Emergency Lighting - NiMH batteries not holding a charge

[Matt Beattie]

Hi all, new to the forum. 1st post.
I came accross your site by trawling through google searching for possible reasons as to why a number of NiMH 3.6V 1.7ah batteries keep failing the 3 hour discharge test. Some fail after 10mins.
The battery is controlled by a Fagerhult emLED 4/D Non Maintained module for 3W LED. I believe the issue may be caused by overheating. I put a fitting under a thermal imaging camera and found that the driver operates at 33 degrees and the battery sits at 28.
Apologies if this thread doesnt belong on this site.
best regards
Matt

 

[alec_t]

How old are the batteries?
Is the fitting ventilated?

C/10 charge rate for those batteries is 170mA. The spec says Icharge is 210mA. Is that maintained constantly (which would seem excessive) or is there some charge algorithm which terminates charging when some criterion is met?

 

[Matt Beattie]

Hi Alec_t ,
The batteries were first energized in September 2012.
There is no veltialtion for the fitting (please see attached)
The track has a un-interupted supply so the charge is constant with no cut off point. I will follow this reply up with another picture of the battery
Many thanks

 

[Matt Beattie]

Please find photo of the battery

 

[alec_t]

The date on the battery seems to be 06/11? So it may just be suffering from old age.
Although the track has an uninterrupted supply there should be an IC inside the module to manage the charging and terminate it as necessary. A correct charging regime is important for longevity. Check out the NiMH stuff at BatteryUniversity.com

Edit: You may be right about temperature. 28C seems a bit too hot for a battery. Here's what the Fagerhult web-site says:-
"Since some emergency lighting components, for example batteries, are sensitive to temperature the physical solution varies for each luminaire. Some luminaires require the battery or both the battery and the emergency lighting electronics to be moved outside the luminaire and placed in a separate box (battery and emergency lighting box)."

 

[audioguru]

Modern Ni-MH batteries made by Sanyo, Energizer and Duracell hold their charge for 1 year.
Older Ni-MH batteries are dead in about a month or two if they are not used.

 

[Matt Beattie]

Alec_T
can you advise on the IC ? what is that?
Fagerhult supplied the fittings after mackwell installed the batteries. Could it be that the fagerhult driver (ballast) is damaging the mackwell battery ?
both fagerhult and mackwell are taking a back seat to this and are reluctant to send an engineer to site to investigate.
thanks
Matt

 

[Matt Beattie]

Audioguru,
Noted, thanks

 

[alec_t]

can you advise on the IC ? what is that?

There are numerous ICs available. Just google 'battery charge management'.

It's quite possible that the ballast/charger is not matched to the battery, resulting in the battery not reaching full charge or else, more damagingly, being over-charged for long periods. Presumably Fagerhult were satisfied with the batteries already installed or they would have been only too happy to sell you some new ones . Only the two suppliers/installers would be able to say with certainty if there's a mis-match (I wish you luck there ). Have you tried on the phone or online to get an answer?

 

[tvtech]

My original post is worthless. Post editor would not work properly.

Lots to say and maybe help here too. In the meantime, stay well guys

Regards,
tvtech

 

[Matt Beattie]

tvtech , didnt see your original post. Can you offer any advice?

 

[tvtech]

I put a fitting under a thermal imaging camera and found that the driver operates at 33 degrees and the battery sits at 28.

best regards
Matt

Hi Matt

I promised I would reply.

Your problem is the charger has failed somehow. All it appears to be doing is giving you the last kicks from the batteries..without charging...hence the 10 Minute lifespan. 28 degrees Celsius is perfectly acceptable for Nimh, my little PP3's go to around 35 degrees Celsius just after they have finished charging and then drop in temperature and stay there forever. And they are very small and have no issues...

Your temperatures sound a little low though too....sounds like the charger has packed up. No heat = no work done.

So, I reckon, your charger is the culprit. Not the battery age or heat issues or anything else.

Easiest way is to take the batteries out and find a charger on the NET that will charge them properly...to see if they are still good to go.

If they do not charge and all, then your original charger has probably trashed them.

Not the best advise I have ever given...but at least it is a start.

Hope this helps,
tvtech