There is no maximum but,

If you donate a single item or group of similar items with a value of more than $5000, you must have an appraisal signed by a qualified appraiser, who also signs a copy of form 8283, and form 8283 also has to be signed by a responsible financial official of the charity.  You are also required to have documentation in sufficient detail to allow you to determine the fair market value -- this minimally includes how you acquired the item, the amount you (or your mother) paid for it, and the condition at the time of donation.

There is very little guidance on what constitutes a "group of similar items."  For example, can you split up household goods into one group of furniture, and another group of kitchen goods, and another group of linens, and another group of clothing, or should it all be one group.  It is not clear from the instructions how thin you can slice the salami and not get called on it.

A spreadsheet with photos would be a very good idea.  The key is that, while very few taxpayers are actually audited, if you are audited, the IRS does not have to give you credit for any deduction you can't prove to their satisfaction.

If the donation will be less than $5000, you may still want to get your spreadsheet signed by someone from the charity, instead of getting blank form letter type receipt, so you can show that the list you made actually was donated.

You may want to have an estate sale and donate the cash proceeds instead.

I receive this question on occasion and was wondering about non-cash property held one year or shorter. I read that this is considered ‘ordinary’ income property if sold and is limited to basis or adjusted basis which would be zero. We do also have this as inherited ( if the taxpayer has inherited all their possessions) and may retain the long term nature. Your thoughts are appreciated to settle my wandering mind. 

The cost basis in a gift or inheritance is not zero.  For a gift, your cost basis is the giver's basis (usually what he paid for it). For an inherited item, the cost basis is the fair market value on the date of death.

For an appreciated asset (usually stocks or mutual funds), you may deduct the current value (rather than just your cost basis), but only if the asset is "long term" (held one year or more).  All inherited items are considered long term.  For a gift, the giver's  holding period transfers to you. For example, if Mom gives you a stock she has had for years, it is long term to you, even if you sell it (or donate it) the same day you receive it.