There is no statutory limit on what a landlord can charge a tenant for a security deposit in South Carolina, but it's in your best interests to set a reasonable amount. In most cases, that would be the equivalent of 1 or 2 month's rent, which is generally sufficient to cover unpaid rent and the cost of any repairs for damage caused by the tenant.
Landlords are not required to pay interest on the security deposit, nor are they required to notify the tenant as to the bank or the account in which the deposit funds are being held.
South Carolina law requires the landlord to return the security deposit within 30 days from the termination of the tenancy. If any deductions are made from the deposit for unpaid rent or damages, the landlord must also supply an itemized statement listing all the deductions.