Boost converter recommendations, 120VDC

[harrisonpatm]

Wanted to ask this question separately from my build thread in case it's easier to see.

I currently charge my 72v nominal motorcycle from my 14s Li-Ion DIY powerwall, using a boost converter. Input is my home powerwall, I set output to 83.6V, and it works as a CC/CV power supply. Works great, I get a solar-powered motorcycle, and efficient thanks to no DC-AC-DC conversion.

For my upcoming build of 28s Li-Ion, I would like to implement a similar system. Trouble is, it's harder to find off-the-shelf affordable components that are rated for over 100VDC. Currently I use this, but it only goes up to 96V. So far I think my best bet is this that I found on amazon. Goes up to 120v, but only 900w. I don't mind charging slowly, it's better for the battery anyway, but I'd rather stay well under the max rating anyway (say 600W?), and that might be too slow for a 9.5kwh battery. So I could purchase 2-3, and parallel their outputs. That's my best idea so far, but it'd be bulky and might be overcomplicated. Plus there will be conversion losses for each component, I'd rather just have one single component.

I wanted to check the forum first, has anybody seen a 1kw+ rated boost converter that can go up to 120V? Thanks in advance.

 

[amberwolf]

Paralleling may work, as long as the output stages of the units are designed to allow this, or you install a diode in the output wire from each one. It's likely that the total conversion losses from multiple paralleled units will be the same as a single larger unit; you can compare the efficiencies of different models in a series from one manufacturer to verify that.

Alternately:

High voltage is usually harder to find and/or more expensive than high current.

What about splitting the pack input into two separate 2-pin connectors (or a single connector that is three pins, or four), wired each to charge half the pack voltage, and using two isolated-type DC-DCs of each half the voltage?

In this usage the BMS may not behave correctly, since there's no single common negative for it to turn off (it would only turn the lower half charger off), but if it's a contactor-type BMS, it could be wired to use a multipole contactor (or multiple contactors) that disconnect both chargers. (there are a few ways this could be done).

 

[harrisonpatm]

What about splitting the pack input into two separate 2-pin connectors (or a single connector that is three pins, or four), wired each to charge half the pack voltage, and using two isolated-type DC-DCs of each half the voltage?

I thought about this, but half the pack is 14s, and my home system is 14s. Voltages are too close to boost or buck.

 

[stan.distortion]

I thought about this, but half the pack is 14s, and my home system is 14s. Voltages are too close to boost or buck.

Can you just wire them up in parallel and let your home charging system manage things as though it's just extra powerwall capacity? Not sure how inrush would be managed (an empty pack connected to a full powerwall), I'd thought of doing something similar and just using resistors but that's probably a godawful inefficient option.

 

[harrisonpatm]

Perhaps that could work, but I believe it would be too hard to implement on my already-finished build. Maybe for next time. Not a bad idea at all

 

[harrisonpatm]

I got one of these and am in the same situation but haven’t used it yet

Just found this amazing item on AliExpress. Check it out! $24.00 | Factory customized voltage 75~150V to 5V/12V/24V Isolated DC DC Converter

https://a.aliexpress.com/_mNOeqEM

That's a buck converter, not a boost

 

[Hummina Shadeeba]

Sorry wrong thing.

It is hard to find higher voltage stuff as you say. But it’s just ac to dc and I think also not what you’re looking for.

Just found this amazing item on AliExpress. Check it out! $145.00 | Charger 90v 120v 0- 20A 15A Adjustable Charger 140v 134v 126v LI-ION Lithium Lifepo4 Battery Pack Charger LTO

https://a.aliexpress.com/_mLPkRWg

 

[Hummina Shadeeba]

Speaking of other things than you’re talking about but related and maybe a common interest: what do you charge 126v with?

 

[harrisonpatm]

Speaking of other things than you’re talking about but related and maybe a common interest: what do you charge 126v with?

My max charge for my 28s Li-Ion pack is 116.8v