it can still get heat soaked based on the environment and the thermal mass. But I would gather these also have OEM type electronics sophistication of modern "smart alternators" although this one is only 120 amps.
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Old 04-04-2022, 11:40 AM   #10
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I've been using this https://www.renogy.com/dcc50s-12v-50...ger-with-mppt/ for a little over a year in the PNW where it doesn't get that hot without any issues !, Sometimes at night I run my 30amp light bar, no problem.
That pin is optional, as long as you connect alt+ it WILL work
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