Surveying with Fenix lights

[Thurly]

During the ICCC expedition to Slovenia, we have noticed that all kinds of Fenix lights (those with magnets on the end such as the HM71R, and those without such as the HM70R) seem to interfere with the disto compass quite significantly. If you are within 1 metre of the disto with a Fenix, be warned as the error may reach up to 100° off a correct measurement.

We actually found that the Fenix-brand 21700 (and 18650) batteries are the main culprit, rather than the torch themselves. Does anyone have any recommendations for 21700 batteries that work in the Fenix headlamps that don’t interfere significantly with surveys? Would be nicer to just have a different battery rather than swap to a whole new torch (we have been using Pixa 3s to survey, as they seem to not affect the compass).

 

[BigDyl]

During the ICCC expedition to Slovenia, we have noticed that all kinds of Fenix lights (those with magnets on the end such as the HM71R, and those without such as the HM70R) seem to interfere with the disto compass quite significantly. If you are within 1 metre of the disto with a Fenix, be warned as the error may reach up to 100° off a correct measurement.

We actually found that the Fenix-brand 21700 (and 18650) batteries are the main culprit, rather than the torch themselves. Does anyone have any recommendations for 21700 batteries that work in the Fenix headlamps that don’t interfere significantly with surveys? Would be nicer to just have a different battery rather than swap to a whole new torch (we have been using Pixa 3s to survey, as they seem to not affect the compass).

I like the actionstash sold 21700s as they’re cheap, I’m not entirely sure if this also has the magnetic issue too tho

 

[Pitlamp]

Thanks for the warning; well worth noting.

 

[SamT]

Hmm - went for a MH60R and thats not magnetic, however, think I've got a Fenix battery in there, so will do a check.

 

[Samouse1]

Hmm - went for a MH60R and thats not magnetic, however, think I've got a Fenix battery in there, so will do a check.

Having done a lot of surveying with this light as well, I've not noticed anything out of the ordinary, and I've only used the Fenix supplied 18650 batteries.

 

[Chris Curry]

Having done a lot of surveying with this light as well, I've not noticed anything out of the ordinary, and I've only used the Fenix supplied 18650 batteries.

This explains all the variations from the original survey data in your Chapel-le-Dale project Todd! And to think you'd been blaming the original surveyors for inaccuracy...

 

[jamesvickery19]

I had a similar problem when surveying G.B. recently, although chalked it up to the magnetic charger on someones headtorch!

 

[martinr]

I was taught to always calibrate the compass at the surface, wearing full caving kit including lamp and batteries, by taking a reading from the entrance to a fixed point some considerable distance away, for which the correct exact bearing was known. Then repeating this when surfacing later.

If either compass reading didn't agree with the known bearing, there was a problem which meant the survey data for the trip would be questionable

It's many years since I did any surveying. Do surveyors today calibrate the compass every trip?