Battery boxes

[DaveH]

Battery boxes are obviously a very important part of an EV conversion, but it is almost always necessary to fabricate them from scratch, you can't just drop in an OEM battery box.

So, what are the important things to know?

• Materials: what can and can't be used?
• Construction techniques
• Mounting: how and where to mount the box, how do you know if it will be safe in a crash?
• How do you fix the battery modules?
• Does it need to be waterproof, fireproof?
• What are the requirements for safety? Contactors, insulation, grounding, fuses...
• Do you need heating or cooling? How is this done?

[jalovick]

Another thing to consider in some locations are the regulatory requirements. In Australia, a battery box needs to be handle up to 20 g impact to the vehicle.

From the Australian regulation:
2.3 Battery Restraint
The batteries that power the vehicle must be fixed in position so that they will not easily break
free in a crash and thus create a hazard to the driver, passengers or other road users. The
battery restraint system must adequately withstand at least the following crash accelerations:
Front impact – 20 g (i.e. 20 times the battery weight);
Side impact – 15 g;
Rear impact – 10 g; and
Vertical (rollover) impact – 10 g.
An impact sensing (G force) switch should be fitted to the vehicle so that the traction circuit is
opened in the event of an impact.
Battery restraints must be designed so that during fitting and maintenance operations, either the
restraints or any tools required cannot easily provide a short circuit path for the battery terminals
or other exposed wiring and connections. Similarly, it is recommended that insulated tools are
used for fitting or maintenance operations.

This may vary country to country.

[arber333]

An impact sensing (G force) switch should be fitted to the vehicle so that the traction circuit is
opened in the event of an impact.

That is easy, use original car inertial fuel pump disconnect. https://en.wikipedia.org/wiki/Inertial_switch

battery restraint system must adequately withstand at least the following crash accelerations:
Front impact – 20 g (i.e. 20 times the battery weight);

That is harder to achieve. But bear in mind front battery box is located under the hood. Steel tensile strength and a good locking mechanism can give you 10G worth of cover. Depends on the box weight. You can use the original engine mount points. They are tough since G force applies to engine block too.
This is why newer cars are designed to have the battery under the car. Also regulations dont specify connectors under fixed cover....
Now you can approximate what bolts you need to use to fasten the box to car chassis.
Yes one should definitely use bolts not welding. At least not across the chassis. That way you can introduce alternate paths for the chassis to crumble upon impact, which can cause hazard for the occupants in case of a crash.
If you have battery in the back there is less to worry about 3rd parties and more of occupant safety. All you need to do is design a clamping mechanism to keep the box in at all times.

Regarding other mechanisms i saw ECE R100s requirements.
- Bolted boxes should be grounded to chassis by at least 6mm2 line
- Also the lids should be additionally grounded
- All other parts of traction should be grounded despite heavy bolts(motor, transmission, inverter, charger, DCDC)

Boxes should be sealed with a valve to be opened (breech valve) in case of increased pressure.

I have seen inspector grabbing battery modules and giving them several unceremonious tugs.

Regarding heating/cooling... where do you live? Do you own a garage? Remember the cold does not hurt batteries directly. It is the regen and sub 0 charging that hurts the ion membranes.

[jalovick]

There are quite a few other sections for consideration in the Australian rules, including:
- Containment of Batteries
- Venting of Battery Compartments (Class B Only)
- Labelling of Battery Compartments
- Battery Management
- Allowance for Australian Climatic Conditions

There's a lot of useful stuff in there. The requirements are available here:
- https://www.infrastructure.gov.au/vehic ... an2011.pdf

Jamie

[arber333]

There are quite a few other sections for consideration in the Australian rules, including:
- Containment of Batteries
- Venting of Battery Compartments (Class B Only)
- Labelling of Battery Compartments
- Battery Management
- Allowance for Australian Climatic Conditions

There's a lot of useful stuff in there. The requirements are available here:
- https://www.infrastructure.gov.au/vehic ... an2011.pdf

Jamie

Yes, i didnt venture into those...
- Like i said physical containment was tested by hand, cover lead was inspected for seals and fasteners. Cable for grounding battery box was inspected.
- They wanted to know how i am venting the box in case of overpressure... i installed two pressure valves . They should vent under pressure and releave the box.
- I was required to put lables with energy (Wh) and Voltage (V) content on the lid
- BMS was a part of the battery. I got out easy that way. I guess i would have to provide evidence of low and high SOC points triggering

For cooling i would simply recommend you use cooling plate with coolant tubes attached under it. Maybe a tube mesh from old refrigirator condenser... .
https://en.wikipedia.org/wiki/Condenser ... 3%A1st.JPG

[P.S.Mangelsdorf]

The NEDRA/NHRA rules are also a good guide. They call for 8g horizontally and 4g vertically and also provide tables with strap and bolt requirements.

http://nedra.com/nedra_handbook.html#8_1
http://www.nhraracer.com/content/genera ... zoneid=132 Click on 2020 Rulebook, go to page 101 (linking directly doesn't seem to work)

[DaveH]

Does anyone have an opinion or any experience of these?
https://www.secondlife-evbatteries.com/ev-battery-box