diy solar

diy solar

DC-DC charger (B2B) options and general discussion

sshibly said:
It does not matter how big your system is,
Think current limiting device.
You need to work backwards and figure out your max Amps.

My transit van as 60amp CCP behind the driver seat, and I plan on putting the batts few feet away. Even though I have 60a (not sure what rpm I need though). I am putting in a 13A CC CV charger so my draw will NEVER to more than 200W with efficiency loss.

You can connect 2 13A 13.8v chargers to each of your banks and turn on your high idle switch and smoke your fav cigar while you wait for the batts to charge.

FYI: I love your Lance TCs :)
Click to expand...
Thanks. I think when I work backward even this large setup will only run and air conditioner for 2 hrs and of course going way smaller makes A/C during the summer impossible unless I spend 2-3k to install the highest SEER rated minisplit on the market. 800ah / 26A = 30.7 hrs. There not enough time in a day to charge all 800ah on my LiFeON4 batteries at that rate even if I smoke a whole box of cigars. LOL
 
MetalChef said:
Thanks. I think when I work backward even this large setup will only run and air conditioner for 2 hrs and of course going way smaller makes A/C during the summer impossible unless I spend 2-3k to install the highest SEER rated minisplit on the market. 800ah / 26A = 30.7 hrs. There not enough time in a day to charge all 800ah on my LiFeON4 batteries at that rate even if I smoke a whole box of cigars. LOL
Click to expand...
lol, I have gone through that very iteration many many times with my Fourwheel camper grandby and gave up, threw in my box of cubans.
Sir you need a DC APU, no it ain't the Simpson's character!

They make diesel/gas DC APU for DOD, last time I priced em, I found prices starting at $10k :oops:
If you had a 100A @ 13.8 volts, you could charge em batteries in a zip.
Maybe, I mean a remote maybe, you can sit outside when it is hot? :)

This very reason and few other, I opted for a Transit Van with high top with a rear a/c, gasser,
I have 500 idle hours on the engine, go figure. No APU, no battery, no extra fuel can, and no ex-girlfriend to watch my batteries while they charge!.

Now I can smoke my cigar in peace, if I am cold I just press my remote starter and the ford fires up and magically heats/cools the van.

back on topic:
You could get a small genny and run it to juice up the batts, the inverter batts are quite quiet and efficient.
 
We had been chatting about the Renogy DC-DC MPPT 30 or 50. I saw some comments that the unit limits current if solar is providing current. Here is the relevant info in the manual.

I was thinking about the 30 but based on this I am now looking at the 50. I was worried I would tax my 90 amp alternator and damage it. Based on this perhaps not.

comments or other solutions?
 

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DerpsyDoodler said:
It seems like there are very few options for 24v dc-dc and the ones that do exist are absurdly expensive. Does anyone have insight on this or recommendations on ways around it? I have both 12 and 24v source I can tap into but it seems absurd to have to step up to 24v to be able to charge when my chassis batteries already function as both a 12v and 24v bank. I suppose I could put an isolator in place then use either a pwm or other charge controller to regulate charging to the house lifepo4s. Are there any potential pitfalls to doing something like this? Of course, I have not priced that approach. Could be that it isn’t any cheaper than purchasing one of the more expensive 24v units.
Click to expand...
www.donrowe.com

KISAE DMT2430 Abso 30A, 24V DC-DC Battery Charger | DonRowe.com

KISAE DMT2430 Abso 30A, 24V DC-DC Battery Charger is a multi-stage, multi-input battery charger capable of charging different types of batteries commonly installed in boats, RV's, 4WD's and commercial vehicles.
www.donrowe.com

This one is 24v. I can't seem to find it anywhere else and it's not even on Kisae's website, so I don't know if it's too new or discontinued already???

I do see in the manual (pg. 10) that the Kisae's only charge from one or the other input, but not both at the same time. It is auto-switching with preference given to the alternator input. You would have to manually turn off the alternator input with the ignition switch input if you wanted to only charge with solar while driving.
 
Kman said:
www.donrowe.com

KISAE DMT2430 Abso 30A, 24V DC-DC Battery Charger | DonRowe.com

KISAE DMT2430 Abso 30A, 24V DC-DC Battery Charger is a multi-stage, multi-input battery charger capable of charging different types of batteries commonly installed in boats, RV's, 4WD's and commercial vehicles.
www.donrowe.com

This one is 24v. I can't seem to find it anywhere else and it's not even on Kisae's website, so I don't know if it's too new or discontinued already???

I do see in the manual (pg. 10) that the Kisae's only charge from one or the other input, but not both at the same time. It is auto-switching with preference given to the alternator input. You would have to manually turn off the alternator input with the ignition switch input if you wanted to only charge with solar while driving.
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Thanks, I found this, as well, but it’s only 30a (for still yet an absurd cost). ive decided that since the inverter I will buy also has a charging input to feed from a solar charge controller, I will buy an isolator and a buck boost converter to step the alternator voltage up a bit (to proper voltage for LFP), and plug the line into the “solar” input of the inverter. I haven’t fully done the research to confirm it’s appropriate to use the solar input for this, but it seems feasible. IIRC, on my inverter side it’s just a pwm controller that works in tandem with shore power to charge batteries.
 
DerpsyDoodler said:
Thanks, I found this, as well, but it’s only 30a (for still yet an absurd cost).
Click to expand...
Remember this is 30A @ 24V so this is actually delivering more power than most of the other options on the list. As to cost, $350 doesn't seem tooo painful for a dual input charger, though it is more than I would like it to be :) .

DerpsyDoodler said:
ive decided that since the inverter I will buy also has a charging input to feed from a solar charge controller, I will buy an isolator and a buck boost converter to step the alternator voltage up a bit (to proper voltage for LFP), and plug the line into the “solar” input of the inverter. I haven’t fully done the research to confirm it’s appropriate to use the solar input for this, but it seems feasible. IIRC, on my inverter side it’s just a pwm controller that works in tandem with shore power to charge batteries.
Click to expand...
Have you found a suitable Buck/Boost converter?
What inverter/charger?
 
Samlex EVO 4024. But I would still have to limit input current on that port to 50a max.

edit: Pressed save before I finished. Just starting to look at boost converters, now.
 
Dzl said:
...As to cost, $350 ...
Click to expand...
Right, except I don’t need/want dual input. I just want to charge from the alternator at 24v. Seems simple to me. It’s been several days since I’ve given this dilemma attention, btw.

it’s not clear to me exactly how the inverter/charger handles the input. Does it condition it? Does it do dc-dc conversion according to its charger settings? Seems like it would need to in order to combine it with its own ac charging output (see samlex documentation for clarification on that statement).

 
I would pay the $350 for this, if it did more than 20amp in dc-dc mode. Other uses I value as opposed to just a permanent fixture for alternator charging. seems like a nice dc power supply as well as ac-dc and dc-dc charger...

12S 40A AC balance charger

12S 40A AC balance charger
www.chargerystore.com www.chargerystore.com
 
Dzl said:
Have you found a suitable Buck/Boost converter?
Click to expand...
considering this:

Amazon.com: DC-DC Converter Module Boost DC Step Up Voltage Regulator CC CV Stabilizer Power Supply Module 10-60V to 12-97V 1500W 30A: Computers & Accessories

Buy DC-DC Converter Module Boost DC Step Up Voltage Regulator CC CV Stabilizer Power Supply Module 10-60V to 12-97V 1500W 30A: Power Converters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com

it’s not isolated. i don’t think that will matter for my installation, but I’m not entirely clear on this point, yet. I don’t fully understand the how’s or why related to isolation or how it applies to my build.
 
Eh...the more I think about this, the more I come to the conclusion that my idea (using external charging input on inverter) won’t be feasible. It either operates in inverter mode or charging mode. Will it take the supplied power from the external charger to be used for inverting power when in inverting mode? Based on how the manual reads, it is not clear. The inverter will not “charge” while inverting, but that doesn’t mean it couldn’t use power feed from external charging to push into inverting. We’re that the case, then this feed could power the inverter load from alternator while my actual solar charge controllers supply charging power to the batteries. Frankly, I feel like I’m running into too many roadblocks and ifs, maybes, buts with this route. What I would love is a device like the chargery I posted, which can double as 40amp dc-dc and ac-dc charger, as well as a stand-alone bench power supply. In leu of that, all I want is a reliable, single purpose 24v dc dc charger at a price that reflects exactly just that.
 
DerpsyDoodler said:
Click to expand...
wondering if someone can read section 5.4 in the manual and tell me how they interpret the function of the external solar charging input.

I interpret as external scc is fed directly to the battery terminals (through a shunt) regardless of operating in inverting or charging mode. This is what I would expect, but don’t want to take this for granted.

can anyone confirm this or do I need to call samlex support?
 
Hi guys, I'm about to build a system for a large overlanding rig (going full electric with creature comforts) and this looks like it was my biggest blind spot - I was expecting to be able to recharge quickly while driving. I have a 300A alternator so surely I charge my batteries quickly and with minimal equipment while driving right? ?

Looks like I'll be going 24v so that adds even more complication... Besides the price, any reason this beasty in 100A isn't mentioned? https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a

Do we really need any sort of fancy charging setup anyways? Why not just run a DC - DC booster with adjustable output voltage (a fancier version of what DerpsyDoodler mentioned) like this: https://www.daygreen.com/collection...up-adjustable-booster?variant=32658880659503?
 
geoffire said:
Hi guys, I'm about to build a system for a large overlanding rig (going full electric with creature comforts) and this looks like it was my biggest blind spot - I was expecting to be able to recharge quickly while driving. I have a 300A alternator so surely I charge my batteries quickly and with minimal equipment while driving right? ?

Looks like I'll be going 24v so that adds even more complication... Besides the price, any reason this beasty in 100A isn't mentioned? https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a

Do we really need any sort of fancy charging setup anyways? Why not just run a DC - DC booster with adjustable output voltage (a fancier version of what DerpsyDoodler mentioned) like this: https://www.daygreen.com/collection...up-adjustable-booster?variant=32658880659503?
Click to expand...
What type of batteries and how big is the bank?
 
Yuphorya said:
What type of batteries and how big is the bank?
Click to expand...
I ordered 17 (1 spare) 280Ah LiFePO4 cells, so 8s2p for 24v 560AH (13.44kw). That big Victron maxes out at 50a to 24v so even that is basically a trickle for this setup (12+ hours to fully charge?). We're a family of 4 and planning on a full kitchen with induction cooktop, microwave, electric cabin+water heat, possibly AC, lots of electronics...

We're not planning extended stays in any one location (overlanding) so was hoping a couple hour drive would be enough to recharge each days use. We'll see how that goes, I'm guessing we'll start settling in places and need a ton of solar later, but I know we'll be driving a lot at first. I debated a coolant heater + exchangers for heat, but with the large battery I figured we can go full electric instead. That's a lot of power to replace every day however.
 
Reed Cole said:
2. The Renogy dual input charger when the engine is running will allow for a maximum of 25A from both inputs, even if you are only getting a few amps from the solar. A switch to disconnect the solar panels is recommended so you can prioritize alternator charging when you need it on cloudy days.

The wording in the Kisae manual is a little vague, but I think it just switches between the solar input and alternator input depending on if the alternator is running.
Click to expand...
As I understand the Kisae, if you connect the ignition sense wire it will not drain the starter battery, only charges when engine is running.
 
Hmm, I can get a dual alternator kit, but 24v looks to require some major hacking and $$$ for a good one, and I'm seeing crap output at low speeds (idle). 12v is looking more appealing.

Still, rather than DC-DC why not a dedicated 2nd alternator with a regulator built for charging batteries? Seems way better.
 
geoffire said:
Hi guys, I'm about to build a system for a large overlanding rig (going full electric with creature comforts) and this looks like it was my biggest blind spot - I was expecting to be able to recharge quickly while driving. I have a 300A alternator so surely I charge my batteries quickly and with minimal equipment while driving right? ?

Looks like I'll be going 24v so that adds even more complication... Besides the price, any reason this beasty in 100A isn't mentioned? https://www.victronenergy.com/dc-dc-converters/buck-boost-dc-dc-converter-25a-50a

Do we really need any sort of fancy charging setup anyways? Why not just run a DC - DC booster with adjustable output voltage (a fancier version of what DerpsyDoodler mentioned) like this: https://www.daygreen.com/collection...up-adjustable-booster?variant=32658880659503?
Click to expand...
As far as I understand, the DC-DC converter you linked to is an option.
As to why it is not included in the spreadsheet, it is because it is not a DC-DC charger. There is a Victron video adressing this somewhere. For now at least, I chose to limit the table to DC-DC chargers explicitly designed for charging a battery from the vehicles charging system.

There are at least 3 other methods I am aware of that are not included here (1) External regulators (2) simpler DC-DC converters (3) devices that implement some sort of duty cycle 10 min on / 10 min off for example to reduce head / stress on alternator. Eventually I would like to cover these types of devices here or elsewhere, and am happy to have them be part of the conversation, but for now am not going to add them to the table.

I chose to focus on DC-DC chargers first because (1) they were designed explicitly for use with vehicle charging systems (2) they are the most popular solution currently (3) there are a manageable number of brands/products to cover (4) they are reasonably affordable and reasonably simple to setup.
 
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