Battery upgrade for under cabinet lights.

[Galane]

I got some motion detecting under cabinet LED light bars at a low price. The tiny li-po batteries go with the tiny price. Set the switch to auto and the power they use monitoring the sensor has them working for about a day before needing recharged.

Looks like an easy solder job to swap in some much higher capacity ones. No markings at all on the battery.

The larger chip with 8 pins has no markings. The tiny 6 pin chip at the USB end is a LTH7. Constant current/voltage charger for single cell li-po. Other components are just diodes, capacitors, resistors, and one J3Y transistor in the motion sensor circuit.

The li-po cell appears to not have its own protection for over/under charge.

Would using a larger li-po cell with its own protection work as a direct swap?

 

[Dave_H]

The LTH7 chip is Analog Devices (who acquired Linear Technology) LT40544ES5-4.2, perhaps you found this already. It has a really good datasheet.

No marking on 8-pin SOIC is no surprise, usual case of secrecy i.e. protecting design for copying.

I've entertained this kind of upgrade on a different device. It's possible, just keep in mind the charge rate is fixed. You might be able to live with longer charge time, in exchange for longer operating time.

Up to the limit of the charger maximum current and maximum charge rate of the cell, you could increase charge rate by changing the set resistor. The chip appears good up to 800mA but is spec'ed at 500mA and could be limited to such by a legacy USB port. I think R9 may be the resistor, 3300 ohms which yields 300mA CC charge.

The other resistor 1000 ohms is probably current limiting for the charge LED.

Bumping up to 500mA charge is possible, but increases power dissipation of the chip. It's a tiny device with no thermal pad on the bottom, so it may not like the extra heat.

Is capacity of the current cell i.e. not marked, in the product spec.?

Bottom line, cell swap would likely work as long as it physically fits. Watch heat on the tabs though.

Dave

 

[Galane]

Is capacity of the current cell i.e. not marked, in the product spec.?

Bottom line, cell swap would likely work as long as it physically fits. Watch heat on the tabs though.

Dave

No markings on the cell, product info doesn't specify milliamp-hours or other data. Will a cell with a protection circuit on it work or do I need an unprotected one?

 

[Dave_H]

Not sure, is the original cell unprotected? If so, a new non-protected cell will be no worse.
Unsure if the protection circuit will work with the charger, you might have to try one.

I have seen small cells with protection circuit on a small thin PCB close to where leads enter the cell, but don't see one on yours.

As for capacity, you would need to guesstimate or do some measurements. Let me check some of similar size. Would a tabbed 18650 fit in the case?

Dave

 

[Galane]

They're about 18x25x6 mm. No protection on the cell. I assume the LTH7 and other components are responsible for not overcharging.
Could fit up to 9 or so mm thick. Length can be whatever. Definitely no room for an 18650.

The current battery is about this size https://ydlbattery.com/collections/...um-polymer-ion-battery?variant=42093668794521 Only 150 mAh. Some of the lights I have, have longer batteries, probably 200 to 250 mAh. 250 mAh is the highest capacity this company has in a 20mm wide, flat lipo.

I'm thinking one like this could work. 1,000 mAh https://www.alibaba.com/product-detail/fishing-rod-battery-used-long-rechargeable_60820203834.html

But I just got a quote to ship two of them for $145. $145 to ship two $3 batteries. There has to be somewhere to source 1s lipos in the USA that's not grossly overpriced.

 

[Galane]

These are the lights I got. https://www.temu.com/goods.html?_bg_fs=1&goods_id=601099516568032

200mm and 300mm lengths. The 200mm have the smaller batteries. So do the two 300mm cool white ones I got. The rest are warm white. The warm white ones all came with USB C for charging and a single button function switch to change modes and for multi-step brightness control.

The cool white ones are likely older stock. USB Micro and a three position slide switch for off, on, auto.

The 300mm long warm whites have been going for a few days on motion detecting under the kitchen cabinets. Already had to recharge the four 200mm ones.

The two cool white ones didn't last a day on auto. Could be their motion sensing takes a few micro amps more.

 

[Dave_H]

LTH7 IC will limit current to what it's set to, no problems. These and similar chips are used all over, in small products like this.

150-250mAh sounds way low for something like this, explains the short operating time. 1000mAh would be great if you can fit it, but charge time will be much longer, even if the charging rate can be modified (earlier caveat).

I found a 400mAh cell about the same size, which would be a slight improvement.

The PIR (motion) sensor always draws a small current but should not run a cell down in a day by itself, but it does increase load a bit.

Shipping lithium cells sounds problematic from a safety/regulatory angle, it either legitimately costs a lot, or gives opportunity for the seller to cash in. Perhaps you can find something closer to home, maybe local OTC.


Dave

 

[Lips]

I have 12 or so of the (I think) upgraded model that has cool, white and warm LED's plus dimming with USB C charging. They are flatter than the model you have. Paid $2.22 for most of them up to 7.88 inches...
They have been on under cabinets for 15 days and have not had to recharge any of them yet...



These are on the way now. You can catch the 15.7 inch models on good sales. The larger ones have bigger batteries and you could steal some of those out of them for the smaller units cheaper than you could probably buy a battery... This flatter model may have solved the motion/battery drain issue...

These operational since 8/15/23

 

[Galane]

I have 12 or so of the (I think) upgraded model that has cool, white and warm LED's plus dimming with USB C charging. They are flatter than the model you have. Paid $2.22 for most of them up to 7.88 inches...
They have been on under cabinets for 15 days and have not had to recharge any of them yet...



These are on the way now. You can catch the 15.7 inch models on good sales. The larger ones have bigger batteries and you could steal some of those out of them for the smaller units cheaper than you could probably buy a battery... This flatter model may have solved the motion/battery drain issue...

Have you opened some up to see what size of battery is in them? I found some 1000 mAh Li-Ion cells for cheap on eBay. Dimensions listed should fit in the lights. 1000 out to be a decent upgrade from 200 or 300. The four short lights with USB-C and dimming have the same tiny batteries as the two long ones with Micro B USB and no dimming.

I was able to buy 6 of the 1000 mAh cells so the four short ones and the two long ones will be the first to get upgrades.

Sure, I could just buy some of those other, newer model lights, but I'd still be stuck with all these with too small batteries.

What would be nice is to find a ready made power bank PCB designed to connect multiple Li-Ion cells with proper management. Dunno what I'll do with the ones I take out.

 

[Dave_H]

I found a battery pack containing a cell approx. 40x50x5mm rated 880mAh which is a bit large for this case but is indication of what's possible (if it were narrower and longer).

Might be inconvenient but in the short term, lights could be powered by a USB battery pack feeding the USB input(s).

Dave

 

[Dave_H]

I found a battery pack containing a cell approx. 40x50x5mm rated 880mAh which is a bit large for this case but is indication of what's possible (if it were narrower and longer).

Might be inconvenient but in the short term, lights could be powered by a USB battery pack feeding the USB input(s).

Dave

 

[Lips]

Should arrive today. I'll take a 15 incher apart...

This may be an option. Put 1 or 2 18650 in parallel holder for extended run-times under a cabinet...

 

[Galane]

I got my batteries but somehow the order got changed from 3 pairs to 1 pair, same price. Good news is they're a perfect fit into the lights. Now where can I buy 10 more of these, cheap?

 

[Galane]

Soldered in place of the tiny originals and they work. Don't know how long they took to charge. I have them in motion sense mode on either side of my bathroom mirror. I'll be keeping track of how long they go before quitting.

With the twee little batteries they came with they'd barely last a day, apparently due to the motion sensor circuit using more power than it should. With 5 times the capacity they should last longer between charges.

 

[Lips]

.
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All of mine are going strong a month in, don't need recharging, under cabinets and in-cabinets...
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.
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Yesterday, ordered 9 more 15.7 inch units for the ridiculous price of $1.44 each shipped free.
.

@Dave_H how does this unit look?
Control Chip on Units

11.8 inch and 15.7 inch Light

650 mah with protection circuit on the 15.7 inch unit

Cool White - Warm White - Mixture of both plus Dimming...
(4 Modes) Always on - Night Time Motion - Daytime and Nightime Motion - Off
Sensor Bubble lights up RED when charging and GREEN when done...
Magnets inside and sticky metal pads provided... Easy remove to recharge...

450 mah with protection circuit on the 11.8 inch unit

250 mah with protection circuit on the 3.9 inch unit (Little electrical tape to shade sensor)
Magnets inside the units...

 

[Galane]

They're nicer than the ones I got. Finding a decent price on 102050 lipos is proving to be difficult. Really high minimum order quantities, stupidly high shipping from places that will sell small quantities, or stupidly high price per battery if the shipping is sane.

 

[Lips]

They're nicer than the ones I got. Finding a decent price on 102050 lipos is proving to be difficult. Really high minimum order quantities, stupidly high shipping from places that will sell small quantities, or stupidly high price per battery if the shipping is sane.

Sent you a PM with link to the 15 inch at $1.44 each (free shipping) Can't beat that with a stick!

 

[Lips]

They're nicer than the ones I got. Finding a decent price on 102050 lipos is proving to be difficult. Really high minimum order quantities, stupidly high shipping from places that will sell small quantities, or stupidly high price per battery if the shipping is sane.

I see the 102050 protected Lipo on Alexipress for $1.78 each if you buy 10. (Shipping and tax included)... You can buy any amount for $2.17 + ($1.56 combined shipping) but get a discount at 7 pieces. Here

 

[Galane]

I see the 102050 protected Lipo on Alexipress for $1.78 each if you buy 10. (Shipping and tax included)... You can buy any amount for $2.17 + ($1.56 combined shipping) but get a discount at 7 pieces. Here

Looks like I'll get them there.

There's another thing I forgot, absurdly long lead time. It's September 18th, delivery expected by November 19th. Will it actually take two months? Is October a holiday from Lipo manufacturing in China?

 

[Lips]

There's another thing I forgot, absurdly long lead time. It's September 18th, delivery expected by November 19th. Will it actually take two months? Is October a holiday from Lipo manufacturing in China?

I got 8 x 1500 mah 4mm tall to fit my units for $3 each.

Probably 21 - 26 days from Ali. Could take longer