How to make Total based shipping ignore some products ?

Hello,

I using extension "total based shipping" which calculate delivery price based on total price (more you buy, cheaper delivery you get). This is ok, but there are few products (in one special category) which should be ignored by this calculation. Simply, products from one category should not affect delivery price in any way.
For example:
Category 1 - delivery is calculated for this category, product - price 10$
Category 2 - delivery is NOT calculated for this category, product - price 5$
If you buy 2x product from category 1 AND 2x product from category 2, you will pay: 2x10 + 2x5 = 30$, but price for delivery will be calcullated only from 2x10 (2x product from category 1) = 20$

Any Idea how to do this ?

I am using opencart 1.5.3.1 and have minimum knowledge of it (started about 2 weeks ago).

Is this my Total-Based Shipping extension? If so, if you want different rates for different categories you'll need to get Category & Product-Based Shipping instead. It adds Product/Category/Manufacturer/Product Group rules you can use to set different charges for different products, then combine them together using a Charge Combination.

If it's not my extension, you'll need to contact the author of the extension to see if they'll add that kind of functionality for you. Given that it's quite complex to add, they may not be willing to do it for free, but you'd need to ask them.

Another option might be to set the products that do not require shipping to "Requires Shipping: No". That way they should not affect any shipping calculations (if your shipping extension is coded right). The only downside to that is that when purchased by themselves, the customer wouldn't be asked for a shipping address.