Been using bls451 for a couple of years on 5.5V.

Just noticed that the box says 4.8V-6V and the instructions state 4.8V-7.4V

Anyone know if these are safe on 7.4V?

smudge

Anyone know if these are safe on 7.4V?

The only completely correct answer to your question is, "I don't know". But that won't stop me from speculating...

When Futaba specs a servo 7.4 volts they typically mean unregulated LiPos @ 8.4v. I'd be surprised if they were LiPo capable.

I have at least 4 of them still installed. I bought them new in 2007. I don't remember HV being much of a thing back then. Today it is common but back then, not so much. The BLS451 was one of Futaba's first brushless servos and I don't remember any discussion of it being LiPo safe.

Unfortunately I can't find a 451 manual. In my search I found a lot of sites that quote specifications for 4.8 or 6.0 volts but none for 7.4(8.4) volts. Is there any possibility you got the instruction sheet swapped with another servo?

I'm sorry I don't have a diffinitive answer to your question. The best I can offer is to be very careful.

"Well, nothing bad can happen now."

Bls451 specification on box, and leaflet from inside box

Why not just call Ripmax Service Centre and ask the question ?
If you want to have them covered by any warranty, that would be best.

modtron
Oxford UK

That’s an excellent idea! Thank you.

smudge

Bls451 specification on box, and leaflet from inside box

Thanks for sharing and please let us know what you find out.

"Well, nothing bad can happen now."

I do have to say that at the bottom of the sheet on the top of the box, it clearly says 2s lipo.

Logo 700, Specter 700, Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

Yes, but all other specifications and listings state 4.8-6V.

Confused? I am.

I think that maybe it was just the beginning of the changeover to dedicated HV servos. If you ran a 5 cell nicad or nickle metal hydride, that would be a 6v power source, which is why they published the specs for that voltage, but then at the end, they said it could operate on a 2s lipo, but that is just my best gestimate.

Logo 700, Specter 700, Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

smudge

Been using bls451 for a couple of years on 5.5V.

Just noticed that the box says 4.8V-6V and the instructions state 4.8V-7.4V

Anyone know if these are safe on 7.4V?

This topic has been debated several times with no absolute confirmation, let alone from Futaba. Here is link to earlier posting. You can search for other earlier postings on same subject. If you secure confirmation for BLS451 use with 2S LiPo with no voltage regulator, pls post same.

https://rc.runryder.com/t824988p1/

Below is Ripmax response to following question:

Would you please let me know if Futaba BLS451 servo can be used with 2S LiPo battery pack (8.4V max voltage) without voltage regulator?

Response:
Unfortunately we would not advise powering the BLS451 servo directly off of a LiPo pack. The voltage is too high and will likely cause premature failure. You should limit the supply to a five cell NiMH pack or use a 6 volt regulator.

Best regards
Jim Meier

Futaba Service Department
Ripmax Ltd
241 Green Street
Enfield
Middlesex
EN3 7SJ
United Kingdom

Phone: 020 8282 7510

Good job on follow up with credible sources.

Let me ask the OP a few questions:

“why would you want to use 8.4V vs 6V?”
- If you want to have an alternative to nimh pack .. use a LIFE 6V pack

“Are the gains from 8.4v vs 6.0v worth it or do we value “Peace of Mind?”
- Who knows better than the manufacturer?
- Manufacturers recommend operating parameters well below the actual limit of the component to ensure longevity
- However if we push the recommeded value, we are on “borrowed time”

FYI
We fly on 5.6v from Kontronik BEC for years on a 700 class, the model does whatever 3D we want effortlessly.

Not too long ago I asked a similar question about using 8.4 volts on a Futaba FASST receiver that didn't specifically say LiPo safe. It ended much as this tread appears to be headed. That is, Futaba clearly recommends not using 8.4v but anecdotal evidence from modelers that have been doing it for years suggests it can be done.

My personal decision has been to go with the Futaba recommendation even if it is overly conservative. I have no stomach for standing in a field with my model whirring about all the while wondering if some component was running at 105% looking for a time and place to fail. The idea of me walking with my transmitter in my hands and my model in pieces 50 feet away, all the while wondering what happened, is more than I can bear.

With that said I would understand if modelers made a different choice and decided the body of evidence suggest 8.4 volts is acceptable.

https://rc.runryder.com/t825608p1/

"Well, nothing bad can happen now."