Lead acid to lithium conversion

Technical discussion on converting internal combustion to electric
Ribfeast
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Re: Lead acid to lithium conversion

Post by Ribfeast » Wed, 13 Feb 2019, 16:37

The main question is how many cells I need to put in, should I aim for 52V, 51V, work off charged voltage or just working voltage etc. ie 4.1v or 3.7v.
On the weekend I might disconnect the charger and measure the voltage it puts out. It’s sitting on 51.5v now with the pack half charged.
It doesn’t appear that I can edit the DeltaQ profile parameters, only switch to a lithium one.

Another option I’m considering is a 0-60V , 0-20A bench/lab power supply and then I can make it do whatever I want. Eg parallel all the batteries for initial balance charge and set it to 4.1V CV etc.
A 20A variant of this:
https://www.ebay.com.au/itm/Digital-KXN ... :rk:3:pf:1

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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 14 Feb 2019, 05:29

I guess 13x NCM cells would be 48V at nominal 3.7V per cell, or 53V at max charge (or charging voltage 53V).
Would this eBay power supply / charger be suitable, or would the cells present such a low resistance that it would overload it? I'm hoping the 20A limit would cut in and it would sit at that current level with the set voltage.

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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 14 Feb 2019, 06:07

Looks like the Delta-Q 48V charger can put out up to 72V, question is how much voltage the lithium profile is set to (hoping around 53V). Not sure if the charger will let me run it without a battery attached to find out, and I'm not getting any response from their support which is frustrating...

https://www.springers.com.au/product/de ... y_charger/

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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 14 Feb 2019, 07:07

http://www.farscape-1.com/lithium-ion-g ... batteries/
https://www.elitepowersolutions.com/gol ... ry-system/

Appears there are some conversion kits out there, Delta-Q even makes a custom charger for the EZ-GO lithium golf carts.
From what I can tell, it's a 16S1P arrangement, which implies 16 LiFePO4 cells. This would be 51.2V nominal, 58.4V at 100% SoC. I've lodged another e-mail to Delta-Q to find the output voltage on those profiles.

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Re: Lead acid to lithium conversion

Post by coulomb » Thu, 14 Feb 2019, 08:07

Ribfeast wrote:
Thu, 14 Feb 2019, 05:29
Would this eBay power supply / charger be suitable, or would the cells present such a low resistance that it would overload it? I'm hoping the 20A limit would cut in and it would sit at that current level with the set voltage.
It would current limit; all battery chargers do that. It would not get to the set voltage until it's nearly full. During the so-called bulk stage, the charger delivers maximum rated current, and the battery voltage slowly rises (perhaps over many hours) till it reaches the set voltage. It should stay at that voltage during the absorb phase, and the current should drop off until a certain low value, when the charge is over. Those two values, the set (absorb) voltage and the cutoff current, are the two main parameters for any charger. Some chargers have a fancy algorithm with various stages of constant current or constant voltage, but that's all that's needed.

Often the cutoff current isn't mentioned. Usually you just need a charger that can take the battery from empty to full in roughly 6 hours; then the cutoff current will be roughly right for most batteries. A charger that is way too small or way too large will have the wrong cutoff current. If that's really a 25 A 1200 W charger (the specifications seem to say 13.5 A and 650 W), then that sounds about right; perhaps a little on the small side.

It's certainly frustrating when manufacturers don't provide enough information to make an informed purchase decision.
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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 14 Feb 2019, 11:06

Yeah I have had a few replies from Delta-Q, they are tight lipped about the specs and say they are proprietary. I've done my own research and from what I can tell, the Samsung SDI 20 profile is designed for a 16 cell LiFePO4 pack, so this is the likely path I will take.
The 650W charger is indeed quite small but it should have the unit charged up in around 7-8 hours I'd hope. May upgrade the charger later to a 1200W (or larger) if I can justify it.

Just wondering if that cheapie eBay variable lab/bench power supply would be suitable enough for the initial parallel charge process and maybe as a backup for the main charger later.

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Re: Lead acid to lithium conversion

Post by Richo » Thu, 14 Feb 2019, 12:59

Ribfeast wrote:
Thu, 14 Feb 2019, 06:07
Looks like the Delta-Q 48V charger can put out up to 72V, question is how much voltage the lithium profile is set to (hoping around 53V).
Not sure if the charger will let me run it without a battery attached to find out,
and I'm not getting any response from their support which is frustrating...
In the good ol' days you would just select your battery chemistry type.
The charger then checks your battery voltage and work out how many cells you have then start charging.

This thing about having 200+ "profiles" in the charger is a bit backwards.
All that happens is they end up with a lot of calls for customer support.
Then they get sick of it and don't respond to a lot of them.
And then customers get frustrated.
It all went down hill when the engineer came up with a stupid idea to solve a problem.

All things considered IF they are using 3.7V cells they would need 13 cells to make 48.1V as their "48V" lithium profile.
So your thinking about 53.3V terminating charge voltage would be correct.

So you need your pack to be equal or above this.
So LiFePO4 would be 15 cells. 48V nom. 54.7V charge.
So charging to 53V would loose almost nothing as a useable capacity.

For NCM it would be 13 cells. 46.8V nom. 53.3V charge.

Still it's a lot of IF's.
Hopefully Detla-Q will get back to you.
So the short answer is NO but the long answer is YES.
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Re: Lead acid to lithium conversion

Post by Richo » Thu, 14 Feb 2019, 13:01

Ribfeast wrote:
Thu, 14 Feb 2019, 11:06
the Samsung SDI 20 profile is designed for a 16 cell LiFePO4 pack, so this is the likely path I will take.
Richo wrote:
Thu, 14 Feb 2019, 12:59
So LiFePO4 would be 15 cells. 48V nom. 54.7V charge.
So charging to 53V would loose almost nothing as a useable capacity.
Hmmm 15..16..
So the short answer is NO but the long answer is YES.
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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 14 Feb 2019, 13:02

OK order has been placed for 16 LiFePO4 cells, Zeva BMS, safety contactor, monitor screen for BMS, temp sensor, cell interlinks. Just need to obtain a bench power supply to provide the initial 3.65V balance charge.
Other things to get will be a flyback diode for the contactor to protect from HV spikes, and maybe something similar to protect the BMS.
Am going to take a punt that the Delta-Q is suitable, otherwise will hunt down a suitable charger as required.

Once all the bits arrive I'll get some threaded rod, nuts and washers so I can lightly compress the pack, and then mount the whole thing in a foam-lined box for vibration protection.

Thanks everyone for their input, greatly appreciated :)

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Re: Lead acid to lithium conversion

Post by Ribfeast » Fri, 15 Feb 2019, 07:08

If the pack were to disconnect due to a low voltage shutdown, would a TVS diode like the one below be suitable to absorb the HV spike generated by the motor when its power is cut? Just trying to protect the Sevcon in case someone ever ran the battery too low and it shut off, or if regen braking exceeds limits and the Zeva cuts the pack also.

Breakdown Voltage Min:
64V
Breakdown Voltage Max:
70V
Reverse Stand-Off Voltage Vrwm:
58V
Clamping Voltage Vc Max:
110V
Good for about 6kA pulse apparently?

https://www.ebay.com.au/itm/1pcs-PTVS6- ... ctupt=true

https://en.wikipedia.org/wiki/Load_dump

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Re: Lead acid to lithium conversion

Post by Richo » Fri, 15 Feb 2019, 12:55

The flyback diode goes on the 12V side of the contactor.

The controller should have motor protection on the HV side.
Even less requirements to add something for 3-phase design.
Normally it's not a TVS diode anyway.
Just a rectifier diode pointing from -HV to +HV.
Something like an APT60S20BG would probably be ok.

You could add a TVS if it makes you feel better.
e14 has them cheaper 2420365.
So the short answer is NO but the long answer is YES.
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Re: Lead acid to lithium conversion

Post by Ribfeast » Fri, 15 Feb 2019, 13:03

Ah if the controller has HV protection then it should be OK. Have to check if the Zeva BMS has similar protection. Thanks Richo :)

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Re: Lead acid to lithium conversion

Post by T1 Terry » Fri, 15 Feb 2019, 19:46

Ummm... a bit late to be joining the conversion but I've been on the road and out of range for a far bit.
A second hand Prius battery from the wreckers for around the $400 mark, reconfigured to 7 modules would be 45.5v min and 56v max. Each module is 6.5Ah and there are 28 module in the pack. 4 x 7 modules from a pack, 6.5 x 4 = 26Ah. Recharge after each outing would require 56 x 26 = 1456Wh or 2 1/4 hrs per recharge with your 650w charger. each module can handle 120 amp discharge because that is what the suffer all the time while operating in a Prius, plus up to a 100 amp recharge on regen. $ modules in parallel could put out 480 amps under load and 400 amp regen recharge ....
Actually, where can I buy one of these things so I can refurbish it with a battery pack that will do a better job than anything offered at the moment at a fraction of the cost ;) 8-) :lol:
As far as a BMS, cell voltage monitoring and cut the mains supply when any cell reaches the desired max voltage, it doesn't get much easier than that. Forget about all the tricky and trendy stuff, you want functional not the latest in fashion :D

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Re: Lead acid to lithium conversion

Post by Ribfeast » Wed, 20 Feb 2019, 05:45

Batteries have arrived, I've made up a temp bus bar out of some aluminium flat bar for the initial balance charge. 3.2V 1600Ah, wouldn't want to drop a screwdriver on it!

https://imgur.com/a/6o6j5A8

Just waiting on BMS and charger. Charger might be a few weeks :(

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Re: Lead acid to lithium conversion

Post by Ribfeast » Mon, 25 Feb 2019, 05:57

Battery box built :)

https://imgur.com/a/IlTpuF9

Have configured as 4S4P temporarily and attached to a gel charger for a few days while I wait for the variable power supply to arrive. It's just hit the country so hopefully I'll see it soon. Will then reconfigure to 16P and finalize the balance charge.

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Re: Lead acid to lithium conversion

Post by Ribfeast » Thu, 28 Feb 2019, 06:48

Power supply has arrived and I have been performing a balance charge for the last few days. Have the power supply set at 3.45V and it has been hovering at around 8-10A output without dropping (bank is wired as parallel, ie 1600Ah). Pack is sitting around 3.35V.
Around 1.7kwh has been sent to the pack plus whatever I put in with the 12V car charger before I started metering it, may stop the charge soon and do a final 3.65V charge just before I finalize assembly (don't want to leave it fully charged for too long).
Pack is 5kWh and I'm not sure what percent charged the cells arrived at, but they arrived with 3.275V each, am worried about overcharging it, even at such a low input voltage.

https://imgur.com/a/uNbcTN5

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Re: Lead acid to lithium conversion

Post by Richo » Thu, 28 Feb 2019, 12:23

3.45V will get the pack 80-90% full but won't ever over charge them.
Eventually the current will drop back to the total leakage current (mA).
4 days to go...
So the short answer is NO but the long answer is YES.
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Re: Lead acid to lithium conversion

Post by T1 Terry » Fri, 01 Mar 2019, 10:47

If the cells won't hold better than 3.5v over night with nothing attached to discharge them, then they are not fully charged. Very important to fully charge the cells before the first use and equally important not to push any cell much over the 3.6v mark and hold it there for long periods if you want to pull high currents out of the cells and not suffer serious voltage drop.

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Re: Lead acid to lithium conversion

Post by Ribfeast » Sat, 02 Mar 2019, 09:33

Wired it all up yesterday with BMS etc and took it for a spin, runs like an absolute animal now, goes up hills like they aren't there, seems to peak at around 185A draw with just me in it on a moderate 30 degree hill. Drove it to a mate's place and we took it up a 45 degree hill together and hit 300A and it went up without breaking a sweat.
Continued on to the horse feed shop (5km round trip) and loaded around 100kg of feed bags in the back and drove it back home, still sitting on 79% charge.
I'm giving it another full charge to confirm it is actually full, BMS seems to be doing a good job of keeping cell balance in check.
Will put up some photos and videos soon once I have prettied things up a bit.

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Re: Lead acid to lithium conversion

Post by Ribfeast » Mon, 04 Mar 2019, 06:35

Some pictures :)

https://imgur.com/a/pH8l9tN

Just need to do a few tweaks to the voltage limits for charging etc, currently it is set a bit conservative. I'd also like to upgrade the white battery monitoring wires to thicker ones so that the current shunting works better, I think they are a bit thin.
All in all a successful project, thanks everyone for their advice!

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Re: Lead acid to lithium conversion

Post by T1 Terry » Mon, 04 Mar 2019, 12:05

Do you think one of these beasts could push a 3 tonne caravan into a workshop on flat level ground? Buying one with an exhausted battery and repowering it would make a great workshop tractor if it could push/pull that sort of weight.

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Re: Lead acid to lithium conversion

Post by Ribfeast » Tue, 05 Mar 2019, 05:17

It probably could, I know the brakes on mine wouldn't be up to stopping it on any kind of slope though.
It would need to have a towball fitted etc, and would definitely be well outside the rated towing capacity.
But if it is just on level ground I reckon it would be fine.

I've put a tow hitch on our 23hp diesel lawn tractor (Kubota BX2370) and it tows a box trailer around the farm just fine, but struggles to drag it up slopes when it is full of soil.

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Re: Lead acid to lithium conversion

Post by T1 Terry » Tue, 05 Mar 2019, 14:09

Í just need something to push caravans into the workshop to do the solar and battery install and then drag it back out. We used a one wheel caravan mover for a while but its steering gearbox tore the teeth off the gears with a rather front heavy van and now requires kick steering. The other issue is traction, it tends to dig holes in the gravel.
When I read about the units like yours going relatively cheap with a dead battery I thought about getting one and using that. It could double as a handy yard/garden unit for both the workshop and the house.
You mentioned there were a number of these units advertised but very few takers, can you share a link as to where these are advertised?

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Re: Lead acid to lithium conversion

Post by Ribfeast » Wed, 06 Mar 2019, 05:31

Farm Machinery Sales (.com.au) had a few when I looked recently, cheapest was still around $8k or so though.
TradeFarmMachinery has some too: https://www.tradefarmmachinery.com.au/d ... man-653170

These are also something I considered at the time:
http://pickman.com.au/listings/pickman-kw4wh1/

Bloody cheap for a brand new UTV.

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Re: Lead acid to lithium conversion

Post by brendon_m » Wed, 06 Mar 2019, 07:10

A little electric forklift could probably be picked up for less than that. Even a walky type might suit.

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