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diy solar

LFP for EV's projected to be less than $56 per kWh within 6 months

silverstone said:
Power = Torque x RPM

So ... it depends. Also if you use a gearbox or not (typically for hybrids you might have one, for pure EV ... I don't think it makes sense).

Not every EV is crazy Torque like Tesla eh. Less torque = typically less current. And less insurance premium.
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My elementary rationale to this is electric dirt bikes
Mototec for example uses 24v for 500w bikes, 36v for 1000w, 48v for 1600w, and their 72v machine has a 5000w motor.
There’s numerous comments saying ev don’t use 48v so I guess my corollary is because of the instant demand makes it less sensical?
 
G00SE said:
My elementary rationale to this is electric dirt bikes
Mototec for example uses 24v for 500w bikes, 36v for 1000w, 48v for 1600w, and their 72v machine has a 5000w motor.
There’s numerous comments saying ev don’t use 48v so I guess my corollary is because of the instant demand makes it less sensical?
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It also depends how the motor speed vs voltage characteristic is.

It depends if your target is "high torque" i.e. current i.e. dI/dt (i.e. voltage), or "high speed" ( which depends how many "volts" it takes to your motor to achieve a certain "rpm").

Everything can be done. Buck-boost converters, isolated high-frequency soft-switching transformers, etc. But it also takes space, cost, weight, etc.

If it's a mains powered or charged device, your "charger" is actually just a 400 VAC supply typically. With some rectifier / Active Frontend, you are just close enough to the target (battery and DC-link) voltage, without huge voltage transformation ratios (duty cycle). I agree with @mciholas on that side at least.
 
It's hard to compare EV voltage with stationary voltage and large comercial/industrial voltage. All of these operates at different levels.
EVs don't follow the same rules as the other two.
This comes down to economy of scale. The more you produce the cheaper it is to produce. Will we see higher voltage, maybe but only if someone thinks it's going to make a bazillion $$$!
 
The main reason for the 48V for home systems is safety and the regulations around it. Anything under 60V is/was considered safe within most legislations, and coming from a lead-acid world, this made sense since you could put 4 batteries in series and not exceed this voltage - thus no special requirements were needed on equipment, installations, etc. Anything over 60V is more problematic, and since these systems started in the DIY and especially the Marine environment (Victron comes from there), it's stuck around.
 
By the way, the current Low Voltage Directive in the EU for example sets the DC limits from 75VDC to 1500VDC - so anything under 75VDC does not need to worry about complying with the LVD.

single-market-economy.ec.europa.eu

Low Voltage Directive (LVD)

About the directive, implementation and guidance, standardisation, and contact points.
single-market-economy.ec.europa.eu single-market-economy.ec.europa.eu
 
upnorthandpersonal said:
By the way, the current Low Voltage Directive in the EU for example sets the DC limits from 75VDC to 1500VDC - so anything under 75VDC does not need to worry about complying with the LVD.

single-market-economy.ec.europa.eu

Low Voltage Directive (LVD)

About the directive, implementation and guidance, standardisation, and contact points.
single-market-economy.ec.europa.eu single-market-economy.ec.europa.eu
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Well from an (all-in-one) inverter standpoint I'm not sure it changes a lot. You have anyway 230/400 VAC in there, potentially much more from PV (1000 VDC).

For Battery, BMS, Charge Controller / Battery Charger though I guess it makes the certification easier (y) .
 
silverstone said:
Power = Torque x RPM

So ... it depends. Also if you use a gearbox or not (typically for hybrids you might have one, for pure EV ... I don't think it makes sense).
Click to expand...

With only one motor you have to have a differential of some sort. Mine both have a "reduction gear", though not a shifting gear box. Since electric motors have linear power curves, shifting gears is pointless.
 
silverstone said:
Well from an (all-in-one) inverter standpoint I'm not sure it changes a lot. You have anyway 230/400 VAC in there, potentially much more from PV (1000 VDC).
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Because back in the day, all-in-one didn't exist, and wiring up the inverter would need an electrician - who very likely was not certified for DC systems, let alone higher voltage ones complying with the LVD. A lot of all-in-ones sold in the EU don't comply with the directive in the first place.
 
upnorthandpersonal said:
Because back in the day, all-in-one didn't exist, and wiring up the inverter would need an electrician - who very likely was not certified for DC systems, let alone higher voltage ones complying with the LVD. A lot of all-in-ones sold in the EU don't comply with the directive in the first place.
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Well they need to comply on the AC and PV side. Or you think it's yet another case of manufacturers thinking "if they don't find out, it's not cheating" ?
 
silverstone said:
Well they need to comply on the AC and PV side. Or you think it's yet another case of manufacturers thinking "if they don't find out, it's not cheating" ?
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Victron complies, but they only have to worry about the DC side on the charge controllers and the AC side in the inverter. Both are pretty trivial, but it still requires independent testing and verification - can't be self-assessed. I don't think any of the popular all-in-ones like those MPP Solar ones comply.
 
ksmithaz1 said:
With only one motor you have to have a differential of some sort. Mine both have a "reduction gear", though not a shifting gear box. Since electric motors have linear power curves, shifting gears is pointless.
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Not pointless, just you may be OK with constant torque, constant thrust, same at low speed as at high. That is to say, horsepower linear with speed.
That could work for typical car use.

If you use 100 HP driving into the wind at 100 mph, are you OK only having 10 HP carrying a load uphill at 10 mph?

A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)
 
Hedges said:
Not pointless, just you may be OK with constant torque, constant thrust, same at low speed as at high. That is to say, horsepower linear with speed.
That could work for typical car use.

If you use 100 HP driving into the wind at 100 mph, are you OK only having 10 HP carrying a load uphill at 10 mph?

A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)
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@ksmithaz1, @Hedges: my point was on high-level. Whether you have 1, 2 or 4 motors it doesn't really matter. Differential (in order to be able to turn) is for sure a thing, but in the grand scheme of things the law I illustrated above holds.

On the mechanical side:
Torque ~ Acceleration
Rotation Speed ~ Driving Speed (assuming no gearbox)
Mechanical Power = Torque x Rotation Speed

And on the electrical side for a 3ph motor:
Torque ~ Current
Rotation Speed ~ Voltage
Electrical Power = 3 x Phase-Neutral Voltage x Phase Current x cos(phi(current,voltage))

(plus plenty of other things, losses due to cooling, R x I^2 and other stuff of course)
 
Hedges said:
A 2-speed transmission would let you have much higher pulling power in low gear.
(even some winches are 2-speed.)
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Sure, but in the EV world, I'm so glad the Tesla Plaid had prove that single gear ratio work fine.
0-60 mph (0-96 km/h) in 2 seconds and 217 mph (350 km/h) top speed with single speed gearbox (y)
 
In other words, with a 1000 hp motor and big enough battery, it can be geared for 217 mph top speed and still have phenomenal acceleration from a standing start.

To make that economical let's consider 50 hp and half the top speed. 1/10th the acceleration, 20 seconds zero to 60.
Ok, 100 hp a more acceptable 10 seconds.

But with a 2-speed 3:1 transmission, better towing and low speed hill climbing.

The question is, which costs more:

Second pair of engaged gears and a clutch mechanism, or
More powerful motor and circuitry to support 3x the current.

It may be that a 2-speed motor with switchable windings could be the solution, but I don't think so. Needs stronger magnetic attraction to trade off lower RPM.

The original roadster had 2-speed transmission but kept blowing it up. Seems like either two much power or motor not synchronizing speed when shifting.
 
Hedges said:
In other words, with a 1000 hp motor and big enough battery, it can be geared for 217 mph top speed and still have phenomenal acceleration from a standing start.
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The thing is peoples want EV with big range who imply big battery.
With big battery, high peak power is almost free.
That why many EV have outrageous peak power number and are the most powerful vehicle in their category. (sedan, pick-up, SUV etc).
 
silverstone said:
EDIT: yes, the equivalent for "same losses" would have been 10 mOhm vs 10 x (10)^2 mOhms = 1000 mOhms. At least for conduction losses in BMS. For switching losses is more complicated than that (in Inverter), as theoretically it's a linear relationship, but in practice higher voltage MOSFETs are slower (except SiC) and have higher Qrr (reverse diode recovery), plus Gate Capacitances and the whole drive circuit also.

However, you are a bit comparing apples to oranges here.

If you want to TRANSFER the same amount of power at 10x higher voltage, you will have 10x more current.
If you want the SAME POWER DISSIPATION at 1/10x of the current, you will need 100x higher resistance, agreed.

Can you get a MOSFET with lower resistance ? Of course. Just pick one where the MOSFET channel width is larger, or parallel several of them. For a BMS that doesn't really matter, but for an inverter that will significantly increase switching losses. Again, everything it's a compromise. Of course you can do ZVS (Zero Voltage Switching) or ZCS (Zero Current Switching) i.e. Soft Switching to reduce Losses, but that requires extra components (capacitors, inductors), more complex control topology, measurements, etc.

But the FET you linked is 5 $ / PIECE vs 0.5 $ / PIECE of the 2 comparable that I linked (at small quantities, similar discussion can be had at higher quantities). And for the battery-side of the inverter in the best case you'll need 2 (without isolation transformer, without paralleling) or 4 (full bridge, with isolation transformer, without paralleling). Then if you start paralleling (due to steady-state current, loss reduction, cooling more compact, etc), you might end up having to use 8, 16, 32, 64 etc of those ... The cost adds up.
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silverstone said:
That's also what I was saying with the "Battery Module" idea of 16s-32s each.

About the FETs ... Well, if resistance vs blocking voltage was linear, yeah ... Not much linear with semiconductor devices.

Quick comparison: 60V, ~40A, 10mOhm
https://www.digikey.dk/en/products/filter/transistors/fets-mosfets/single-fets-mosfets/278?s=N4IgjCBcoGwAwA4qgMZQGYEMA2BnApgDQgD2UA2iAKxwDsCMMIxATAMy21UAszI7nbmz604bAJxwIxbtyoxxVPuwTja4kS3pUlrbnBhtd-CWt56w8JsRphuDZd0tg4jy3HP8nccda8u1Pll5X0cWJ2NwsAQ2YT02GCoNeMTPcPsEFkd4Flc9GBjpEFoYdSoi8IK2LJkqBCkarxKxZXkYaNbGXKCEBG9WqgSiuXrw1pi2NKTucSm%2B3uV4KhYK9qdPGCdNxpYYLVVFrXFVjkDWTZokc%2BWwHcYwHmVaIav%2BZ-bk4oKHvLfuC6eg1oOy4HDibyBaRKuWMwVi4K031oT20ry02k%2B6IYv32tFkT3Ekwq9TEfhY9T2yNYCFE7WUNIMOwZdXpklurKkkVU8gR3KSyjZkwFYGimOO0VhdWeOPEuRarFllwFbBFkUJjDR4kUkgF2uGNJKCK1Ur4bDgHkQpvNhNeZrsZqt0T2VpY5V%2BZtdBitbBixjNQh9fAKNE%2BwZcQYQNF%2BtI8Ige8Dj6iKwLg-OIwJ9fk4u2TwMMQa1hKpxT6NBEvnZxBi9GL1YWVY4ByrNG4xYUrdbfGxdj4klJvYeJQHs0asx4nkUM2Mil6RRc5tdfHncF2S-NUleLionGLLj2luIe%2BDa4KCDndB8nxFqc4S639CDW2qd8vxhFIqcd7sdMPH8ev9kQNiE2SxYjvewVTvS4-BFM9w1-XowMPfQWC0JcUPJdCVxYK8UIdZCV0ggjULnJwHlwh52HQ3IVnQ7cuHQwQ-BAwxjBKHh8PAexW13Ght1%2BB5YjkJceAMIoWKA4pdneJd4BVTxgTAbNZPYeVwEMAxfnsThGBEIZK3Uy5PhoehNlk2lPGiFYvUPTIXFebS8V3SM5DY-Z-xABQrDnRRnk3cQYlKR9LCECN-nqZQOC4ZNtITVgosGEAAF1iAABwAFygEAAGV0oAJwASwAOwAcxAABfVgDCQaAQDQSAsDwIhSAoTy4AAAgANSDKguojPr0w67r0164aQHqPqUpADKsoAVSKgr0oAeXQABZfBMFwABXPL8Aq4gAFoslq%2Br8q25qyEgSglCS8rKs85AQAKgATLKDpcIoZsgEA%2BHSgBPVK9u%2Bza0DuoA

Quick comparison: 600V, 10-12A, 280mOhm-750mOhm

Cost can be considered similar.

But the higher voltage will result in ~1x-3x MORE losses.

Please note that this was just a quick search, by no means exhaustive :) .
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"Sweet spot" for mosfets or bulk dc-rail capacitor is currently somewhere around 400 volts. Superjunction mosfets totally changed the game and SIC is pushing the performance even further.

And 60v mosfet would be usable only for maximum 24v system unless you like to design your inverter for even less margin than Chinese do.
For 48V nominal system(max 60v input) 100v would be reasonable minimum, leaving 40v margin.
48v nominal 5kV inverter would need say 10x 100v 10mOhm mosfets in parallel for 10W conduction losses. Total gate charge to drive would be around 400 nC.
400V nominal system would handle the same power with single IPP60R065S with a total gate charge to drive only 51 nC. And it cost less than 10x low voltage mosfets.

On 400V system you have 10x lower part count, fraction of gate charge to drive, WAY simpler layout when you don't need to worry about paralleing 10x high current switches and lower component cost.

Like stated earlier, if 48v would make sense the electric cars would use it. Voltage required by motor is not any relevant argument, all EV motors are custom built and if it would make sense they would be wound for 48v system.
 
On EV voltage topic I have to admit that there was at least one "half-witted" low voltage hypercar project here in Finland.
Toroidion 1MW, 1300HP hypercar that was supposed to operate at low voltage to improve electrical safety.
IIRC it consisted of several motors per wheel which could be activated based on need.
 
MattiFin said:
"Sweet spot" for mosfets or bulk dc-rail capacitor is currently somewhere around 400 volts. Superjunction mosfets totally changed the game and SIC is pushing the performance even further.

And 60v mosfet would be usable only for maximum 24v system unless you like to design your inverter for even less margin than Chinese do.
For 48V nominal system(max 60v input) 100v would be reasonable minimum, leaving 40v margin.
48v nominal 5kV inverter would need say 10x 100v 10mOhm mosfets in parallel for 10W conduction losses. Total gate charge to drive would be around 400 nC.
400V nominal system would handle the same power with single IPP60R065S with a total gate charge to drive only 51 nC. And it cost less than 10x low voltage mosfets.

On 400V system you have 10x lower part count, fraction of gate charge to drive, WAY simpler layout when you don't need to worry about paralleing 10x high current switches and lower component cost.

Like stated earlier, if 48v would make sense the electric cars would use it. Voltage required by motor is not any relevant argument, all EV motors are custom built and if it would make sense they would be wound for 48v system.
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Well, the higher the voltage at 75kW+ motor output, the smaller the motors need to be. Winding size would be dramatically reduced at higher voltage.
 
Supervstech said:
Well, the higher the voltage at 75kW+ motor output, the smaller the motors need to be. Winding size would be dramatically reduced at higher voltage.
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Voltage makes no difference in motor size or winding size, just wire gauge and number of required turns.
Practical limit for lowest reasonable voltage would be 1-turn winding.
 
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