There are two ways to generate real power on a truck without carrying a second engine: take it off the power take-off, or take it off the engine belt. Both turn the truck’s own engine into the prime mover, and both are far lighter than bolting a separate genset to the deck. Innotec Power builds permanent magnet generators for each, in DC for the vehicle’s own bus and in higher voltages where the load is tools rather than batteries.
The reason to use a permanent magnet machine here is space. Against a conventional PTO alternator the unit is about half the size — a 30 kW machine comes in under 12 inches in length — which is the difference between mounting under the chassis and giving up load deck. Electrical efficiency is over 90%, and there are no brushes, no slip rings and no AVR to fail on a vehicle that vibrates for a living.
PTO-driven generators
The generator mounts beneath the chassis and connects to a drive shaft from the PTO. Shaft speed follows the engine through the PTO ratio — engine speed × PTO% = PTO shaft speed — so the unit is matched to the rated rpm that ratio produces at the engine speed you actually run at. Get that wrong and the machine either never reaches rating or spends its life overspeed; it is the single most important number when specifying one.
24 V — the truck’s own bus
| Model | Output | Rated shaft speed | Voltage |
|---|---|---|---|
| 145-HZ24-060 | 2 kW | 2,600 rpm | 24 VDC |
| 255-FE24-240 | 9 kW | 2,400 rpm | 24 VDC |
| 255-AZZ24-250 | 10 kW | 2,200 rpm | 24 VDC |
Full detail on the 24 V PTO generator page.
48 V — auxiliary and hybrid banks
| Model | Output | Rated shaft speed | Voltage |
|---|---|---|---|
| 145-FZ48-040 | 2 kW | 1,700 rpm | 48 VDC |
| 145-AZZ48-050 | 3 kW | 3,000 rpm | 48 VDC |
| 255-EZ48-085 | 5 kW | 2,600 rpm | 48 VDC |
| 255-DZ48-085 | 5 kW | 3,200 rpm | 48 VDC |
| 255-AEZ48-250 | 18 kW | 2,600 rpm | 48 VDC |
| 255-AZZ48-250 | 18 kW | 4,200 rpm | 48 VDC |
Note the pairs. 255-EZ48-085 and 255-DZ48-085 both make 5 kW, and 255-AEZ48-250 and 255-AZZ48-250 both make 18 kW — the difference is the speed each reaches it at. That is how the range is matched to a PTO ratio rather than asking you to change one. Full detail on the 48 V PTO generator page.
Belt-driven from the engine
Where there is no PTO, or where the truck is already fitted out, the generator can be driven from the engine belt instead. This suits lighter continuous loads and retrofits, and it is the usual answer on a pickup or a van where a chassis PTO was never specified. The belt-driven range runs with a DC automatic voltage regulator across a two-to-one speed range, so output holds while the engine idles up and down. See hybrid belt generators.
Choosing the bus voltage
Match the generator to what the truck already runs, not to the generator you would pick in isolation.
- 24 V if you are charging the truck’s own batteries, running DC tools, or feeding a liftgate, crane or compressor already on the vehicle electrical system. Nothing has to be re-rated. See 24 V DC generators.
- 48 V if there is a separate auxiliary bank, if the run from generator to load is long, or if you are above roughly 10 kW — the same power flows at half the current and the cable comes down a size. See 48 V DC generators.
- 240 V, 400 V or 600 V if the load is mains tools, welding or a site distribution board rather than a battery. The PTO range covers these too — 345-AZZ240-085 and 345-ABZ240-100 at 240 V, 255-BZZ400-025 and 360-HC400-060 at 400 V, 255-BZZ600-025 at 600 V.
Regulated charging, set on site
Output is controlled by DC algorithms rather than a mechanical regulator. You set a minimum and maximum charging voltage against the rpm the PTO delivers, so the generator holds the window the battery manufacturer specifies instead of whatever the engine happens to be doing. On a vehicle whose engine speed is dictated by driving rather than by the electrical load, that is the difference between charging properly and cooking a bank.
Where these go
- Service bodies and utility trucks running tools away from a supply
- Bucket and line trucks where the boom and the battery bank share the engine
- Mobile workshops and breakdown recovery vehicles
- Telecom and utility maintenance fleets charging equipment on site
- Refrigerated bodies and specialist vehicles carrying a DC auxiliary load
- Agricultural machinery and recreational vehicles on the same chassis principle
Or carry a complete set
If the load has to run with the engine off — overnight, or on a site where idling is not allowed — a PTO cannot help, because it needs the engine turning. That is the case for a self-contained unit instead: the 5 kW and 14 kW DC generator sets are built for exactly that duty, and auxiliary power units covers the no-idle argument in full. The whole range across drives and voltages is on the DC generator hub, and heads for customers mounting to their own engine are under engine-mounted generators.
Frequently asked questions
| How much power can a truck PTO generator produce? | Up to 10 kW at 24 V and 18 kW at 48 V from the standard range, with higher outputs wound to order. The limit is usually what the PTO and the engine can give up, not the generator. |
|---|---|
| How do I work out the right model? | Engine speed multiplied by the PTO percentage gives the shaft speed at the generator. Match that to a model rated at or near it. A 2,200 rpm shaft suits 255-AZZ24-250; a 3,200 rpm shaft suits 255-DZ48-085. |
| PTO or belt drive? | PTO for higher continuous output and where the chassis already has one. Belt drive for retrofits, lighter loads and vehicles without a PTO, using a DC automatic voltage regulator to hold output across a two-to-one speed range. |
| Will it fit under the chassis? | Usually. The permanent magnet machine is about half the size of a conventional PTO alternator of the same rating, and even a 30 kW unit is under 12 inches long. |
| Can it run with the engine off? | No. Both PTO and belt drive take power from the running engine. For power at rest you need a self-contained DC generator set or an auxiliary power unit. |
| Does it charge the truck batteries directly? | Yes, at 24 V. Output is regulated DC with a minimum and maximum charging voltage you set against the PTO rpm, so it follows the charging profile the battery needs. |