Newbie with questions

Hi all…

I am new to the idea of building an ev and am therefore over run with questions.

I am a fabricator/mechanic, but don’t know enough about DC to get this thing plan going.

My first question…is it better to have a high amp/low voltage battery, or high voltage/low amp pack?

it seems to mee that you would be better off with shitpot full of voltage that you could then step down. there would be a loss, but wouldn’t you be able to make use of the bottom half of your charge if you did so?

secondly…why DC rather than AC

I’ll tackle this one a little… First off, what kind of vehicle? I am converting a bike.

Well. The voltage current thing depends on what you want really. Its not whats better, its what is most efficient. If you want to have 144V, you need 12 12V batteries. If you have 18Ah 12V bats, and they’re 13lbs (like I do), then its a 156lb 144V 18Ah pack… and you can run smaller wire (lower current, higher voltage, less loss).

If you have a lower voltage pack, say, 72, with 6 50Ah batteries, it might be 300lbs., you will get more current, but the current carry capacity of the motor and wire will need to be greater. PLus the added weight.

Higher voltage sometimes means higher cost components for the controller and motor. Lower voltage is often cheaper. Cost is another concern.

So, depending on the controller, you can actually PWM a 144V pack to 72V and get more current output…

STart looking at prices of controllers… they start increasing in price a TON after 72V.

as far as reasons for AC vs DC, COST COST COST. AC is expensive because it requires more components on the controller and more brains. the motors can be cheaper than DC. AC requires less maintenance, while DC has more (because of brushes). AC has regen, DC you need a special controller. AC has 3 wire for carrying current, DC has 2 and may require higher gauge wire.

High-ya Newbie, First of all, AC is slightly more efficient, and can spin faster, so it is more suitable for direct drive (no transmission), but it is lots more money, 2-3 times. Part of the reason is that AC usually runs at higher voltage, an inverter is required to supply the AC.
DC is cheap, and simple. DC produces loads of torque, and DC is commonly used in commercial equipment, so parts can often be sourced from forklifts, ETC.

As for high voltage vs. high amps, It really depends what you are trying to do. Do you want to go far, or do you want to go fast. If you want both, you will need both High volts, and amps.
I’m no expert myself, but I hope this will help. If I read you right, regarding using the bottom half of your charge. This should be avoided. Batteries are pretty much all designed to run between at a set voltage, and to run above, or below dramatically reduces the life of the battery. To get down to 10v with a 12v battery is really pushing that battery, and is doing damage. Every battery is different, but most will have their life shortened in direct relation to how far they are discharged. A typical driver of an EV will try to never exceed 80% discharge (about 11.5 volts, for a 12v battery)

Generally it is best to have the highest voltage pack you can. This gives higher speed, and some increase in efficiency.
Pulling a lot of amps, will heat your motor, and decrease your range dramatically. If you plan to go very far, it is imperative that amps used be kept to a minimum. The slower the motor speed, generally the higher the amps that are drawn, and the hottoer the motor gets.
On the other hand, having a lot of amps in the battery pack (amp hours) Is always good. You will almost always want as many amp hours as you can afford, and can stand, as far as weight goes. Generally the more AH’s the more weight. The more amps you use the shorter the distance you can go. The more amps you have stored, the further distance you have the potential to travel
Think of it like this Volts= speed, Amps= distance
Hope this helps, Hell I just hope it makes sense (I’m awfull tired) Eric

Dammit I type slow! I spent so long coming up with a response, frodus already had one up, before I was done. Very well said frodus, If I say so myself

haha, I was just reading yours and saying the same thing about your post…

So, To the Original Poster… I guess it depends on what you want, there are many variables… just like a car with high octane, headers, exhaust, turbo, ported and polished heads and stuff… you can pick and chose some pieces to be better and more efficient than others, but in the end, its the combination (weight, voltage, amps, RPM, regen, lipo or lead acid… etc)

my vision is to rip the ICE out of my old (92) ford ranger and then strip it of everything needed to operate the engine.

from there, i would like to stack as many batteries in the bed as the springs will allow…40 is probably where I would stop.

from there I would like to make an adapter plate that will couple the flywheel of the five speed directly to the biggest motor I can afford.

controllers and everything else will fill in the gaps.

my daily commute is only about 7 miles, so I’m not concerned with distance, but what I would really like to do is to have a portable battery pack that will be large enough to do everything my truck would need, but then also provide for my home what it would need in the event of a power outage.

would it be best to put every battery in a single string to create 500 plus volts to work with, or is it just better to max your volts out at a certain level and leave the rest for amphours.

is there a nice balance between voltage and current that would get the best of both worlds.

I will have an ac converter on board for the household thing so that is why I was thinking of an ac drive motor, but it sounds like DC might be better suited.

Now as far as charging goes, is it more practical to charge at high voltage or low voltage.

A ranger would be a good choice, I would recommend putting the batteries under the bed, in racks designed to hold them. This will lower the center of gravity quite a bit, and allow full use of the bed.
I highly recommend checking out Austin EV There are lots of truck, and every other EV you can imagine, With all the design specs, battery, controller, charger, ETC. You will get many good ideas there, and a few bad ones!!!

As for voltage, 500 is probably a bit much for anything street driven. Most trucks are in the 120-156, maybe 192volt for a pretty fast one. Keep in mind that the price of chargers, controllers,motors, ETC. goes up with voltage.
I would look around at Austin EV, and figure out the voltage that sounds good for you, then get batteries rated for the most amp hours you can carry/afford (depending on how light you need your truck to be) If you actually only go ten miles a day, you can run a higher voltage pack,144,156ish, but keep it light by getting low amp hour batteries, 40-60 amp hour. This will get you a good 20mi. but thats about all. If you want some good range, look at 150-200AH batteries, but remember AH=weight. This could be a couple thousand pounds in batteries.
Some people wire several 12v chargers in series to charge their pack, and others charge each battery individually, or you can just buy a charger set for the voltage of your pack, and call it done! Have fun, Eric

well, voltage is like speed, and current is like torque… more volts, higher RPM possible. Higher current available, more torque possible… as well as RANGE. So if you know your motor is going to spin at roughly the same speed as the original ICE, I’d max out the RPM at redline, and calculate the voltage from the torque curve datasheet on the motor.

500V is a bit much, and you’ll have to spend a LOT of money on that. Like i said, you’ll pay for higher voltage controllers.

go on and take a stroll through to see what other people are doing. Thats what I did for my motorcycle, and its proven helpful.

[QUOTE=F-N Randy;1494]

I will have an ac converter on board for the household thing so that is why I was thinking of an ac drive motor, but it sounds like DC might be better suited.

Now as far as charging goes, is it more practical to charge at high voltage or low voltage.[/QUOTE]

first off the AC drive is variable frequency, so it wouldn’t likely drive any of your houshold things, with an inverter, you’re just converting DC to AC at 60hz in america… with the controller, speed of the motor is dependant on the frequency of the drive.

As far as charging, thats a loaded question… practical comes in several forms. First, what is practical now… well, it would be to spend money on one charger, and charge all the batteries in series… which leads to what is practical in the future… you might find that charging in series without battery balancing, will unequally charge the batteries in the pack, i.e. one might not charge the same as another due to the nature of series packs. the total pack voltage might add up to 144, but one may be overcharged, another may be undercharged. So, whats easiest? one charger… whats best? likely a series charger with battery balancing… OR you could have individual chargers on each battery… in the end, do you want to spend money on 12 chargers, or 1 charger and batteries when you have to replace them, or 1 charger and battery balancing.

So the quick and easy answeres don’t exist do they?

Ok, so If I retain my original 5speed then would it be better to have a ton of torque and run the higher gears from take off, or spin at as many rpm as possible and never shift up.

I have two table saws…

one is a very expensive stationary machine that has a huge motor and drives a 10" blade directly.

the other is a portable unit that has a small motor that turns some 10,000 rpm and then the blade is belt driven down to about 4500.

Well, the later of the two out performs the first, hands down.

I’m sure there are many things to consider about the saws, but apples to apples is it better to have more rpms than more torque.