Mighty Mule FM500 RB570 Transformer - 18 Volt/40VA - MM UL ONLY
The RB570 transformer is the plug-in low-voltage power source used on many Mighty Mule, GTO and Linear gate operators to keep the operator battery charged. In these systems, the transformer does not run the gate motor directly; it feeds charging power to the control board, and the board maintains the 12V battery used by the opener. A failed transformer can cause low-battery warnings, slow gate movement, intermittent operation, or a dead battery after the system sits for a period of time. However, the same symptoms can also come from a weak battery, damaged wire between the house and control box, corroded terminals, blown fuse, or a board that is no longer charging correctly. For that reason, this part should be matched to the original transformer rating and the correct operator generation instead of chosen by appearance alone.
Compatible With
- Mighty Mule FM350, FM352, FM500, FM502, FM600 and other UL-rated Mighty Mule automatic gate opener systems using an 18 VAC / 40 VA transformer.
- GTO / Linear PRO swing gate operators commonly listed with RB570, including select PRO-SW2000, PRO-SW3000, PRO-SW4000 and PRO-SW4200XL family applications.
- GTO / Linear slide gate operators commonly associated with RB570, including select SL1000, SL2000 and GPX-SL25 family applications.
- May be used with RB709U garage door receiver applications where the original installation manual calls for the RB570 transformer.
- Verify the existing transformer label, control board charging input, and operator manual before using on older or modified systems.
Features & Specifications
| Manufacturer | Linear / GTO / Mighty Mule |
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| Product Type | Replacement AC transformer / battery charger power supply |
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| Part Number | RB570 |
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| Application | Battery charging power for compatible Mighty Mule, GTO and Linear gate opener control boxes |
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| Voltage | 18 VAC output |
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| Power Rating | 40 VA |
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| Compatible Operator Type | Select low-voltage battery-backup swing and slide gate operators |
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| Notes | For UL-rated Mighty Mule and GTO/Linear systems that specify RB570 or an 18 VAC / 40 VA transformer |
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Also Known As / Related Part Numbers
- RB570
- LIN-RB570
- GTO RB570
- Mighty Mule RB570
- 18 Volt / 40VA transformer
- 18 VAC 40 VA transformer
- FM350 transformer
- FM500 transformer
- FM502 transformer
- MM UL transformer
Technician Note
When troubleshooting a charging problem, check AC output at the transformer and at the control box end of the low-voltage wire. A long or damaged wire run can make a good transformer look bad at the operator.
Before Ordering Checklist
- Match the original transformer part number or electrical rating before ordering.
- Confirm the operator is a UL-rated Mighty Mule, GTO or Linear model that uses an 18 VAC transformer.
- Inspect low-voltage wiring for cuts, corrosion, staple damage or long wire-run voltage drop.
- Test or replace a weak 12V battery if the opener still reports low battery.
- Do not substitute a random plug-in transformer with different voltage or VA rating.
Important Ordering Warnings
- Transformer replacement will not fix a failed battery, damaged charge circuit, bad fuse, or corroded low-voltage wire.
- Do not use this transformer on an opener that requires a different AC voltage, DC charger, or solar-only charging setup.
Professional Advisory
Gate operators can start unexpectedly and contain low-voltage and battery wiring that must be handled correctly. Disconnect power before service. If the opener has damaged wiring, missing safety devices, erratic movement, or evidence of surge damage, have the gate inspected by a qualified gate technician.
Product Questions & Answers
What does the RB570 transformer do on a Mighty Mule gate opener?
The RB570 supplies 18 VAC charging power to the operator control box so the battery can stay charged during normal operation.
Is the RB570 the same as the gate opener battery?
No. The transformer charges the battery through the control board. A weak battery, bad wire run, blown fuse, or failed board can still cause charging problems even when the transformer is good.
Can RB570 be used on FM350 and FM500 operators?
Yes. RB570 is commonly used with UL-rated Mighty Mule and GTO/Linear operators, including FM350 and FM500 applications. Always match the original transformer rating and opener generation.
Why does the opener still show low battery after replacing the transformer?
Common causes include a weak 12V battery, damaged low-voltage cable, incorrect wire distance, corroded terminals, bad charging circuit, or a solar/transformer wiring issue.
Is RB570 for older non-UL Mighty Mule operators?
RB570 is generally listed for UL-rated Mighty Mule and GTO/Linear systems. Older pre-UL systems should be checked by original manual, transformer rating, and control board requirements before ordering.
