Fixing my dads old jigsaw from nimh to Lipo

[abcdescott]

Back Story

So my dad has worked for a company for about 8 years now and is going to retire soon. just before he started the job hes in he bought a really good bosh 14.4v battery jigsaw and apparently was one of the better ones he has had even tho it was nimh.
When he retired he will need to give back all the tools we have been using so means we either buy a new one or convert this one to Lithium. (not retiring with a lot so better to save where we can expectantly batteries are still like £30-40 for a batter!!)
I made another post here and think this would be a good way for me to start and after this work on my other project that i made a post about.

So I looked into it a bit and bought some stuff yesterday, without realising I should l have came to you guys first.

Plan

I bought some 18650 batteries, holders, BMS board, charger & socket for the charger . Going to install 8 Batteries connected to the BMS which is connected to both the drill connector bit and the charger. I got battery holders because Im not soldering the batteries and wont be making a spot welder - need to see how they fit.

Question

The jigsaw operates at "14.4v" with the 8 batteries and BMS it will be giving out 16.8v I know threes a difference but will it cause any damage, will it be fine or is there a way to lower it to 14.4 ?

Also can someone inform me if the BMS board will cut power when it reaches a low point (safe discharge) rather than draining them too much ?

I can put up some pictures, and the stuff I bought if anyone is interested.

Thanks Guys

 

[Musicmanager]

I bought some 18650 batteries, holders, BMS board, charger & socket for the charger . Going to install 8 Batteries connected to the BMS which is connected to both the drill connector bit and the charger. I got battery holders because Im not soldering the batteries and wont be making a spot welder - need to see how they fit. .. .. .. .. .. .

.. .. .. .. .. .. .. .. .The jigsaw operates at "14.4v" with the 8 batteries and BMS it will be giving out 16.8v I know threes a difference but will it cause any damage, will it be fine or is there a way to lower it to 14.4 ?

The 18650 Lithium battery offers a voltage around 4.2v fully charged which will drop to a steady 3.6/3.7v for most of it use in a charged state, therefore 8 batteries will give you a continuous voltage @ 28.8v or so .. .. . note the voltage 4 would offer.

I had an almost identical project 18 months ago when replacing the battery packs for a collection of cordless drills I use. Although it's possible to make the 18650 fit the units with the correct voltage etc, I ran into some difficulties with the connections between battery packs and unit. You haven't stated which Jigsaw or shown an picture, but I presume the battery pack is the usual, similar to this .. ..

.. .. .. .. .. note the connector tabs at the top of the post; It is a small plastic plate with 3 spring 'tabs' slotted into it, but more especially held in place by one of the Nimh batteries; without that Nimh battery in place, I found it impossible to maintain the position of that plate to give a good connection, resulting in some arcing and the consequent heat.

I concluded that the best action was to replace the Nimh, batteries like for like, which I did successfully and the batteries continue to perform well.

There are folk on here, particularly from the frozen wastes of the North American continent, who will tell you all sorts of tales about Nimh batteries, fakes, and Fred Flintstone but I would take the view that so long as you buy from a reliable source to avoid the fake battery problem, Nimh batteries are an ideal solution to this problem whilst they are still available.

MM

 

[Nigel Goodwin]

There are folk on here, particularly from the frozen wastes of the North American continent, who will tell you all sorts of tales about Nimh batteries, fakes, and Fred Flintstone but I would take the view that so long as you buy from a reliable source to avoid the fake battery problem, Nimh batteries are an ideal solution to this problem whilst they are still available.

Damn expensive though!

A few months ago I rescued a cordless drill from our skip at work - it's a nice Worx one, in a case, two batteries, charger, instructions, and even original receipt - obviously both batteries are shot, but it's very clean overall.

So I've been looking into repairing it - but at work we've got a nice De Walt Li-Ion one, and these only coast about £120 inc VAT brand new with two Li-Ion batteries, and two lot's of NiMh cells to repair the Worx is over half of that.

As part of our core business is replacing battery packs, we have access to decently priced batteries, plus all the other bits, and have a small spot welder to build them up. But I'm still 'dithering' what to do with the Worx - unless it's been chucked out while I've been working from home

 

[Musicmanager]

Damn expensive though!

Yes, agreed, and the comparison between cost of replacement batteries a nice new Li-ion version is a consideration.

However, I have 4 cordless drills in use - largely, because I'm too lazy to keep changing the ends ! - and I managed to get a good deal on 40 Nimh's and I failed to solve the difficulty with the connector block moving around.

MM

 

[rjenkinsgb]

I've done a couple of similar conversions & just got all the parts together to do two more, an old Bosch drill and a battery circular saw.

NiCd cells have a total voltage range of 1.5V full charge down to 1V dead; the typical in-use voltage is around 1.3 to 1.2V, often just taken as 1.2V per cell for overall pack voltage rating.

A 14.4V will have 14.4 / 1.2 = 12 cells and a total working voltage range of 18V down to 12V.

Lithium cells have a voltage rand from 4.2V down to roughly 3.5V
Each lithium cell is near enough equivalent to three NiCd cells; you need four cells in series for a battery pack to give the correct voltage for that drill.

With the eight cells you have, you should have four parallel pairs in series; 2P4S configuration.
That gives an overall voltage range of 16.8V full charge down to 13 - 14V or so near dead.

The voltage range fits perfectly within the original voltage range of the "14.4V" NiCd or NiMH pack.


The BMS board is another matter; there are many variations with similar names, different functions and different ratings.

For one to work in this type of application, it must have both over/under voltage protection, adequate current rating to handle the tool motor stall current without damage - and have "balance" facility.

I'm using minimum 30A (peak)rated boards in power tools, 15 - 20A continuous.

Not all BMS boards have balance & without that, they disconnect the charge as soon as any one cell reaches the maximum voltage, leaving other cells part charged.
With balance, cells reaching near maximum voltage have a load applied across them, eg. taking 50 - 100mA, allowing the other cells in the pack to also be brought up to full charge.

ps. Cheap new laptop batteries on ebay are a good source of ready-tagged 18650 cells; you can get some around 6.6AH for not much more than £10, that contains nine decent quality cells. Just cut the link bars between cells, if they are rigidly connected in the wrong configuration and you have solderable tags to work with; others will already have individual solder tags.

 

[abcdescott]

wow Didn't think this post would get so much interest, Thanks for all the input guys.

So it was actual my dad who put me onto this and he sent me this. and this is what ive been copying.

the BMS boards I got are these, if you think I should get new ones happy to as I want the right one to protect everything.

4S 40A 14.8V 16.8V 18650 Battery Charger BMS Protection Board For Drill Motor C | eBay

Find many great new & used options and get the best deals for 4S 40A 14.8V 16.8V 18650 Battery Charger BMS Protection Board For Drill Motor C at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

and Musicmanager Yeah roughly the same battery as your picture.

Bosch PSB 14.4V battery (1500 mAh 14.4 V)

1500 mAh 14.4 V battery. Partnumbers: 2 607 335 263, 2 607 335 264, 2 607 335 266, 2 607 335 275, 2 607 335 276

www.batteryupgrade.co.uk

In reference to the connector, I was thinking of sealing it in place with superglue under the topside and then when in place clap/hold it whilst drowning it all in silicone to stop movement.

Also the voltage, the bms does show 8 batteries, but its a 14.8/16.8v system ? does this not mean it will only give out that 16.8 fully chargered and 14.8 when dead ?

Cheers guys

 

[Les Jones]

From time to time Lidl sell Li-Ion cordless tools and they also sell the battery packs and chargers separately. I bought some of these and managed to make an adapter (Using part of the old Ni-Cd battery pack.) to use these batteries with a Ryobi drill. This cost less than buying the individual cells and a suitable BMS module. This is a picture of the adapter.

Les.

 

[Nigel Goodwin]

From time to time Lidl sell Li-Ion cordless tools and they also sell the battery packs and chargers separately. I bought some of these and managed to make an adapter (Using part of the old Ni-Cd battery pack.) to use these batteries with a Ryobi drill. This cost less than buying the individual cells and a suitable BMS module. This is a picture of the adapter.

Must say Les, clever idea!

Nice bit of 'thinking outside the box'.

 

[abcdescott]

yeah seen a few of these, but can never find the right adapter, never though of making my own tho .... gd thinking Les !!

 

[rjenkinsgb]

From time to time Lidl sell Li-Ion cordless tools and they also sell the battery packs and chargers separately.

Genius idea!

Aldi do a similar (same?) system, with 20V and 20/40V batteries and chargers. They would be ideal for the nominally 18V saw I've been looking to convert next, just with an appropriate adapter attached to the original battery case top.

 

[Mickster]

Cordless tool battery adapters are on the market:

See the links in the video description for links to Amazon.

Making your own deserves credit, nice job Les.

 

[abcdescott]

So Yeah id love it if I could do this and would but I cant find any power tools using 14.4v these days. why im looking to build my own.

So guys looking for some confirmation here. the nich battery when they say they are charged are about 16.5/16.3v (they arnt even powering the jigsaw to move the motor) So me using the x 8 18650 batteries in parallel means that the voltage would be 16.8v so this is correct yes ?

4.2*8=33.6 /2 = 16.8V Is my maths right or am I just making numbers match my calculations ?

 

[Les Jones]

Hi abcdescott,
Putting Cells (The term battery really means an number of cells in a series / parallel in parallel combination.) in parallel does not give more voltage. It multiplies the ampere hour rating by the number of cells. Connecting cells in series multiplies the voltage by the number of cells. Your last sentence looks like you are planning to have two groups of four cells in series (4.2 x 4) connected in parallel. (Which would give twice the APH rating of a single cell.)
Most battery packs are rated based on the nominal voltage over the discharge cycle of a cell which is 3.6 volts (For Li-Ion) The 20 volt rating is probably a marketing thing to make people think there battery pack is better than an 18 volt pack. A 14.4 volt NiCd pack would contain 12 cells in series (Based on 1.2 volts per cell.) Bu when the cell has just been charged the voltage can be about 1.4 volts per cell so the 12 cell pack would give 16.8 volts at first. So using 4 Li-Ion cells in series should be OK.

Mickster,
Thanks for posting that Youtube. I never even thought of looking if I could buy ready made adapters.

Les.

 

[Nigel Goodwin]

Mickster,
Thanks for posting that Youtube. I never even thought of looking if I could buy ready made adapters.

Les.

Neither had I, who would have thought of such a thing?

 

[rjenkinsgb]

So guys looking for some confirmation here. the nich battery when they say they are charged are about 16.5/16.3v (they arnt even powering the jigsaw to move the motor) So me using the x 8 18650 batteries in parallel means that the voltage would be 16.8v so this is correct yes ?

4.2*8=33.6 /2 = 16.8V Is my maths right or am I just making numbers match my calculations ?

You need to connect them as four cells in series; that's where the 16.8V comes from.

Then another chain of four in series, wired in parallel with the first. The voltage stays the same, but the AH capacity and current ratings are double, as the load is shared between the two sets.

It's abbreviated to 4S2P (or 2P4S) configuration; four cells series, two sets of cells parallel.

Like this, but hopefully with a much higher rated BMS module than in the picture...

 

[abcdescott]

You need to connect them as four cells in series; that's where the 16.8V comes from.

Then another chain of four in series, wired in parallel with the first. The voltage stays the same, but the AH capacity and current ratings are double, as the load is shared between the two sets.

It's abbreviated to 4S2P (or 2P4S) configuration; four cells series, two sets of cells parallel.

Like this, but hopefully with a much higher rated BMS module than in the picture...

Cool thanks for that, Thats what I thought. so I should be good with this configuration.

The BMS I am using is this one https://www.ebay.co.uk/itm/4S-40A-1...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Can you guys advise if this gives the over current protection along with the discharge protection ?

Also can anyone recommend a way to show the battery charge ?