Guide to combination ground power units that provide both engine start power and continuous maintenance power in a single unit. Comparison of models from Powervamp, Red Box, and ITW GSE.
What Are Combination GPU?
A combination GPU does two jobs in one box: it delivers the high-current burst needed for engine starting and the sustained, regulated output needed for maintenance and avionics work. Instead of buying a battery start unit and a separate continuous power supply, operators get a single piece of equipment that handles both roles. The trade-off is cost and complexity — combination units are more expensive than either component alone and heavier than a pure start unit.
How They Work
Combination GPUs typically use one of two architectures. The first pairs a high-capacity battery pack (for starting) with a mains-powered charger/supply (for continuous output) in a single enclosure. The mains connection keeps the batteries topped off between starts and provides clean continuous power for maintenance. The second architecture uses a large transformer-rectifier that delivers both high peak current for starting and sustained output for maintenance — no batteries involved, but it requires a mains connection for everything, including starts.
Manufacturer Comparison
Choosing the Right Combination GPU
Combination GPUs make the most sense for operators who need both starting capability and maintenance power but don't have room or budget for two separate pieces of equipment. FBOs that service a mix of aircraft types — starting a King Air in the morning, powering a Citation's avionics for an afternoon maintenance check — get the most value from a combination unit.
The sweet spot for most GA and helicopter operations is a combination GPU in the 1,500A to 2,500A peak / 200A to 400A continuous range. This covers the majority of single-engine and light twin turbine aircraft for both starting and maintenance. The Powervamp Coolspool 410 and Coolspool 480 hit this range and have become the de facto standard at mid-sized FBOs worldwide.
Larger operations serving business jets (Challenger, Gulfstream) outgrow combination GPUs and move to dedicated TRUs for starting and separate continuous supplies for maintenance. The current capacity needed for large-cabin jet starts exceeds what most combination units can deliver.
Battery-hybrid combination GPUs need more maintenance than pure TRUs — the battery packs require monitoring, eventual replacement, and temperature management. Factor in battery replacement cost every 3 to 5 years (for lithium) or 1 to 2 years (for lead-acid) when comparing total cost of ownership against separate start and continuous units.
For a step-by-step approach to selecting the right GPU for your aircraft, see our GPU Sizing Guide. For a comparison of lead-acid vs lithium technology, read Lead Acid vs Lithium GPUs.
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Frequently Asked Questions
Is a combination GPU better than separate start and continuous units?
Depends on your operation. A combination GPU is more convenient (one unit, one cable, one position) but more expensive upfront and potentially limited if you need to start one aircraft while powering another for maintenance. Separate units give more flexibility at higher total cost.
Can a combination GPU start any aircraft?
It depends on the peak current rating. A Coolspool 480 at 2,800A peak handles most single-engine and light twin turbines but falls short for super-midsize jets and above. Match the GPU's peak rating to your aircraft's requirements.
How often do combination GPU batteries need replacing?
Lead-acid battery packs in combination GPUs last 1 to 2 years of regular use. Lithium packs last 3 to 5 years. Mains-only (TRU-style) combination GPUs have no batteries to replace. Factor battery replacement cost into your purchase decision.