Driver wiring and battery questions

snaps

Newly Enlightened
Joined
Dec 25, 2007
Messages
64
1.
I've just wired 2 of these http://www.dealextreme.com/details.dx/sku.11836 drop ins in series with a 14.8volt battery & the voltage across one is 10.4v & 3.9v across the other. Does anyone have any details of the driver board on these modules or can explain such a big difference?

2.
I use these Li's http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5306347 to drive 4 series connected R2 Crees via a 2.2 ohm current limiting (800mA) resistor in a bike light, but I've had 3 of these packs fail after a few hours use (only output 6 or 7 volts after a full charge cycle) RS have replaced them no problem but I'm getting paranoid it might be something I'm doing!

Any ideas gratefully invited.
 

Mr Happy

Flashlight Enthusiast
Joined
Nov 21, 2007
Messages
5,390
Location
Southern California
Re: Two questions

1.
I've just wired 2 of these drop ins in series...
But...why? Why did you think you could do that? (Hint: you can't wire active LED drivers in series because they will fight each other.)

2.
I use these Li's http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5306347 to drive 4 series connected R2 Crees via a 2.2 ohm current limiting (800mA) resistor in a bike light, but I've had 3 of these packs fail after a few hours use (only output 6 or 7 volts after a full charge cycle) RS have replaced them no problem but I'm getting paranoid it might be something I'm doing!
Let's see. A 4s pack, so when fully charged the voltage will be 4 x 4.2 V = 16.8 V. Four Crees with a voltage drop of about 3.7 V each, 4 x 3.7 = 14.8 V. That gives a surplus voltage of 16.8 - 14.8 volts across the resistor, giving a current of about 1 amp. The discharge capacity of that battery pack is nominal 0.4 A, maximum 2 A, so your current is a little high but within spec. Are you charging it with the matching approved charger?

[Edit: the Vf could be lower than 3.7 V. Say it is 3.2 V, then you would have 4 x 3.2 = 12.8 V dropped, leaving 4 V across the resistor giving 2 amps. Should still be OK as long as you don't destroy the Crees, but worth being careful about.]
 
Last edited:

snaps

Newly Enlightened
Joined
Dec 25, 2007
Messages
64
Re: Two questions

1. I was trying to use 2 of the drop ins on my existing 14.8v batteries, as the vin is 18v each I knew the max would not be exceeded in series & hoped they might draw the same current & give similar illumination.

2. The Vf of the 4 crees is 12.67v & current drawn is 800-820mA (I started with a 6 ohm resistor & reduced the value until I got near my 800mA target) Yes I am using the batterys manufacturers recommended charger. The crees are a Cutter quad MR11 kit mounted in a large alloy light housing that stays cool.
 

Mr Happy

Flashlight Enthusiast
Joined
Nov 21, 2007
Messages
5,390
Location
Southern California
Re: Two questions

1. I was trying to use 2 of the drop ins on my existing 14.8v batteries, as the vin is 18v each I knew the max would not be exceeded in series & hoped they might draw the same current & give similar illumination.
Unfortunately with a variable voltage regulated LED driver it doesn't work that way. Each driver wants to control the current drawn from the supply independently of the other one. When you wire them in series you force the current through each of them to be equal, which removes their freedom to regulate it. As a result they get in a tug of war, in which one of them wins and takes most of the power leaving the other one to drop out of regulation and take what it can get.

2. The Vf of the 4 crees is 12.67v & current drawn is 800-820mA (I started with a 6 ohm resistor & reduced the value until I got near my 800mA target) Yes I am using the batterys manufacturers recommended charger. The crees are a Cutter quad MR11 kit mounted in a large alloy light housing that stays cool.
Then I'm not really sure why the batteries are failing, but you are right to be suspicious of something you are doing. One failure could be chance, two failures a coincidence, but three failures starts to seem like something in the system.

How are you regulating the discharge so that you don't over discharge them? You know you must stop discharging when the voltage drops below 11 V perhaps, and that it will damage the batteries if you discharge below this, or if you rely on the in-built protection circuit to stop them?

The protection circuit is for safety purposes, not to regulate the discharge in normal use. Persistently draining the batteries until the protection circuit activates is very likely to harm the battery pack.
 

snaps

Newly Enlightened
Joined
Dec 25, 2007
Messages
64
Re: Two questions

Yes I looked for circuit diagrams of the drivers but being DX info is a bit scarce!

I've not fully discharged the batteries, as most of my night rides are under two hours so I'm not relying on the protection circuit.
I've orderedsome 18650 batteries from DX to make up my own pack to see if I have better luck.
Anyone make a 4X battery holder for 18650's yet?
 

abvidledUK

Flashlight Enthusiast
Joined
Aug 23, 2005
Messages
2,148
Location
UK
Re: Two questions

Two questions about what ?

Be more specific in header

You can edit it right now
 

yellow

Flashlight Enthusiast
Joined
Oct 31, 2002
Messages
4,626
Location
Baden.at
1. I think You just used the wrong term on "1"
and did wire the inserts in the link in PARALLEL (each one conected to the pack, as if it were alone).
There is no reason and no sense in wiring them in series.

2. at "2" it is easy:
the pack linked does not feature a protection circuit (as is stated in the datasheet! see note ³ at "cutoff voltage")
You simply overdischarged the pack(s).
They are dead

whatever Pack(s) You get now, if there is no protection used (You could see it under the shrink wrap) --> mount a 4-cell protection circuit.



PS: its nice of the shop to replace them but they were not forced to, packs were user damaged
(thats where I get a bit paranoid, because my electronic shop here tended to sell Li-Po packs, also user damaged, as new and it needed some time till I noticed that)
 
Last edited:

snaps

Newly Enlightened
Joined
Dec 25, 2007
Messages
64
Re: Two questions

1. I think You just used the wrong term on "1"
and did wire the inserts in the link in PARALLEL (each one conected to the pack, as if it were alone).
There is no reason and no sense in wiring them in series.

No I meant in series as my batteries are all 14.8v I was hoping they would draw similar current & divide the voltage between them as they don't emit any more lumens above 6.5vin - running them at 14.8v produces the same light but more heat.

2. at "2" it is easy:
the pack linked does not feature a protection circuit (as is stated in the datasheet! see note ³ at "cutoff voltage")
You simply overdischarged the pack(s).
They are dead

The packs DO feature protection, it states that under the Overview in the link to the vendors page which is why I used them.
 

yellow

Flashlight Enthusiast
Joined
Oct 31, 2002
Messages
4,626
Location
Baden.at
forget "overviews"
in the datasheet (what I would use to base technical findings on),
there is just a 7A fuse and the sentence to "cutoff voltage" mentionned

I cant see any info on a "protection circuit" in the sense we understand "protection"
(= over- and undervoltage protection that cuts connection when overcharging/-discharging the pack)
If there were such a device, one would not have been able to overdischarge the three packs

maybe one of the english speaking techies has an idea in interpreting the overview and datasheet?



the led inserts should give the same output, right, but should also draw less current at higher voltage. Heat produced should be the same.
Anyway, way to go is parallel wiring.
 
Last edited:

yellow

Flashlight Enthusiast
Joined
Oct 31, 2002
Messages
4,626
Location
Baden.at
wow, 2 ppl ignoring to read just the one sentence I posted to be read
:rolleyes:

WHAT? does that "protection" circuit do?
The only thing I read is, that there is a 7 A fuse that helps at charging/discharging, if something fails (= means when shorting),
there is nothing (and I mean nothing) indicating voltage protection.

Please be so kind to show which part of overview and especially datasheet refers to such a device
(I still advise to READ what is there under "voltage protection" :rolleyes: and the additional line ³)

Aside from our unnecessary argueing, the result (the three dead packs) unfortunately cearly shows there is no protection
 
Last edited:

MorePower

Enlightened
Joined
Nov 4, 2006
Messages
643
Location
Wisconsin
wow, 2 ppl ignoring to read just the one sentence I posted to be read
:rolleyes:

WHAT? does that "protection" circuit do?
The only thing I read is, that there is a 7 A fuse that helps at charging/discharging, if something fails (= means when shorting),
there is nothing (and I mean nothing) indicating voltage protection.

Please be so kind to show which part of overview and especially datasheet refers to such a device
(I still advise to READ what is there under "voltage protection" :rolleyes: and the additional line ³)

Aside from our unnecessary argueing, the result (the three dead packs) unfortunately cearly shows there is no protection

I'm with you on this one. The datasheet clearly states in the footnote for Cut-off Voltage "This is the voltage at which the pack is considered discharged. If your equipment continues to discharge the battery below the minimum figure indicated, the battery may be damaged and/or its life reduced." Therefore, no low voltage cutoff circuit is built into this battery pack.

Cells were overdischarged and that's why they failed.
 

snaps

Newly Enlightened
Joined
Dec 25, 2007
Messages
64
I've emailed the vendor & maker for more clarification on the protection they speak of.
 

Mr Happy

Flashlight Enthusiast
Joined
Nov 21, 2007
Messages
5,390
Location
Southern California
WHAT? does that "protection" circuit do?
The only thing I read is, that there is a 7 A fuse that helps at charging/discharging, if something fails (= means when shorting),
there is nothing (and I mean nothing) indicating voltage protection.

Please be so kind to show which part of overview and especially datasheet refers to such a device
(I still advise to READ what is there under "voltage protection" :rolleyes: and the additional line ³)

Aside from our unnecessary argueing, the result (the three dead packs) unfortunately cearly shows there is no protection
Sigh... :sigh:

I quote:
Protection Devices:
Electronic Circuit : PLH-2010 x 2 : Polyswitch SRP200

Note 2: Batteries fitted with electronic protection circuits cannot normally deliver current pulses above the maximum figure, since the circuit has short response times.

NB: These devices are designed to protect the pack in the event of control circuit failures e.g. charger failure. They must not be used a main means of charge/discharge control. Protection circuits have response times in the order of a few milliseconds.
Here is a description of the Polyswitch SRP200: http://dkc3.digikey.com/Media/PDF/Data%20Sheets/Tyco%20Electronics%20Raychem%20PDFs/POLYSWITCH_STRAP_(275-300).pdf

It is a fast acting, resettable electronic thermal PTC safety device for building into battery packs.

I accept it is not a voltage-detecting circuit, but it is a protection circuit. It will offer protection against excess discharge currents and against thermal runaway on overcharging. There is no argument that it should not be used for charge or discharge control, only as a backup safety device. I mentioned that in my second post above. I also mentioned in the same post that discharging to too low a voltage could be a problem and that this should be avoided.

So yes, it does not have high/low voltage protection built in. But it does have more than just a 7 A fuse.
 
Last edited:
Top