Help! Need high current boost converter

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Mikethezipper

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Jul 7, 2018
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I'm living in a van with my diy 16v 5.4kwh 4s100p battery pack. The issue I have is I can't seem to charge it. I foolishly thought I could parallel two 1800w boost converters, but of course I was wrong. I cannot seem to find any commercially available high amperage boost converters that output anything close enough to what I need. The highest output I can find is the 20a boost converter I already have, and at that charge rate I would need my engine to run over ten hours to charge the battery.

How are other people using an alternator to charge lithium batteries?
 
That's the problem with 4s config with a regular lithium. The 3.7 nominal just doesn't fit 12V. A LFP/LiFePO4 at 3.2V nominal fits the 12V better and you have more options. SO either go 24V or lose the voltage.

In any case Victron makes some DC-DC stuff, so check there to see if anything fits your bill. Just remember a straight converter won't work unless it's a charger as well, so it's capable of tapering the current (cc/cv).

https://www.victronenergy.com/dc-dc-converters
 
Yeah, I looked at their products and found a single $1200 solution. I mean it sure fits the bill from an application standpoint, but at $1200 i don't see how that financially makes sense for anyone.

For this particular situation, I don't have the ability of converting to 24v since I can't break apart my pack without finding someone to take me in for a week while I rebuild my pack from scratch. The other issue i had was that a 6s system trips the undervoltage protection on every inverter i can find. But if I run at 7s now i am back in the same boat....

Is there a way to modify something (either a dc-dc converter in or even an inverter) to get the effective output I'm looking for?
 
Im sad to say that you just experienced the disadvantage of LiIon and 12v... Its better to just bite the apple and redo it properly :)
 
Except 24v doesn't fix the problem does it? At 6s i can't run an inverter but there are many 24v chargers i can get .. but at 7s which will let me run an inverter i am back to not being able to charge it. At at least I can only charge it at 20amps using my existing boost converter. From y'all's experience can I modify a 24v specific boost converter to output a custom voltage by modifying the feedback loop? Or are the electronics designed such that modifying that throws everything else into a loop and it won't work right?
 
Most of them are designed by a purpose yes. If you have the electronics knowledge you can modify it else i wouldnt care.

You can of course get converters of any kind and if they dont exist you can get them made. For charging you can parallel many inverters thats not a problem as such. Since i dont know the input voltage to charge your 4s system from its hard to give examples. 7s is spot on for 24V systems including normal chargers in that range! I dont know a single 24V charger that doesnt cope with the full 24V range from the start.

Is it from normal 12V? Or other? You talk about Boost...
Boosting from a car system to charge a 4s bank is harder since they cross the voltage ranges and require a Buck/boost or boost/buck converter. Basically you need 2 converters

You can for instance make one your self by using a Inverter to AC then going back to DC and charging. You can use an iCharger in that combo and push 70A in to it.... Or any meanwell like PSU

This PSU can do 100A output up to 16.5V and you can parallel as many as you want....
You have the datasheet here

And yes when we start to talk about higher currents and special voltages it will cost you. Above PSU can also take DC as input but you still need to get the current voltage to it.
 
Thanks daromer!

My battery bank is in a vehicle with a 12v system. So the alternator outputs 13-14.2v or so. The issue that I have is most chargers step down the voltage whereas I need to bump it up. Some companies do make dedicated boost chargers for 12 to>24v systems for automotive, but they are cost prohibitive at $1k +. I know this stuff isn't cheap, but that's just too much. I actually have an AC to DC meanwell power supply for 16v, 55A that I bought if I couldn't find a method to modify a dc to dc boost converter to accomplish the task. I'd rather not sacrifice both an additional inverter and the efficiency to do it all that way.
One of the units I'm looking at is:
https://www.amazon.com/dp/B07P41HCV2/ref=cm_sw_r_cp_apa_fabt1_0YgTFb81DA1DP
They offer a 50amp one for a slightly more affordable $180 or so. I've been looking at the Chinese boost converters I have and all the markings on the ICs are gone, so I'm concerned that without that information I'll find it harder to reverse engineer the circuit to find the voltage feedback and add a voltage divider. Does anyone have experience with units like this?
 
You cant boost your car system to charge a 4s lithium bank unless either your car system is empty or the lithium system is full. You need a 2 stage sytem that boost-buck or buck-boost as i said.

You can get high efficiency here but it will cost you. As we have said from the start it is doable but it will be costly. Its easier to rethink the setup instead unless you want to pay for it.

Best option is to have a larger swing between input and output if you want to stick to single-stage system.
 
Your missing a trick....

You only need a 3.3V isolated power source (buck)

Connect the DC output to the -ve battery and feed the +v from the van to the -ve output of the (one or more in parallel) isolated buck units....
13.2V + 3.3V == 16.5V

There is a board on aliexpress that is a 35A buck from 18-36V.....
https://www.aliexpress.com/item/4000088930622.html

Use the boost controller you have to step up the 12V to say 36V and feed it into one of the 35A units, you can then charge the whole system at 35A. Add a second board in parallel on the 36V output to get around 60A charge rate (your alternater will likely reach it's limit way before then on idle).

The power/energy limit is the single boost converter 13.2V at 20A input = 264W in and output at 3.3V with loses (20%) of 211W which at 3.3V == 64A

Separate thought, charging from your engine is very inefficient overall and would likely cost around $1 per kWh

I had to charge from the truck a few times a while back (when I was on 24V with lead-acid) and even tried a 12V inverter - 230V - power supply route to get a higher current.

If your fixed with the van for a while, maybe swap the alternator for a 24V model (truck) and then rig up a CC/CV buck for the 12V battery (similar units to the one above) and then a buck only charge route.

Another option - remove the regulator in the alternator and draw out the higher AC or DC voltage..

Another option - create a really large coil the size of the van roof, then park under a HV line...
 
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