The charger has a power limit for internal discharging, 80 watts it appears.

Higher discharge rates take either a regenerative or external load setup. Then the full 30A should be available. Regen uses a rechargeable battery as the power source, say a large enough lead acid (auto) battery. The charger basically works in reverse and uses the RC pack to charge the lead acid. External uses an external load, power resistors, light bulbs, etc, to help dissipate the energy.