130 Amp alternator question: Biggest DC-DC charger for house battery?

Planning on doing a dual battery setup where my 2nd (house) battery will be a lithium behind the back seat. Also going to upgrade my "big 3" wiring to future-proof and protect things as I add more electrical demands like lights/winch/etcetera. Going to use a Redarc DC-DC charger for the house battery but I realized I'm not sure which one is the largest I can safely use with the 2nd gen 130 Amp alternator.

Searching the forums and online return few usable results but maybe I'm not using the correct search strings... Anyone know how I would be able to find the maximum load that is put on my alternator by all the stock things? Or conversely how do I determine which size (amps) is the largest I can safely use on my system?

I should also metion I will absolutely be upgrading my "big 3" wiring and I'm not opposed to having the alternator upgraded or re-wound (got a local shop that does great work). At this point I'm almost certain that will be necessary but I want to research and make sure - if not needed that's more $$$ I can put towards other projects.

Thanks in advance!

 

Well wouldn't ya know I found some partial answers shortly after I clicked the "post" button. Still very curious to hear what the TacomaWorld hive-mind thinks about this so please do share info so future people can read.

In any event, I found this pretty good, short, clear, concise video from Summit Racing linked below that answers most things: basically 130A might not be enough for what I want (50A DC-DC probably too big for it, 40A borderline, 25A likely just fine); use an amp-clamp with everything turned on to find out loads; and no such thing as too big (that's over-simplified but yeah).

Also found old TW threads with some suggestions for Quality Power, DC Power, and Mechman.com HO alternators. Looks like I'll need an extra $300-400+ to make this happen if I go big unless local shop can rebuild my existing for less...

https://www.tacomaworld.com/threads/quality-power-high-output-alternator.522747/
https://www.tacomaworld.com/threads/alternator-h-output.745212/#post-26539646

https://youtu.be/NS5xJskBtBM

 

So I am working on building an aux battery setup and have been looking at DC2DC chargers and MPPT's for when I add a solar panel in the future. This is my first setup so I have been doing a decent amount of reading. I was under the impression you could get a 30 or 50A DC2DC charger (such as the Renogy DCC30S or DCC50S) and either would work, but the larger one would be able to accept more current and bulk charge your aux battery quicker. Does it just draw on the alternator more and overwork it, or what is bad about running the higher amp DC2DC chargers?

Thanks!

 

It would just be charging one battery?

Stick with the 25amp charger. More amps to the house battery isn't necessarily better.

 

That's exactly what I'm trying to figure out too but seems like I get different answers all across the internet. From what I have read going with the 50A DC-DC charger might be too much for our system (or might prematurely kill the 130A alternator). I don't want a surprise alternator failure when I'm off-grid so in my mind that's a weak point of the system if I do in fact build that DC-DC/Solar setup. So yeah that's why I'm posting here. I would rather not spend $400 for a bigger alternator so I want to see if TacomaWorld experts have more info.

 

That is not true in all cases. I will be using LiFePO4 batteries that can handle high current input ratings. Assuming the house battery only charges from DC-DC and not solar to avoid extra complications, the 50A charger will charge the battery faster than a 25A charger. In this case depending on battery size that can be several hours of difference. Faster charging from bigger DC-DC charger is absolutely better for this application but it comes at a cost (which is apparently $400+).

 

Just curious - What size LiFe bat are you installing? 100 Amp hr? Ignoring the specifics of the charging curves, you are nominally looking at 2 hrs vs 4 hrs for a completely flat battery via a 25A or 50A charger? What do you plan to run of your battery 50, or even 25 amps, continuous is a lot power.

 

Great question. If I go with the "smaller" system it would be the 25A charger with a 100Ah LiFePO4 battery. If I go "bigger" it would be minimum 280Ah DIY battery build with the 50A charger.

Again, removing solar from that equation to keep it simple but yeah solar on top would make it faster depending where I am located (currently in Wisconsin not so good but better if I was in the southwest).

 

whats your standard drive time to support your aux power needs? no reason to crank a battery with 50amp if youre going to drive a few hr to your destination when 25amp will do.

 

Good points here. I live off-grid and just converted from flooded lead-acid batteries to LiFePo4 batteries last week. If you are running at least 100AH then you won't be concerned about charging too quickly in any case. A conservative charge rate is AH capacity/1 or 100 amps for a 100AH battery. I am using EVE 280AH batteries setup for 24v and 560AH and I can't charge faster than 74A if I am mid-day and generator running.

As for your alternator, bigger is better for sure. Another option (my preference) would be to add a second alternator to handle your battery charging needs. You wouldn't need as big of an alternator and it won't kill your truck's electrical system if your alternator fails due to overcurrent. Get a 60A alternator, build a bracket, and get a longer belt.

Keep a 100W solar panel available to supplement your running truck if you plan to stay put for several days.

Lastly, don't let your batteries remain at 100% state of charge. They are happiest around 50%-70%. I have my charge controller setup to transition to float once my batteries hit 75%. My float set point powers my loads through they day without charging or discharging my batteries.

I like off-grid power discussions.

 

https://www.tacomaworld.com/threads...atteries-thread.295653/page-166#post-26890978

Check this out.

@REDARC_Ryan

 

Needs are always variable. There are absolutely reasons to go with 50A over 25A and in my use case 50A would be better if I can swing it without going completely overboard on the effort to do so.

Appreciate the input. All good real-world info for people designing a system. I'm trying to not do a 2nd alternator, would rather pay $400 for a bigger one than go with 2. Again, keeping it (relatively) simple and pseudo-stock. 10-4 on the SoC levels.

Nice info thanks and I forgot we have Redarc members here. Always welcome input from someone like @REDARC_Ryan .

 

What is the demand on the house battery? You need to calculate the cycle time based on drawdown (current load over time) related to runtime for recharge (recovery time). That exposes the amps needed for uptime.

If 99% of the time you are just topping off that is a big difference from drawing down the house battery to cutoff voltage frequently.

Remember you will draw current from the start battery as reserve.

 

Demands on the house battery will vary depending if I go with 100Ah or 280Ah+. Still building my truck and adding fun stuff. Right now plan is to charge drone and camera batteries and possibly a fridge, some lights, standard stuff. Depth of discharge on the LiFePO4 is 100% but I will be setting cutoff at 20% to stay conservative. Possible it will be frequently drawn down that far. Batteries should handle it fine.

House battery will be isolated from starter battery. That's my choice, others might do it different for their needs but I'm sticking isolated. Period.

Great discusion here and I don't want to stop it. Pretty sure I have my answer and learned I should have clarified my main question: What's the biggest DC-DC charger load we can safely put on the Toyota OE 130A alternator (assuming you are already changing the "Big 3" with it)?

 

The main reason I think a second would be better than a bigger alternator is because it would remain stock. Without looking at my truck I can't tell where to mount another alternator, I just know stock parts usually last ages longer than aftermarket or modified parts. Want to undo the modification? Unbolt it and you are done. No permanent changes. But a 200 amp alternator would sure make a good heater in the winter! Haha.

 

Sure but to contrast that there are reasons to not, including alternator capability, more robust wiring, cost, etc. Especially if you can plug into shore power between trips.

 

On the other hand, installing a bigger alternator in the same spot as the original alternator changes nothing from stock (other than what specific alternator is installed at that location). Some use the stock serpentine belt too. That's what I'd be shooting for if I upgrade the alternator but that's just my preference.

I agree but also have settled how I want to do that for my project. Shore power not a factor here, neither is solar. My main questions are strictly around the safe capabilities with stock 130A alternator sizing to the DC-DC charger.

 

I would suggest the smaller 25A charger with the factory alternator. Also, install a 130A breaker to protect it in case.

 

In your list of "things" I don't see any big hitters, I run a similar set of "things." I use a 175W solar panel and keep a 100AH LiFe happy with no DC-DC capability. I can run 4-5 days with zero solar input no worries. Also, don't count on solar making a big contribution compared to the DC-DC charger. Plan on only pulling 70W per 100W of solar, which is on the order of 6A.

Per above, I'd go with a 25A DC-DC and a stock alt. If you are going to add solar, consider going with a Renogy battery and charger. They make a "smart" controller that will utilize solar first and back that with DC-DC as needed - as I understand it this requires a Renogy LiFe smart battery - they are know to make good bats..

 

I have the Renogy DC-DC w/MPPT and it worked flawless while living out of my truck last summer. You can select battery types, I used it with an AGM.

The biggest benefit over the Redarc IMO, is that it charges the starting batter with solar once the house battery is full. Wasn't uncommon to have both batteries fully charged.