Frequently Asked Questions

Whether you're an EV novice or expert, questions arise. We believe there are no stupid questions. When it comes to EVs and conversions, answering your questions can avoid mistakes like burning out a controller, or avoid hazards which can injure yourself or others. This is why we are committed to support and sharing as much knowledge as we can. Below you will find answers to many of the basics for any type of EV project. Topics are grouped by transportation type when applicable only to specific systems. If you can't find the answer you're looking for here, please send us an email so we can address your questions thoroughly. 

The Big Picture

  • I want to build an EV! How do I start and what do I need?

The first step in your project is take an honest inventory on your desired performance and available budget. Many people start their conversion before realizing it may cost them more than buying a used production EV. Here are some simple questions to ask:

  • How far do I need to drive between charges, and how often do I need this range?
  • What vehicle do I plan to convert? How heavy is it, and how much space and payload can it provide for batteries?
  • What speed will I drive and how often will I be climbing hills?
  • How much am I willing to spend on parts and support, including motor, batteries, machining services and installation?
  • Am I a Do-It-Yourselfer, and to what degree will I need to pay for outside help?

Study the EV conversion process by Reading DIY Manuals, joining online EV forums and talking with anyone you know who has completed a similar project. Go to The Battery University and other sites to learn about types of batteries and how much energy a battery can contain. The subject is deeper than you might think. 

After you have a general grasp of the subject, start using your performance and budget requirements to get a picture of motor and battery combinations you could use to meet your needs. Thunderstruck Motors can be a good place to go once you have narrowed your options. Use our website to help check specifications and costs for motor and battery systems we offer. 

The battery may be the most challenging part of the project. Many used battery options exist, and your research will take you down that rabbit hole! Thunderstruck Motors often has options, depending on what is in inventory. See our Batteries Page for new and used battery options.

Ironing Out Some Details

  • What size and type of battery pack will I need?

Your traction battery pack will be constructed of many single cells connected together in a way to provide the voltage and power output needed for your project. Use your starting inventory to determine power and capacity for the pack. Consider pack voltage: higher voltage means lower current and smaller wires, and it generally means higher motor RPMs. Higher voltages mean more individual cells in series - for instance, a prodution high voltage pack typically has 96 cells in series to create 400 volts. Consider "capacity" - a larger capacity battery pack allows for longer range than a similar small capacity pack. Capacity can be measured in kiloWatt Hours (kWH). Small converted cars can travel between 3 and 5 miles per kWH (level roads), depending on weight, speed and aerodynamics.

Battery cell chemistry will impact weight, power, cost and the number of cells required for a complete pack.

Motor and motor controller choice will influence your battery options, because the battery voltage and available current must match the motor/controller requirements.

  • What's the difference between connecting cells in series or parallel?

When constructing your traction pack, cells are your building blocks. Cells have a current capacity rating called Amp Hours. A 100 AH cell can provide 100 amps for an hour before being completely depleted. Cells have a maximum and minimum voltage rating. Operating outside of this range can damage the cell. 

Parallel connections are when 2 or more cell positive terminals are connected together (and the same with negative terminals). Parallel cell connections are used to increase the AH rating of a pack. For instance, two 100 AH cells connected in parallel will create an equivalent 200 AH cell - Amps add in parallel. 

Series connections are made by connecting the positive pole of one cell to the negative pole of a second cell. If two 100 AH cells are connected in series, they maintain their amp hour rating but have a higher total voltage - Volts add in series.

  • What is a Battery Management System (BMS)?

A Battery Management System (BMS) is needed for packs using lithium ion cells because they can be damaged when operated outside of a specific voltage range. Lead acid batteries are more tolerant of voltage variations, and do not need a BMS. Lithium ion packs are often used in EVs because they carry about 3x the energy per weight of a lead acid pack. A BMS performs several functions, as follows:

  • Continuously measures each cell and reports if it exceeds voltage limits
  • Monitors the active cell count and reports if cells drop out of the list
  • Monitors cell temperatures and reports if out of limits
  • Other functions are possible, including operating history and display management

Our Dilithiium BMS is a popular alternative which provides these functions - see the BMS Page for more info. 

  • How do I select my battery charger?

Your charger must match your battery voltage and chemistry. Lead acid packs can be charged to fairly standard voltages, called "nominal" - for instance, a 48v nominal pack consists of 4x12v lead acid modules. Lithium packs must be charged to specific voltages based on the cell chemistry and number of cells connected in series. Lithium packs are designed to receive a constant current to constant voltage (CCVV) charge profile so that they have a slowly decreasing charge rate near the end of the cycle. Charge controllers are are devices used to control the charge cycle so that it meets these requirements and responds to warning signals from the BMS. Our EVCC and MCU perform this function.

Chargers may plug into a standard 120 or 240 volt outlet, or may connect to special EV provision equipment like an EVSE with J1772 communication protocol. See our Charger Page for more information about available charging products.

  • How do I match my conroller to my motor?

Start by looking at our system kits pages (Sailboat, Motorcycle, AC), and you'll see that motors come with recommended controllers. When browsing motors sold separately (Motors DC and PMAC), applicable controllers are mentioned on the product page. If you are uncertain about this, then send us an email with some details about what you are considering - we will get back to you with the latest controller application and availability info.

EV Parts Descriptions

  • What is a Main Contactor?

A Main Contactor is a large electrically-activated switch (or relay) that connects the high voltage from your batteries to your controller. The controller uses a precharge circuit to charge its internal capacitors before closing the main contactor, so it is very important not to force the contactor to close just to "get it going." Doing this will skip the required prechage process. Don't make that mistake!

  • What is that pre-charge resistor and diode I see on contactor drawings?

The pre-charge resistor charges the controller capacitors slowly to prevent arcing and power surges, which can damage controllers and other components. The diode helps prevent any back EMF from reaching the controller that is caused when a contactor is opened or closed. Some controllers handle this internally.

  • Why is the voltage rating on my main contactor not the same as my battery pack or controller?

Contactors are rated for a specific Coil voltage (also called enable voltage) and their current carrying capacity.

Sevcon and Curtis AC controllers have an adjustable coil output voltage and are typically set up for 24V. In these instances, the controller is responsible for closing the contactor. Variations include the Alltrax AXE controllers, which don't have a coil output, and production EV systems like the Nissan Leaf, with contactor coils running at 12v. 

  • What is a DC-DC Converter?

These are used to step down your pack voltage down to 12 Volts in order to use a vehicles OEM lights, horn, and accessories. They typically also charge the 12v accessory battery, and have a regulated 12 Volt output. The DC-DC converter takes the place of an alternator in a  typical ICE vehicle.

  • Why do I need a controller heatsink?

A cool controller will run more efficiently, and will last longer. Short bursts of power may not overheat your controller, but if you hope to have a 100 mile range, your controller is likely to overheat without a heatsink. (You may not need a heatsink if you have a metal bulkhead you are bolting the controller to.)

  • What is an Adapter Plate?

An adapter plate helps match an electric motor to automotive transmissions. One side of the adaptor plate bolts directly to your vehicle's transmission bell housing while the other side is bolted to the electric motor through a spacer block. If using a clutch, the motor shaft may attach to the original flywheel with an adapter flange machined for a perfect match. After correct installation, the motor and transmission are positioned exactly as the original manufactured equipment. Thunderstruck Motors can provide support for some VW installations, but numerous options can be found by running an internet search for an EV adapter plate designed for your specific vehicle model.

  • Why do I need a display?

A display will allow you to see essential information for safely operating your system. Information like pack voltage,current, motor RPM and temperature can be invaluable and  enhance your enjoyment by increasing your understanding and confidence in the system. The more you know about your electric system, the better able you are to respond to it for increased safety and longer life. Understanding EV operating data can also make communication with other EV enthusiasts more enjoyable and informative. See our Instrumentation Page for some display options we support.

  • How do I determine correct gear ratio for an electric motor?

Check out our Gear Ratio Calculator for a simple tool allowing you to experiment with different ratios. This can be useful when working with a chain or belt drive system like in a motorcycle or boat.

  • Do I need to program my controller?

The Curtis AC and Sevcon Gen4 kits are sold as full functioning units. We will use the information you provide with your order to configure your controller, and will bench test it after configuration.

If you find the need to adjust settings in your Curtis or Sevcon controller after installation, some programming tool options exist for rental or purchase - see our Programmers Page.

For all controllers, please visit the Controller Page for links to information covering each device.

  • How do I know which throttle to use?

Motor controllers can handle various throttle options. See the Throttles Page for options we offer, and specific controller or system kit pages will give options for throttles available for your controller. Different throttle types may require custom programming, so decisions about throttle should be made before ordering your system. Here are some general throttle capabilities to consider:

  • FNR (Forward Neutral Reverse) capability, typically for marine applications
  • Cable to control arm attachment for existing remote throttle installations
  • Twist-grip or thumb activated, typcially used with motorcycles or off-road vehicles
  • Foot activated throttles, typically used for 4-wheel land vehicles
  • Hall-effect (magnetic) or potentiometer (resistive "pot") type throttles

Send us an email or call us if you don't find the info you need to make your decision.

Sailboat Systems

  • Which sailboat kit is best for my sailboat?

There are many variables that affect performance while sailing with electric installations - boat displacement, current, wind, motor power and RPM, battery capacity and prop specs are all part of the equation. Start by looking through the different systems on the Sailboat Kits and Accessories Page. Each kit page provides information about how to match the kit to your boat, based mainly on displacement. 

Here are a few things to consider when planning your conversion:

  • Consider using half "hull speed" when motoring with electric. Higher speeds cut considerably into duration estimates.
  • Onboard generators can extend range by creating a "hybrid" system. This can be useful for day sailers wanting occasional extended range.
  • Consider looking through some online forums like Electric Seas.

If you need help making this decision, please don't hesitate to email us with your boat specifications and the systems you are considering. We will do our best to reply quickly with suggestions. 

  • How do you provide such a low price for your kits?

We use the same motor and controller as some of our competition. We make our own gear reduction in-house which allows us to keep costs low and quality high. Additionally, our gear reduction is optional. Most other companies include the gear reduction in the price of their kits. Also note that our kits are not a drop-in box. The customer is responsible for installation, mounting and alignment. This allows us to keep prices affordable and makes the kits more versatile for the large variety of boats out there.

  • What else do I need in addition to a sailboat kit to get me out of the docks and into the water?

We bench test the controller and harness of all the sailboat kits we sell to confirm that it's set up according to your needs. You'll need to get batteries and a charger. You will also need power cables for connecting your batteries, and some way to hold your batteries in place.

Purchasing a heatsink for the controller is a good idea, but not always necessary. A heatsink may impact how you mount your controller. Having air circulate through the engine compartment is beneficial, and may be necessary. If installing a liquid cooled system then a pump, radiator or heat exchanger will be needed.

How you mount your motor depends on whether or not you install one of our gear reductions. If you decide not to use a gear reduction, you'll need a thrust bearing in line with the prop shaft because most motors are not rated for axial/thrust loads. The gear reduction includes a thrust bearing, and comes with a coupler for connecting to your prop shaft.

When ordering your kit, you will be asked for information about your boat, battery pack and throttle choice. Please email us with your boat information if you need verification before ordering. 

Working with Thunderstruck Motors

  • Why should I buy from Thunderstruck Motors?

Find out what ThunderStruck Motors offers Here!

  • What if I lose the manual to one of my components?

See our Manuals and Data Sheets for information about EV products we have offered over the years.

  • Can I return something I purchase if I don't like it?

We want you to be satisfied with your purchase and most items are returnable if undamaged.  For quality and safety reasons, some items such as batteries are not returnable.  See our Return Policy for more information.

  • Help! I don't understand electrical theory!

Check out Battery Univeristy or our Understanding EVs page. See DIYelectriccar for others who may have converted a similar vehicle. You may also find this FAQ by Plugin America or The Endless Sphere forum helpful. Check them out!

  • I want to see more photos and videos of all of the great things you guys are doing!

That's great! We try to showcase neat things we do and share what others in the industry are doing via our social networks. Check them out below! By adding us on Google+, Liking us on Facebook, Following us on Twitter or Subscribing to our YouTube Channel, you will be kept up to date on all our latest mischief.

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  • Haven't found the answer to your question here? Ask us your question in the comments section below and we will do our best to answer it for you. Detailed questions are best submitted via email.


What motor would you recommend to convert a Boom trike to EV? I was looking at the Mustang Family as the available space can take more battery packs.
That looks like a good candidate for the AC-35 family of motors. What is your budget?
CAn I use a pot 0- 2k ohms on a controller gen 4 size 2

tanks in advance
Best regard

Yes you can, although the controller will have to be programmed to function with that input.
I would appreciate further information about the kart kit with Fwd/Rev and regen 15kW.
Is the voltage fixed or can it be ordered with any voltage (i.e. 24V)?
Regarding the delivery, are AGM batteries shipped to Europe?

Hello Juanjo,
The controller is operable from a 24-48V battery input. If you order the kit, we can program the controller for a specific voltage. We recommend sourcing lead acid batteries locally simply because they are heavy and costly to ship.

When starting a new project and considering ac or dc motors what should govern my decision.

The DC motors that we stock tend to be more simple and cost effective for smaller, or lower power projects. The AC induction kits we sell cost a bit more, but tend to be rated for higher power or for larger vehicles. There's no reason you can't use an AC drive in a smaller vehicle if there is space for it, and it's within your budget. If you want to fine tune the drive characteristics, consider a very simple DC controller like the Alltrax, or the highly flexible AC drives with Curtis controllers. -TSM
Gear reduction....all your data seems to be from diesel motors I have an Atomic 4 and need some info on if I need it.. Do you have any history for converting an Atomic 4 to Electric? Motor is out and Im ready to go once I have all the data

Absolutely you can convert a boat with an Atomic 4, in fact it's probably the most common engine to be replaced with an electric drive. Give us a call or email and we'll try to answer any other questions you have. -TSM
I have a house boat that we had to remove the motors on. I was impressed by your video on the sailboat motor.

The boat has a ton of room for batteries so it seems like it would be a good application to convert the boat to electric.
the boat only needs to got 5 MPH or max10. it is light . and has lots of room for solar panels and generator.

I would love to know what you have that would fit this application.

Hey Scott, what size engines were on it originally. We could find a motors with similar power outputs for you. -TSM
Hi there, I was told if I unhook my speed controller, my golf cart would go faster. Any input on this would be a great help!

I don't know what kind of motor and controller you have, but without the speed controller, hooking the motor directly to the battery is both dangerous and difficult to regulate motor rpm. This might be funny on an rc car but it's a bad idea on something this big. It may be possible to tune your controller for higher output though. -TSM
I am thinking about converting a simplicity 3316h hydrostatic tractor. I am thinking I can control rpms by battery voltage but I look to you for your knowledge. What would I need to make this garden tractor run well? I'm not too concerned about efficiency as I will add more batteries as needed. I plan on 4 group 31 bAtteries on the tractor and 4 more on a trailer or roller I will be pulling as I mow. Mowing with a 50" deck and snow blowing are going to be the main chores for what I use this tractor for. Let me know your suggestions and thoughts please. Thank you very much

Hi Darryl! The safest and most efficient way to vary the motor rpm is through a speed controller. This allows for a slow start with no giant sparks at your switches. Do you already have a motor picked out?
In your FAQ you say: If you decide not to employ a gear reduction, you'll need a thrust bearing somewhere in line with the prop shaft because most motors are not rated for axial/thrust loads on the shaft.
Can you please explain axial/thrust loads on the shaft.
I am planning to order 2800 RPM at 48v, (AC-20 w/1238-5601 if I use gear reduction, my RPM drops a lot. So please advise.
I have a 15ton sail boat.
Also interested in shipping costs to 'Belize, Central America.A
Thanks, Gale P

Hi Gale! That's an excellent question. The thrust bearing is to protect the motor from the forces of the prop. Imagine that the propeller is pushing the boat, so all of that forces to move the boat is pushing on the end of the motor. Most motors are designed around having a chain or belt on them, which has a different force, one that pulls sideways on the motor shaft, not directly into it. What kind of boat do you have? We are releasing a new stainless steel AC motor that is manufactured specifically for the marine industry. -Michael
Planning to install a Sevcon Brushless Sailboat Kit - 10.5KW with the TS Gear Reduction and would appreciate for my final plans the dimensions, specially of the gear reduction system.


Hi Carlos! We have dimensions of the motor and controller on our specs page found here:
The reduction plate is approximately 8"x13" with a shaft that is almost 10" from the plate. -TSM
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