The combination of an increase in weight in an EV coupled with the lack of the plentiful vacuum that ICE provide means that in most cases some efforts must be taken to upgrade the brakes (this may even be required to register your vehicle). There are several options but the stopping power of your new EV should be as effective or better than the old car to maintain the safety of you and the car you have spent so much time and effort building. Below are possible options for upgrading your EV's brakes:

• Install a Vacuum Pump: If your donor car had power assisted brakes then this is generally considered a must for your conversion. This process involves buying a small 12V vacuum pump and a reservoir (either a tank or some use PVC tubing) to connect to the existing power braking system. Sometimes some noise dampening may be desirable as the pumps tend to make a lot of noise.

• Increase the diameter of your brake rotors: Every inch of rotor diameter increases the brakes leverage to stop the vehicle. Many models of car/truck have larger brake discs available for sporting models. For some more pedestrian models look to bigger cars/trucks from the same manufacture. For example the Chevy s-10 has rather small rotors. I noticed while walking through the wrecking yard that the Chevy Astro van has big rotors, that appear to be able to be made to fit.
• Install a smaller master cylinder: This obviously has limits to how far you can go, but a small change in the bore of the master cylinder will increase the power at the brakes, while using the same pedal effort (with a proportional increase in pedal travel)
• Install stainless steel braided brake lines: These will not increase the power of the brakes, but they will reduce excess pedal travel, by not expanding with the pressure of pressing on the brake. This can help reduce excess pedal travel from the install of the smaller master cylinder.
• Buy high performance brake pads: High performance brake pads can have significantly more friction. This can be quite dramatic, although it comes at the expense of brake longevity, a small price to pay, in my opinion. (Buy performance street pads, and not racing pads. Pads designed for track use require being "up to temperature" before developing full stopping power.
• Install a Hydrobooster: Hydrobooster is like a vacuum booster except it uses your power steering pump to provide power, instead of a vacuum source. You can find these on most 3/4ton and 1 ton trucks. Best/Cheapest place to locate them is in a junkyard. If you get one from a junk yard, you need to get the power steering pump with it as well, as it is a bigger pump and you will need the extra fluid flow to power your brakes. Some adjustment of pedal throw or master cylinder bore size may be needed after installing one of these.
• Vent Brakes: Venting brakes is a trick used by street rodders to increase braking capacity. Drilling holes in surface areas of Drums/Rotors where Pads/Shoes contact. This allows the gasses and pressures of brake dust and heat to easilly escape the mating surfaces, increasing the contact area thus better braking performance. with a 1/4 inch drill bit, Drill three to five holes diagonally across the contact surface of the Drum/Rotor. This should be repeated four times in a version of a clock face 12, 3, 6, and 9 O'clock positions. YOU MUST TURN DISKS/DRUMS AFTER DRILLING. This is to remove any burrs left from drilling. Best scenario is to start with new Disks/Drums. Venting brakes is easy to do and will increase braking ability by aproximately 25%. You will notice it immedeately. For many vehicles, you can also purchase cross drilled rotors from any number of parts suppliers (or try ebay).