As long as your grinder likes DC power then your good to go!

Caleb

Yep it won't hurt the machine if grinder is wrong the machine will fry the grinder tho

I agree, I've not heard or seen a machine hurt by it. 

It is the electric tools you must be careful of.  It is best if they note on the info panel that they run on AC/DC.  But many grinders will run on both even if not noted.  I did say 'MANY', not all.  You can generally use this as a determination:  If it has variable speed, don't use it on DC unless it says it is OK on the label/instructions book;  If the switch only powers it on/off, it is usually OK to use DC.  BUT, it is ALWAYS safer and better to use tools that have the rating stated right on them that they are good for AC/DC.

I have not seen any variable speed 9" grinders.  Should be good to go.  I have a 20-25 year old MAKITA that has been used with an old (early 50's,don't have it anymore so I can't check it's exact age with K) SAE 300 on DC many times.  It still runs like a champ.  Sure is heavy compared to the new ones though.

Have a Great Day,  Brent

I had an enthusiastic helper go at it with a 9 inch grinder, bearing down hard, and burned out the exciter on one of my SA200s. Look at the power draw of the grinder - if it's greater than 1 KW (over 8 amps) it's overloading the exciter. You can get away with it for a little while, but watch out if it's heavy continuous use.

Find you an old WildCat. They will work on them.

If it has the older R57 idler and you are going to use the grinder hard for a while pin the idler on high idle.

I used my old wildcat for a lot of years on my redface and never had any problems.

Really old SA-200s had smaller exciters which gave less Aux. power. Most of them give 1750 watts, about 15 amps. There are a few grinders that pull over 15 amps, but darn few.