Abstracts Engineering

Electric conversion of combustion engine cars

by Annika Modling

The electrification of personal transport vehicles is one of the strategies to counteract global warming and dependance on fossil fuels. Diesel powered cars are already prohibited in several big cities and the prices for fuel are constantly climbing. Even so, electric cars are still a premium that not everyone can afford as they could an older ICE-car. This means that there can be a gap in the near future were the Swedish working- and middle class can neither afford a new EV nor refuel their combustion engine car. This thesis investigates the possibilities and challenges of electric conversion of an existing, (used) combustion engine car as an alternative to buying a new electric car. The conversion is meant to be a DIY-project that can be carried out by anyone with the capacity to learn all the skills necessary and with sufficient funds to own a car in the first place. Parts of or the whole project can be outsourced to machine shops or similar, if there are areas where knowledge or equipment of the builder are insufficient. This type of conversion proves to be highly modular where the selection of both car and components depends on budget, time, and knowledge. Brushed DC motors offer reliability at a low cost, but with relatively low efficiency. A three-phase induction motor will be a more costly option, but with the benefit of higher efficiency and power. The batteries that are deemed appropriate for the conversion are lead-acid and lithium-ion batteries. Lead-acid batteries are robust and have a low cost. Their low energy density will however result in a higher weight making this type of battery best suited for a small car with short range. Lithium-ion batteries, which are used in commercial EVs, have a high energy density and lower weight. They come at a high cost however, and they require individual monitoring of the cells’ voltage to prevent potential failure. The converted car will have to be registered as a modified vehicle in order to legally be used in Sweden. The original total weight of the car cannot be exceeded during the conversion and because of this, a car with low curb weight and high max load is preferable as a starting point. Den pågående elektrifieringen av personlig transport är ett av verktygen för att uppnå en hållbar utveckling. I samband med detta stiger bränslepriser och förbud mot dieseldrivna bilar finns numera i flertalet städer. Trots detta är elbilar fortfarande mycket dyra i inköp. Elkonvertering av befintliga (begagnade) bilar kan vara både ekonomiskt och ekologiskt gynnsamt då resultatet blir en cirkulär ekonomi och minskat behov av fossila bränslen, samtidigt som bilägaren ej behöver betala för dyrt bränsle. Detta examensarbete kartlägger möjligheterna och utmaningarna kring elkonvertering av enbegagnad bil med förbränningsmotor som alternativ för att köpa en ny elektrisk bil. Konverteringen skall vara ett DIY-projekt som kan genomföras av alla som har kapaciteten att lära sig de färdigheter som krävs samt har finansiella möjlighten att äga en…