EN 12845 Diesel Pump Batteries, Chargers and Starters

Two independent batteries, six cranking attempts and constant-voltage charging — what the diesel starting clauses mean on site.

Called out to a logistics warehouse acceptance, we found a single battery in the diesel pump enclosure. The plate was new, the cabling neat, the charger lit — but there was only one. The contractor had meant to add the second later and forgotten. When the test button was pressed, the engine failed to catch on the third attempt, because of voltage drop. Had there been two independent batteries as EN 12845 requires, the system would have switched automatically on the second attempt and the engine would very likely have fired. This article covers the standard behind that scene.

The relevant clauses

The diesel starting system is detailed across several sub-clauses:

• Automatic and manual starting must be independent; the starter motor and batteries may be shared. Nominal voltage ≥ 12 V.
• The automatic starting sequence: six attempts, each 5–10 s, with automatic battery changeover after each attempt.
• Starter pinion engagement, with five additional attempts allowed.
• Two separate battery supplies, to EN 50342-1/2 (lead-acid) or EN 60623 (Ni-Cd).
• An independent, permanently connected, fully automatic constant-voltage charger for each battery.
• Location: on a stand, away from contamination and vibration, close to the starter motor.
• Alarms, both local and at a continuously supervised location.
• Tools and spare parts.

Two independent batteries — why two?

The standard requires two separate battery power supplies serving no other purpose. The reason is not redundancy alone; combined with the automatic changeover logic, it gives the six cranking attempts their practical meaning. If the first battery is weak or has an open cell, the controller switches to the second on the next attempt and the engine gets a fresh chance.

The connection rule we watch for on site: there must be an isolating relay or diode group preventing one battery from affecting the other. We do not accept designs with a single common busbar permanently paralleling both batteries, because a short on one drains the other.

Battery type selection:

• Lead-acid — to EN 50342-1 and EN 50342-2, the most common choice, with electrolyte to the same standards.
• Vented Ni-Cd prismatic — to EN 60623, preferred in tropical climates and where maintenance access is limited.

A hydrometer must be kept in the pump room; we do not sign off maintenance without an electrolyte specific gravity measurement.

Six consecutive cranking attempts — the timing table

The automatic sequence parameters:

Parameter	Value
Total attempts	6
Cranking time per attempt	5–10 s
Rest between attempts	10–15 s
Battery changeover	Automatic after each attempt
Additional pinion attempts (within the engine)	5
After six attempts	Fail-to-start alarm, manual test button active
Nominal voltage	≥ 12 V

The site acceptance procedure: close the fuel line, trigger the automatic sequence, and confirm the fail-to-start alarm operates after six unsuccessful cycles. Then restore the fuel and start the engine from the manual test button. The acceptance record should not be signed without that test.

The automatic constant-voltage charger

Each battery gets its own charger: permanently connected, fully automatic and constant potential. One must be able to be removed for repair while the other continues — so they must be independently supplied, without a shared fuse.

Reference values for lead-acid:

• Float voltage: (2.25 ± 0.05) V per cell — about 13.5 V for a 12 V battery.
• Boost charge upper limit: 2.7 V per cell.
• Output current: 3.5–7.5 % of the 10-hour (C10) capacity. For a 100 Ah C10 battery, 3.5–7.5 A.

For vented Ni-Cd prismatic cells:

• Float voltage: (1.445 ± 0.025) V per cell.
• Boost upper limit: 1.75 V per cell.
• Output current: 25–167 % of the 5-hour capacity.

Charging current must be adjusted for local climate; the same float value may not suit a tropical or very cold cell. "Constant potential" means a modern voltage-regulated charging circuit, not a simple transformer-and-bridge arrangement.

Battery location and room conditions

Four basic requirements:

1. On a stand — batteries do not sit directly on the floor; a profile or composite stand provides vibration and moisture isolation.
2. Away from contamination — oil, fuel leaks, coolant and external moisture must not reach them.
3. Minimum vibration — mounting directly on the pump baseplate is not acceptable.
4. Close to the starter motor — cable runs as short as possible, to minimise voltage drop.

The charger may share an enclosure with the batteries; our standard practice is two batteries and two chargers in a common steel cabinet, in separate compartments. The inside of the cabinet door is labelled with each battery's capacity, date of manufacture and last test date.

Tools and spare parts

The spares that must be kept in the pump enclosure:

• Two sets of fuel filter elements with seals
• Two sets of oil filter elements with seals
• Two sets of V-belts, where fitted
• One complete set of engine gaskets and hoses
• Two injector nozzles

Alongside these, the engine manufacturer's recommended tool kit, a hydrometer and a battery terminal cleaning brush are kept in a locked cabinet in the room.

Typical field errors

• Delivered with a single battery. The case above. A single battery breaches both the two-battery requirement and the changeover logic behind six attempts — grounds for rejection.
• No battery selection function in the controller. If the controller does not change battery on each attempt, it is outside the standard. That requires selection logic in the panel firmware; simple timer-relay systems are not accepted.
• Chargers fed from the fire panel. A panel fault takes both chargers out at once. Chargers should be fed from a supply independent of the main fire AC feed, ideally through a UPS.
• Float voltage set at 14.2 V, automotive style. The standard requires about 13.5 V for a six-cell lead-acid battery; alternator-style settings dry the battery out.
• Batteries on the pump baseplate. Vibration breaches the location requirement, and electrolyte leakage can reach the pump motor windings.
• No hydrometer. If the maintenance record does not log electrolyte specific gravity, the required maintenance regime has not been met.
• Fail-to-start alarm local only. Transmission to a continuously supervised location — a control room or security desk — is required.

Comparison with NFPA

NFPA 20 (2025) defines the diesel starting system similarly: two separate batteries, automatic changeover, and six cranking attempts of 15 s each with 15 s rest, giving a three-minute cycle. EN 12845 uses shorter cranking (5–10 s) with battery changeover after each, so the total cycle is shorter. On chargers, NFPA 20 calls for a two-rate float charger and EN 12845 for constant potential plus boost; in practice the same device satisfies both. NFPA additionally mandates an automatic weekly no-flow test cycle, where EN 12845 describes the weekly test within its maintenance clauses.

Application in Turkey

BYKHY requires two separate batteries and an automatic charger for a diesel fire pump but gives no detail, leaving EN 12845 or NFPA 20 as the reference standard. Insurance surveyors — particularly on FM-compliant projects — test the changeover logic on site: remove one battery, and the engine must still make six attempts on the other. We ask for the panel manufacturer's changeover relay schematic and a record of successful running on the second battery.

Frequently asked questions

Can I certify to EN 12845 with a single battery?

No. Two separate battery power supplies are a "shall" requirement; a single battery cannot pass acceptance testing.

Can the batteries serve other loads, such as pump room lighting?

No. The starting batteries must be used for no other purpose.

What charger output current is required?

3.5–7.5 % of C10 capacity for lead-acid — 3.5 to 7.5 A for a 100 Ah battery. The manufacturer's data sheet should recommend a value in that range.

Is boost charging automatic or manual?

The standard requires the facility to be provided without mandating automation. Modern chargers activate boost automatically when the float level drops; a manual boost button is also accepted.

How often are batteries replaced?

The standard sets no fixed life. Hydrometer checks are carried out regularly, and where specific gravity is low with a healthy charger, the battery is replaced. In practice lead-acid batteries are renewed every four to five years and Ni-Cd every eight to ten.

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