Are there any negative consequences to consistently charging at a lower amperage than your charger’s capacity?

[HighDesertCoug]

I know that a 48a home charger is usually overkill for most EV owners – but is there anything wrong with installing one anyway and setting the vehicles battery management system to charger at a lower amperage?

The only reason I'd want 48a capability is to future proof our solution as the capacity of batteries in the future will only grow and we may need bigger capacity at some point down the road with another EV.

Other than higher installation cost, are there any negatives I'm not aware of by doing this?

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[DuoRivians]

There’s no reason to charge at a rate lower than 48amp. It won’t make your batteries last longer or reduce any degradation. The only reason to charge at a lower rate is if your wiring can’t handle it

 

[Skysurfer]

Charging at a lower rate will generally result in more losses due to the vehicle systems running longer and the power conversion system being less efficient at partial loads.

 

[JacobAZ]

To answer your question, there is no issue with stepping down from the charger's max capacity. You can set the maximum in the R1. There are valid reasons you may want to do this. For example, if your utility has a demand charge.

 

[dradam]

Even though I have a 48A charger I charge at a lower rate. I do this mainly for my home, not for the car. I have a full subpanel in my garage and even though load calcuations are ok I feel that I am less likely to over heat a wire or trip a breaker. I charge to 70% daily at 20A and the car is still topped off in the morning. In retrospect I probably would have been fine with Rivians portable charger on a 220v outlet, but is nice to have the ability to speed up charging if necessary.

 

[Nixapatfan]

No issues with charging at lower rates, no it's not going to get excessive wear on anything.

As for hardwired chargers it might be best to wait if you can. Over the next few years new bidirectional equipment is trickling out from various makes and can charge at even higher rates upto 100 amps. So if using your car battery as a generator is appealing to you then might be best to wait.

 

[electruck]

Probably not something you have to worry about in OR but here in the TX summer heat, I find I must derate to 40A in order to avoid more aggressive thermal throttling by the Rivian (if I recall, it drops down to 32A), usually within the first hour of charging.

 

[olsonchris42]

I charge at a lower rate to limit my power consumption to just my solar array and not draw from the grid.

 

[JamboF4]

I’m not entirely positive about my results, but I’ve been struggling with an overheated charge plug (hot to the touch..IR thermometer is 120 deg) it reduces its amperage. At say 36A, it SEEMS to help the overheat, but the overall charge time is still slower

 

[Zoidz]

Charging at a lower rate will generally result in more losses due to the vehicle systems running longer and the power conversion system being less efficient at partial loads.

Double sided coin: a higher charge rate inherently has more resistance losses in all of the components, from the distribution panel and the breaker, to the EVSE, cable, inverter and the vehicle battery.

Joules Law H = I² * Rt states that power loss is a function of current squared and time. Heat losses, and therefore electrical consumption and losses, increase exponentially as the charge current increases. I'm not sure if there have been any studies to compare and quantify which is optimal. Additionally, higher current/heat tends to shorten component life, so IMO there is an advantage to using a lower charge rate if speed is not a factor. I charge at 38A for that reason.

 

[ElGuano]

I think it's been pretty well covered in these answers. There's no real downside to the car to charging at a lower rate - slow trickle charging is generally better for the batteries. However, 48A @ 240v isn't very fast to begin with, and the car's on-board charger will decrease the charge rate as needed. There's little reason to lower the charging rate *for the car's sake* but potentially good reasons from a home safety/wiring/utility rate perspective.

 

[Judd]

As mentioned above, our TX garages get hot in the summer. To help with plugs, chargers, cords and wiring I turned mine down to 30a and it’s been way better on heat. I didn’t notice my truck throttling but sure noticed stuff getting hot to the touch. To the point, this winter I haven’t turned it up. Rarely do I not charge over nite, when needed, and the slower charge times has not been a factor.

 

[HighDesertCoug]

Thanks for the info all, very helpful. I think I’ll keep my plans of installing a 48a charger and then de-throttling via the vehicle.

I hadn’t thought of thermal issues but where I’m at in Oregon, we get fairly hot summers (90°-100°+ regularly) and with a southern facing garage, it gets quite hot so charging at 20-30amps on a 48a charger seems like a no brainer.

 

[carsly]

I have three Tesla Universal Wall Chargers each capable of 48 amps, but more current = more heat. Take some thermal measurements and you'll see pretty quickly that charging at 32 amps generates a lot less heat in your wiring,, at your panels/sub-panels, etc. If you're charging overnight to 70% it makes no practical difference in terms of timing even though charging at 32 amps does take longer. Me? I've opted for less heat throughout my system for safety because heat = resistance = power loss and risk of fire.

For those saying charging at 48 or 60 amps saying the vehicle wastes less power, you are 100% correct. HOWEVER the extra heat generated through your circuit(s) will cause charging losses that you're not seeing directly at the vehicle as the power is lost to heat generated in your wiring and connection points. And generally you don't want heat building up in your wiring and connection points. Short wiring runs help quite a bit here but some of us with older homes can't avoid the long runs, another argument for slower, cooler, charging.

No perfect answers, just tradeoffs. Take in account the age of your home, sizing of the wiring for high-draw over protracted periods of time, length of your wiring runs, number of panels/sub-panels in between your power source and your vehicle, etc. and figure out what's best in your situation. Charge safely and don't use cheap NEMA 14-50 outlets, or any outlets at all if you can avoid them.

 

[Golfer04]

Double sided coin: a higher charge rate inherently has more resistance losses in all of the components, from the distribution panel and the breaker, to the EVSE, cable, inverter and the vehicle battery.

Joules Law H = I² * Rt states that power loss is a function of current squared and time. Heat losses, and therefore electrical consumption and losses, increase exponentially as the charge current increases. I'm not sure if there have been any studies to compare and quantify which is optimal. Additionally, higher current/heat tends to shorten component life, so IMO there is an advantage to using a lower charge rate if speed is not a factor. I charge at 38A for that reason.

Excellent summary. I always charge at 48, but have reduced it and saw less loss; not more. When I was concerned about such matters I would drop to 36. Now I just plug in every night and whatever.

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