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80V lithium -ion Victa, etc., battery packs

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Chrustie View Drop Down
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    Posted: 03 April 2017 at 8:36am
Hi - I have bought a Victa 80V Chainsaw and made a battery pack for it. It is meant to give me much longer run time (work and live in the bush, off-grid at home), like the back pack sold for Stihl electric chain saws. It starts the saw and runs it for a moment, then the saw switches off, with a bleeping and flashing of lights. There are three contacts in the battery bay of the saw - positive, negative and a third one which obviously is some sort of control circuit which takes a reading of some value in the battery pack and that is used by the chain saws control mechanism. I have no idea what info to feed to this contact, to keep the saw going. Victa customer service refuses to offer any help whatsoever for legal reasons - I wish they'd get their lawyers a real job - and I have been unable to get any information on line so far. I have even used a string of 7x12V batteries to overcome this problem, but same result. Can anyone among you learned folks offer some information to help make this saw run on a 80V to 96V power supply? I can feed in 25amps max with the home-made battery pack at 92V max. and the saw puts out 1200W. Maybe that's not enough and causes a voltage drop? However, the lead acid string shouldn't have that problem, should it? Anyway, hope one of you can help. regards Chrustie.
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Johny View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johny Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 10:43am
It's quite amazing that trawling though various web pages and even finding folk who have re-purposed these 80V batteries, no-one seems to have reverse engineered the "third pin". Most packs and tools appear to have one (a 3rd pin).
My guess is to connect it to battery negative - but that could well blow something up...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote coulomb Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 11:35am
I always thought it was a thermistor, for charging safety, and was able to find evidence supporting this guess with a quick search:



[ From http://electronics.stackexchange.com/questions/10588/why-are-there-3-pins-on-some-batteries, about 40% down the page. ]

Of course, there are many batteries out there, so this may not represent your particular battery. Many posts suggest that some of the smarter batteries actually use the third pin for communications.

But both of those uses are generally for charging, not discharging, the battery. I would not expect a simple tool like a power drill to use that third pin at all, only the charger would, and it's usually a separate item.

Perhaps they are concerned with the battery overheating during discharging as well as charging. They might also be bloody minded, and do a secret handshake with the battery, and if it's not a genuine Victa, forget it.

I just grabbed my Ryobi drill Lithium+ 18 V battery. It measured 6.2V plus to minus. Huh? I put it in the drill, turned it a few times, checked the energy meter (2 of 4 bars), and measured again. 18.6 V. Something strange is going on there.

I measured the resistance from the third terminal to the negative terminal. 8.06 kΩ. I put the pack in the sun for a minute. No change. Operated it a bit, some locked rotor. No change. I put it in the freezer for a minute. No change (to three significant digits, solid). So that indicates either I'm not patient enough, or it's a fake thermistor connected to the third terminal, or it's actually for communications. During this testing, the terminal voltage went back to 6.2 V, and using the drill for 1 second was enough to "reset" it.

You could try measuring the resistance from the third terminal (sometimes marked "T" for thermistor) to the negative terminal, and adding a similar resistor to the chainsaw, in case that's all it's looking for. In my case, I would use a 8.2 kΩ resistor (nearest preferred value). I don't expect the value to be critical (anything from 4.7 kΩ to 12 kΩ might work, for example).

Strange indeed. Manufacturers seem to delight in keeping secrets like this. I hope you or someone here sorts it out soon.

[ Edit: added URL for source page. "confirm this" -> "find evidence supporting this guess". ]

Edited by coulomb - 03 April 2017 at 11:40am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richo Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 12:16pm
Yeah I have modded and repaired a loads of battery packs for tools.
I can confirm it's a thermistor.
If the sun's not up turn your lights ON - duh! Help prevent road rage - get outta my way!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richo Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 12:36pm
Originally posted by Chrustie Chrustie wrote:

It starts the saw and runs it for a moment, then the saw switches off, with a bleeping and flashing of lights.

So either the batteries are at the end of their life or there is a problem with the chainsaw.

Originally posted by Chrustie Chrustie wrote:


There are three contacts in the battery bay of the saw - positive, negative and a third one which obviously is some sort of control circuit which takes a reading of some value in the battery pack and that is used by the chain saws control mechanism. I have no idea what info to feed to this contact, to keep the saw going.


So using a multimeter measure the VOLTS across the three terminals.
Without knowing which one is which ONE combination of terminals will read 0 Volts.
The one that has a reading of 0 volts is the thermister.
So change to RESISTANCE and measure the 0 volt terminals again.
Once you know the resistance you can bypass the temp circuit going into the chainsaw with a resistor and feed in power from a separate source.

If the sun's not up turn your lights ON - duh! Help prevent road rage - get outta my way!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richo Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 12:41pm
Originally posted by coulomb coulomb wrote:

You could try measuring the resistance from the third terminal (sometimes marked "T" for thermistor) to the negative terminal, and adding a similar resistor to the chainsaw, in case that's all it's looking for. In my case, I would use a 8.2 kΩ resistor (nearest preferred value). I don't expect the value to be critical (anything from 4.7 kΩ to 12 kΩ might work, for example).


Yeah what he said
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johny Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 12:50pm
We are all assuming that he has the original pack.
Originally posted by Chrustie Chrustie wrote:

Hi - I have bought a Victa 80V Chainsaw and made a battery pack for it.

Measuring the thermistor only applies to the original pack.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chrustie Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 7:44pm
Thanks for all that great input. I will try a resistor of 8.2 Ohm and see what happens - and I don't have the original power pack to measure. The saw has some sort of load sensing device in it, too, so it is a smart electrical system which might be out of my league as far as modifying the saw to run on my battery pack goes. I may have to buy a 2 a/h battery and settle for a short duty cycle. The damn things are just so expensive and only last for a moment and then need to be recharged.

Thanks again, and if any of you folks have any further insights, I would love to hear. regards   Chrustie    

PS Richo - I have a 91 Handi I drive, and a Subaru Fiori which I wish to electrify if I live long enough to save up for a battery pack - I live 100km from the supermarket and need over 200km range for a return trip.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richo Quote  Post ReplyReply Direct Link To This Post Posted: 05 April 2017 at 12:33pm
Originally posted by Johny Johny wrote:

We are all assuming that he has the original pack.


Ha ha of course - well spotted.

I'd probably just start with a 10k.
Then 22k.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote coulomb Quote  Post ReplyReply Direct Link To This Post Posted: 05 April 2017 at 6:59pm
Firstly, apologies for the late approval of your post.

Originally posted by Chrustie Chrustie wrote:

I will try a resistor of 8.2 Ohm and see what happens - and I don't have the original power pack to measure.


I should have realised you didn't have an original battery / power pack, sorry. The resistor you need is about 8.2 kilo ohms; that little "k" is important, and makes a thousand fold difference. Though go with Richo's suggestion and try 10k ohms first, then if that doesn't work, try 22k. Or get a packet of eight from Jaycar for 55c, and try one, two, or three in series, or even two in parallel or combinations of series and parallel to get 10, 20, 30, 5, 15 etc kilo ohms.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chrustie Quote  Post ReplyReply Direct Link To This Post Posted: 05 April 2017 at 8:31pm
Thanks for that, Coulomb - I will get them in Bairnsdale on Friday or on line if the Jaycar agency there doesn't have them.

greetings Chrustie
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richo Quote  Post ReplyReply Direct Link To This Post Posted: 07 April 2017 at 12:31pm
Originally posted by Chrustie Chrustie wrote:


I have a 91 Handi I drive, and a Subaru Fiori which I wish to electrify


Excellent


Originally posted by Chrustie Chrustie wrote:

I need over 200km range for a return trip.

Ouch.
That'll be about $16k worth of batteries.
You'll need more than one Nissan LEAF worth of batteries.
If the sun's not up turn your lights ON - duh! Help prevent road rage - get outta my way!!
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