backchannel: clarifying some points in clueful comments

A clueful commenter provided good info in a newbie’s thread about a (poorly) pre-built van power setup.

I’ll address a few points here rather than in the thread as they are minor.

One solar panel. Maybe 100 Watt rating. Could be less. If old, may not be that efficient.

Panel efficiency isn’t really an issue here. It’s a single panel in a spot that could hold more.

this could generate about 500 Watt-hours

OP appears to be in Europe, based on the 240v plugs. Getting 500Wh/day is highly unlikely. It would require >7 hours of Full Sun Equivalent, even if the PWM weren’t hamstrung by bank voltage.

One 85 Ah flooded lead acid battery. Lead acid can only be discharged to 50%

True, but the main issue is that it’s not a deep cycle battery.

A Solar Charge Controller. This takes energy from the solar panel, converts it to the proper volts to charge your 85 Ah battery,

PWM controllers don’t do any voltage conversion.

My main problem with the controller is the output is going to the fuse box rather than to the battery bank. Voltage sag will further hamstring the already-feeble solar charging.

Recommended:

1. solar charge controller -> battery bank
2. battery bank -> 12v fuse bod

and manages the charging properly.

Depends on what properly means. It’s a single stage charger, so we basically get to pick an Absorption voltage (Vabs). In this case that’s almost certainly fine because the battery will probably not reach Vabs anyhow.

This is a “Pulse Wave Modulation” charge controller, which is an older, less efficient, less robust technology.

Older, yes. I’d argue it’s more robust (less to break) and more efficient (power in == power out). MPPT typically have ~5% DC-DC conversion losses. There are edge cases where PWM will outperform MPPT.¹

I’d say MPPT usually results in greater overall harvest, but does so less efficiently and at greater capital cost.

A Cargo split relay… I also don’t know how your van’s alternator is charging your 85 Ah battery - looks like there is no real charge controller, so it may be basically treating it like a second van battery.

Yes, the starter battery and house bank are effectively paralleled when the VSR is active.

Check your Ecoflow for how it can be charged by your van alternator.

[in this section the commenter is, correctly IMO, encouraging OP to delete the house bank and use a power station they already own]

A simple plug to the cigarette lighter will generally get you 10A at 12V which is 120 Watts per hour the van is driving.

120W x 1 hour = 120 Watt-hours, not “watts per hour”. A common misunderstanding.

That is not a lot. If you need more, invest in a small DC-DC converter to pull higher amps into your Ecoflow. Check the specs on your Ecoflow and google around to fine what others have done for your exact model.

Since they deleting the house battery, it might be cheaper to buy a MSW inverter to run behind the VSR and use the Eco’s wall charger. Eco does make a DC-DC charger but it’s probably overkill for their “600w” power station. I might consider the Etaker at half the cost; it’s better matched to the bank Wh and has an MPPT controller built in. I know the Eco has MPPT but on smaller power stations there is typically only one DC input. The Etaker would feed that single input, if that’s the case, from both sources. Otherwise OP might have to manually plug in solar or alternator charging, whichever is active.

DC-DC chargers for power stations.

1. OP’s case is not one of them. ↩