An Allen Charge (also known as a "Dynamite Charge") is a term used, usually within the U.S. Federal Court system, to describe the instructions given by a judge to a jury when, after deliberation, it is unable to reach on a verdict. 
The Allen charge dates back to the case of Allen Vs. United States in 1896. The courts ruled that a judge did have the right to strongly encourage deadlocked jurors to continue deliberations until a verdict is reached. Today, there are a number of variations on the original Allen charge text approved in 1896. Some of these modifications have been declared unconstitutional or prejudicial by appellate courts, so individual judges tend to use their own approved Allen charge. A judge cannot force or coerce a jury into reaching a verdict by mentioning the expenses of the trial, for example.
Because of its strong wording, courts have held that an Allen charge can only be delivered once during the deliberation phase.
An example of an Allen charge could read as follows: 
|“|| You have informed the Court of your inability to reach a verdict in this case.
At the outset, the Court wishes you to know that although you have a duty to reach a verdict, if that is not possible, the Court has neither the power nor the desire to compel agreement upon a verdict.
- This instruction as modified was approved by the West Virginia Supreme Court of Appeals in State v. Blessing, 175 W.Va. 132, 133-134, 331 S.E. 2d 863, 865 (1985). This instruction was again approved, citing to State v. Blessing, Supra., by the West Virginia Supreme Court of Appeals in State v. Sloan, 177 W.Va. 585, 588