RCCrawler Forums

XSRCdesign · 08-10-2009, 10:00 PM

Still learning this lipo stuff... Was a little late to this party.

Having a hard time finding a smaller 4s saddle pack.

Any reason why I couldn't purchase 2 2s packs and wire them to act as a 4s saddle?

Charging ok? Etc...

Theser are what I'm thinking of using, and a 25t holmes handwound.

http://www.hobbycity.com/hobbycity/s..._30C_Lipo_Pack

ultimate_monkey · 08-10-2009, 10:04 PM

yup you can wire two 2s onto one 4s, the cells are just like nimh cells in the sense you can wire as many as you want in series, as long as you remember you will be upping the voltage with each cell so you will end up with a 14.8volt pack if you make a 4s, . will your esc handle that? and will the motor take it with out getting to hot? also you will need to add a balance plug for a 4s as well .

and if your charger can caharge and balance 4s packs youll be fine

XSRCdesign · 08-11-2009, 04:59 AM

The esc and charger will both be 4s capable.

Just wanted to make sure I wasn't missing something thinking I could just make my own saddle pack

MadForce · 08-11-2009, 05:31 AM

If you are careful and able in disassembling them then you should do so in order to solder the apropriate balance tab for 4s. If you do not do this then you will have to use some other way to balance the cells. That is important because lipos tend to drain the first cell in series more than the rest quite like all other battery packs.

XSRCdesign · 08-11-2009, 06:15 AM

Is balancing really just for pack life?

I know back in my tc days I balanced matched packs to make them last longer and keep their punch, but never bothered for basher batts...

Reason I ask is I have yet to pick up a balancer yet..

MadForce · 08-11-2009, 06:57 AM

I would not really say that balancing is for pack life only. I said earlier that the first cell is drained heavily in a lipo. So at a 9.9V cutoff you could see cell 1 at 2.8 and cell 2 at 3.6 and cell 3 at 3.5. This has happened many times to packs I use in low drain applications. Now if you charge multiple times a battery discharged like that, you will eventually see the cells unbalance and at full charge they can be like C1:4 , C2:4.3 and C3:4.3. Over time the differences in cell voltage will increase leading to the demise of the pack or even worse to fires and explosions. The chargers in normal mode detect only the ending voltage of the pack thus the pack mentioned above would still give a perfect 12.6v but in reality it is not so perfect.

As far as I am concerned I try to balance the packs as often as possible to help prolong their life and get better performance. Some basher packs I have are being balanced every 3 or 4 cycles but my crawler packs are being balanced in every cycle. I do this because the low drain crawler motors tend to deeply discharge most packs.

XSRCdesign · 08-11-2009, 08:19 AM

Aight, probably should look into a balancer then..

Ill probably just pick up a normal 4s brick pack for now then.

I have plan B for batt placement

sweli · 08-11-2009, 08:28 AM

I have a Torsion rig that had 6cell 2/3A nimh behind the axle in a guard I fabbed. Just recently started running a Lipo saddle pack.
Used two 900mah 2s packs that fit where the nimh cells were.
Each pack has Dean's micros.
Fabbed a 1" long Y-harness (Dean micros into a single Dean Ultra).

Mine are wired in parallel for 1800mah at 2s.
You could do this for yours, but wired in series. Unplug each side of the saddle to charge with it's normally supplied balancing plug, as a 2s pack.

I'll try and post a pic tonight.

Terminator13 · 08-11-2009, 08:30 AM

Any reason you couldn't just make a y adapter and charge them as seprate packs?

ultimate_monkey · 08-11-2009, 08:39 AM

Quote:

Originally Posted by Terminator13

Any reason you couldn't just make a y adapter and charge them as seprate packs?

that would be createing a circut..and just short out the batteries

you would need to run a wire from + on one and the - from the other, as well as you would need a 3rd wire between the packs to keep all 4 batteries in a series just like the 23a saddle packs. You could Y in paralell tho

XSRCdesign · 08-11-2009, 08:46 AM

Thought about the y harness idea..

But charging 2 packs and all the extra wiring out weigh the benefit for me to run it as a saddle in the first place. (For this application)

Terminator13 · 08-11-2009, 08:50 AM

I see, sorry I couldn't be of much help

phillyb · 08-11-2009, 09:22 AM

I see no reason you couldn't wire the two packs together but not sure a balancer would work on that setup, you would have two balancing plugs and only one jack on the charger. I think I have seen balancers that just plug into the balancing port and balance them that way, not sure how that works.

XSRCdesign · 08-11-2009, 10:17 AM

Quote:

Originally Posted by Terminator13

I see, sorry I couldn't be of much help

No worries bud, it was a good idea, just not what I need for this rig.

Quote:

Originally Posted by phillyb

I see no reason you couldn't wire the two packs together but not sure a balancer would work on that setup, you would have two balancing plugs and only one jack on the charger. I think I have seen balancers that just plug into the balancing port and balance them that way, not sure how that works.

I'll look into that, thanks

sweli · 08-11-2009, 10:44 AM

Electrifly has ready made harness' in every configuration you could think of!

http://www.electrifly.com/miscproducts/connectors.html

Two male Ultra to a female ultra in series, weigh 0.42oz
Two male Micro to a female Micro in series, weigh 0.19oz

Maybe it's just me and my COG is so screwed up anyway, but 0.2 or 0.4 oz wouldn't hurt that much.

XSRCdesign · 08-11-2009, 10:49 AM

Weight isn't really the issue....

Having to babysit two packs to charge just to drive one truck? Not my cup of tea

clockworks · 08-11-2009, 10:57 AM

It shouldn't be any problem to run 2 2s packs in series, but you'll need to do some soldering. You just connect the negative lead from one pack to the positive lead from the other, then connect your ESC to the 2 wires that are left.

You can do the same thing with the balance leads - connect the positive wire form one pack to the negative wire from the other, then connect the 5 pins into a 4-cell balance connector. The only thing that you need to watch is that you join the same + and - wires in the balance connector that you joined for the main power cable linking the 2 packs. Get this wrong and you'll let the smoke out.

When you know how a LiPo pack is wired, it'll all make sense. With a 2s pack, you've got 3 wires in the balance connector. The outside 2 are joined, inside the pack, to the same 2 terminals that the power wires are connected to. The middle wire in the connector goes to the "battery bar" that joins the 2 cells together inside the pack.
A 4s pack is the same. The 2 outside wires are the same as the positive and negative, the middle 3 wires go the the 3 "battery bars".

NOTE - I know that at least one manufacturer wires their balance connectors differently, so check with a voltmeter to be safe.

If you want to charge/balance the packs individually, I can't see why this would cause a problem. All 4 cells will still get charged to the same 4.2v.

If I was doing this, I'd get a charger with an onboard balancer and convert both the power and balance wires. It'll make charging and balancing a lot easier and faster.

One problem with charging the 2 packs separately is what happens if you charge one pack, but forget to charge the other. Put them in your crawler and switch on. Your total pack voltage will be around 13v, and the ESC will probably read this as a 3s pack. If you run it until the LVC kicks in, one pack will be ruined.

sweli · 08-11-2009, 02:38 PM

Quote:

Originally Posted by clockworks

One problem with charging the 2 packs separately is what happens if you charge one pack, but forget to charge the other. Put them in your crawler and switch on. Your total pack voltage will be around 13v, and the ESC will probably read this as a 3s pack. If you run it until the LVC kicks in, one pack will be ruined.

Great info Clockworks!

So would it ruin one pack if they were wired in parallel like I'm doing?

clockworks · 08-11-2009, 04:32 PM

Quote:

Originally Posted by sweli

Great info Clockworks!

So would it ruin one pack if they were wired in parallel like I'm doing?

No. If the packs are wired in parallel (2s2p), the fully-charged pack will tend to charge the one that's low. The ESC will still see the pack as a 2s, so no problems.
All that'll happen is you'll get less runtime.

MadForce · 08-12-2009, 03:02 AM

The simpler solution I may think of:
If you want 2 2s packs into one 4s then make a series connector instead of fiddling with the batteries themselves.
As far as charging goes, set your charger for 4s lipo, stay with 2.2A current and use one of these:
http://cgi.ebay.com/Align-XH-JST-typ...d=p3286.c0.m14
Voila, now you are charging both your batts at the same time, balanced and tendered!

08-10-2009, 10:00 PM	#1
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	making a lipo saddle pack? Still learning this lipo stuff... Was a little late to this party. Having a hard time finding a smaller 4s saddle pack. Any reason why I couldn't purchase 2 2s packs and wire them to act as a 4s saddle? Charging ok? Etc... Theser are what I'm thinking of using, and a 25t holmes handwound. http://www.hobbycity.com/hobbycity/s..._30C_Lipo_Pack

08-10-2009, 10:04 PM	#2
ultimate_monkey Rock Crawler Join Date: Mar 2009 Location: Victoria BC Posts: 988	yup you can wire two 2s onto one 4s, the cells are just like nimh cells in the sense you can wire as many as you want in series, as long as you remember you will be upping the voltage with each cell so you will end up with a 14.8volt pack if you make a 4s, . will your esc handle that? and will the motor take it with out getting to hot? also you will need to add a balance plug for a 4s as well . and if your charger can caharge and balance 4s packs youll be fine Last edited by ultimate_monkey; 08-10-2009 at 10:12 PM.

08-11-2009, 04:59 AM	#3
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	The esc and charger will both be 4s capable. Just wanted to make sure I wasn't missing something thinking I could just make my own saddle pack

08-11-2009, 05:31 AM	#4
MadForce RCC Addict Join Date: Nov 2008 Location: Greece, sun, sea and rocks Posts: 1,242	If you are careful and able in disassembling them then you should do so in order to solder the apropriate balance tab for 4s. If you do not do this then you will have to use some other way to balance the cells. That is important because lipos tend to drain the first cell in series more than the rest quite like all other battery packs.

08-11-2009, 06:15 AM	#5
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	Is balancing really just for pack life? I know back in my tc days I balanced matched packs to make them last longer and keep their punch, but never bothered for basher batts... Reason I ask is I have yet to pick up a balancer yet..

08-11-2009, 06:57 AM	#6
MadForce RCC Addict Join Date: Nov 2008 Location: Greece, sun, sea and rocks Posts: 1,242	I would not really say that balancing is for pack life only. I said earlier that the first cell is drained heavily in a lipo. So at a 9.9V cutoff you could see cell 1 at 2.8 and cell 2 at 3.6 and cell 3 at 3.5. This has happened many times to packs I use in low drain applications. Now if you charge multiple times a battery discharged like that, you will eventually see the cells unbalance and at full charge they can be like C1:4 , C2:4.3 and C3:4.3. Over time the differences in cell voltage will increase leading to the demise of the pack or even worse to fires and explosions. The chargers in normal mode detect only the ending voltage of the pack thus the pack mentioned above would still give a perfect 12.6v but in reality it is not so perfect. As far as I am concerned I try to balance the packs as often as possible to help prolong their life and get better performance. Some basher packs I have are being balanced every 3 or 4 cycles but my crawler packs are being balanced in every cycle. I do this because the low drain crawler motors tend to deeply discharge most packs.

08-11-2009, 08:19 AM	#7
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	Aight, probably should look into a balancer then.. Ill probably just pick up a normal 4s brick pack for now then. I have plan B for batt placement

08-11-2009, 08:28 AM	#8
sweli RCC Addict Join Date: Jan 2008 Location: Lake Michigan Posts: 1,898	I have a Torsion rig that had 6cell 2/3A nimh behind the axle in a guard I fabbed. Just recently started running a Lipo saddle pack. Used two 900mah 2s packs that fit where the nimh cells were. Each pack has Dean's micros. Fabbed a 1" long Y-harness (Dean micros into a single Dean Ultra). Mine are wired in parallel for 1800mah at 2s. You could do this for yours, but wired in series. Unplug each side of the saddle to charge with it's normally supplied balancing plug, as a 2s pack. I'll try and post a pic tonight.

08-11-2009, 08:30 AM	#9
Terminator13 Rock Crawler Join Date: Feb 2007 Location: Lorain Posts: 598	Any reason you couldn't just make a y adapter and charge them as seprate packs?

08-11-2009, 08:46 AM	#11
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	Thought about the y harness idea.. But charging 2 packs and all the extra wiring out weigh the benefit for me to run it as a saddle in the first place. (For this application)

08-11-2009, 08:50 AM	#12
Terminator13 Rock Crawler Join Date: Feb 2007 Location: Lorain Posts: 598	I see, sorry I couldn't be of much help

08-11-2009, 09:22 AM	#13
phillyb Rock Crawler Join Date: Nov 2004 Location: roanoke Posts: 550	I see no reason you couldn't wire the two packs together but not sure a balancer would work on that setup, you would have two balancing plugs and only one jack on the charger. I think I have seen balancers that just plug into the balancing port and balance them that way, not sure how that works.

Sponsored Links

08-11-2009, 10:44 AM	#15
sweli RCC Addict Join Date: Jan 2008 Location: Lake Michigan Posts: 1,898	Electrifly has ready made harness' in every configuration you could think of! http://www.electrifly.com/miscproducts/connectors.html Two male Ultra to a female ultra in series, weigh 0.42oz Two male Micro to a female Micro in series, weigh 0.19oz Maybe it's just me and my COG is so screwed up anyway, but 0.2 or 0.4 oz wouldn't hurt that much.

08-11-2009, 10:49 AM	#16
XSRCdesign I wanna be Dave Join Date: Aug 2005 Location: NE Ohio Posts: 8,817	Weight isn't really the issue.... Having to babysit two packs to charge just to drive one truck? Not my cup of tea

08-11-2009, 10:57 AM	#17
clockworks Rock Crawler Join Date: Feb 2008 Location: UK Posts: 818	It shouldn't be any problem to run 2 2s packs in series, but you'll need to do some soldering. You just connect the negative lead from one pack to the positive lead from the other, then connect your ESC to the 2 wires that are left. You can do the same thing with the balance leads - connect the positive wire form one pack to the negative wire from the other, then connect the 5 pins into a 4-cell balance connector. The only thing that you need to watch is that you join the same + and - wires in the balance connector that you joined for the main power cable linking the 2 packs. Get this wrong and you'll let the smoke out. When you know how a LiPo pack is wired, it'll all make sense. With a 2s pack, you've got 3 wires in the balance connector. The outside 2 are joined, inside the pack, to the same 2 terminals that the power wires are connected to. The middle wire in the connector goes to the "battery bar" that joins the 2 cells together inside the pack. A 4s pack is the same. The 2 outside wires are the same as the positive and negative, the middle 3 wires go the the 3 "battery bars". NOTE - I know that at least one manufacturer wires their balance connectors differently, so check with a voltmeter to be safe. If you want to charge/balance the packs individually, I can't see why this would cause a problem. All 4 cells will still get charged to the same 4.2v. If I was doing this, I'd get a charger with an onboard balancer and convert both the power and balance wires. It'll make charging and balancing a lot easier and faster. One problem with charging the 2 packs separately is what happens if you charge one pack, but forget to charge the other. Put them in your crawler and switch on. Your total pack voltage will be around 13v, and the ESC will probably read this as a 3s pack. If you run it until the LVC kicks in, one pack will be ruined.

08-12-2009, 03:02 AM	#20
MadForce RCC Addict Join Date: Nov 2008 Location: Greece, sun, sea and rocks Posts: 1,242	The simpler solution I may think of: If you want 2 2s packs into one 4s then make a series connector instead of fiddling with the batteries themselves. As far as charging goes, set your charger for 4s lipo, stay with 2.2A current and use one of these: http://cgi.ebay.com/Align-XH-JST-typ...d=p3286.c0.m14 Voila, now you are charging both your batts at the same time, balanced and tendered!

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