[Caevlist] DC charging

[Allan Hesch]

I think I have the definitive answer to the DC-DC charging question. Seems
like it just isn't worth it and therefore no equipment is made to
accomplish it. Since the power from solar panels is "free", line losses
mean it just takes a little longer to charge using regular DC to AC to DC
equipment.
Thanks everybody for your input.

"He needs to charge the truck as if it was on grid because it will need to
be able to get charged on the grid, if only when it's at the neighbors.
Loaded, it may only make a one way trip into town.

All of his household appliances run off the inverter. The truck is just
another 240VAC or 120VAC appliance that has to be compatible with the
components of the offgrid system.

Most of all, it cannot damage the offgrid system or there's no water coming
out of the well. It's not something to fuck with, as we say in engineering.

For offgrid, the only cost of inefficiency is a larger solar collector.

For an EV, it's just extra charging time.

You don't have a case for DC-DC here that I can see that isn't fantasyland
blue sky stuff."




On Mon, Jan 31, 2022 at 12:26 PM Allan Hesch <allanhesch at gmail.com> wrote:

> Hello all, I'm very out of my depth here so I'm asking for any information
> at all.
> An off-grid friend in New Mexico is building a conversion which will use
> 144 volts, maybe 25-30 kwh, of Lifepo batteries and an Orion BMS 2. He's
> wanting to use enough panels in series and a suitable charge controller to
> charge the truck. No ac charger. This makes sense to me except that I don't
> know a dang thing about it!
> Assuming plenty of sun, a charge controller that puts out steady regulated
> voltage (varies the amperage as the sun's output changes) and no daily
> commute, what are the drawbacks here?
> Some concerns:
> How will the Orion deal with often variable amp input and probable
> occasional low or no voltage? Damage? Ability to balance even though amps
> of input current will change? Interruptibility?
> How will the batteries deal with a DC input which is sometimes higher and
> sometimes lower amp and doesn't taper when it should?
> Anybody know of a programmable solar controller that would be up to this
> job, say 165-170 volts? He has a line on one but is looking for suggestions
> as well.
> I'm thinking plenty of people must have done this, maybe there's even a
> facebook group.
> Any ideas, suggestions of even spitballing would be much appreciated!
> Allan
>
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