There is no maximum that you can contribute, however, there is a maximum that you can deduct in any one year. If you can't deduct all of your donations this year, we'll see if the remainder can be carried forward to next year. See this link for more details. Deduction limit
In general, contributions to charitable organizations may be deducted up to 60 percent of adjusted gross income computed without regard to net operating loss carrybacks. Contributions to certain private foundations, veterans organizations, fraternal societies, and cemetery organizations are limited to 30 percent adjusted gross income (computed without regard to net operating loss carrybacks), however. Tax Exempt Organization Search uses deductibility status codes to indicate these limitations.