Am I being too cautious?

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ynot

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Joined
May 28, 2021
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59
Have a 10s (5 leaf modules) and a 10s 2p (10 leaf modules) batteries that I want to run between 38 and 40 volts. Have set my charge controller and/or power supply at 41 volts and they are taking a long time to bring the battery packs up to 40 V, in fact I usually wind up using them before they get to 40 V, would if be advisable to increase the voltage output? The 10s 2p has a BMS so that should cut out if the charger is set high enough. Just recieved a boost converter which I plan on connecting to the 10s 2p bank so I can connect up to the 32 V solar panel that makes a sun/rain/snow shade for the tractor.
Trying to learn here, thanks in advance for any input.
Tony
 

Korishan

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Jan 7, 2017
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6,518
Sounds to me like you need to increase current throughput. Voltage doesn't determine how fast a battery charges, current/amps does.
Now, if the charger controller is switching over to CV (Constant Voltage) before the batteries are reaching 40V, then you may need to change that setting, if you can. You could up to 41V to push that curve out a little further.
But really, if you can up the current, do that.
How much amps is going into the packs now as it is?
 

ynot

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May 28, 2021
Messages
59
Thanks Korishan, I understand that we need amps to charge faster, the power supply is supposed to do 10 amps, and the boost converter is set at 15 amps, but of course it can only deliver 15 amps if the power is there. My fear is over volting and damaging the cells. In our flooded lead acid days we just cranked up the volts, to get more watts, no worries.
Dont really have a decent ammeter so can only trust the settings.
The plan is to have both power supply and boost convertor on the 10s 2p tractor battery, so the solar will be there full time, well in daylight anyroad.
The smaller 5 module pack is experimental, I used it to see how big a string I needed for the tractor and now the same for my freighter trike. Once I build the final trike battery it will have BMS & power supply, not sure I I can put solar on, will have to get it running first.
Tony
 

Korishan

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connect up to the 32 V solar panel that makes a sun/rain/snow shade for the tractor.
Would it be possible to add a second panel? Or perhaps go with two smaller panels to get over 48VDC output. This way you could get the most out of the panels with an MPPT controller. But I do realize that on top of the tractor is prime real estate
If possible, this would also help out as you wouldn't need a "boost" converter, but the MPPT would take care of the bucking down to the proper voltage.

Dont really have a decent ammeter so can only trust the settings.
I don't recall where you are located, but even a $cheap DMM would work. It's relatively easy to figure out how many amps are flowing. Take a chunk of metal like a piece of copper bar that has bolt holes, or even a bolt really. and measure it's resistance from one end to the other. Then connect up the battery to one side, and the tractor/charger to the other side. Set the DMM to voltage setting in millivolts and measure across the bar while the power is flower.
Then use this formula: I = V/R to get the current (I).
Remember that 1000milliVolts = 1V

I just measured a standard zinc coated bolt that's 3/4" long and it measured 0.4-Ohm from tip-tip.
This method may not be 100% accurate, but it may at least get you in the ball park figure.
 

ynot

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May 28, 2021
Messages
59
Great tip about measuring amps............... so much to learn, so little time.
Swapping the PV panel is difficult, "if you have time to mess about with that tractor, you have time to paint the house" she says. <grin>
 

jonyjoe505

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Feb 28, 2018
Messages
229
With a charge controller you might have voltage drop between the controller and battery. Every single controller I ever had, had voltage drop. Anywhere from .5 to 1 volt, this results in less amps going to the battery. No way to fix the voltage drop, the controllers are just not calibrated properly and also the gauge of the wire you use might affect or make the voltage drop worst.
The makeskyblue 60 amp mppt I use has a feature to calibrate the voltage on the controller to the battery terminal voltage. But most controllers don't have a calibration feature, on those you have to raise the bulk voltage way above the recommended to get the required amps going into the battery.
So to your question raising the bulk voltage will definitely increase the amps to the battery. Example on my 4s lifepo4 when I had my ecoworthy 20a mppt bulk set to 14.6 volts (recommended for 4s lifepo4) the battery was charging at 4 amps, when I increased the bulk setting to 15.5 volts (max bulk setting on the ecoworthy) the battery was charging at 12 amps. My lifepo4 was 220ah, 4 amp charge rate wasn't going to cut it.
When dealing with solar and lithium I always use an overvoltage protection relay, that monitors voltage right from the battery terminals, this is extra protection in case the bms fails. On this diagram it shows a 0-40 overvoltage volt relay but you can find 0-99 volt overvoltage relays for about 10 dollars. If the voltage gets too high on the battery terminals, the relay disconnects the solar panel from the controller, this shuts off all charging power to the battery. When you need high performance (charging at high amps) you need the extra protection from these overvoltage relays.

diagram a.jpg
 

daromer

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Oct 8, 2016
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5,659
Only cheap controllers do you need to do that on. A proper controller will meassure correctly from the start.. And high end ones got sense wires even to get it even better. My controller may be 0.2V away but thats at 300A going through the wires and thats the voltage drop in the wires.
The BMS should take care of over voltage if it happens. No need for a 3rd protection. But with that said you can add more. But if you are afraid of the charger doing above you really should ditch that charger asap!

Note that the voltage drop will only be seen at high current and not during final charge. So dont raise voltage....
 

ynot

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Joined
May 28, 2021
Messages
59
Argh.
Buys a boost converter so the PV on the tractor will work....... when the tractor had 4 LA golf cart batteries it worked fine.
Hooked the converter up to a 40V leaf array, with two 12v chargers in series, converter seemed to work, but did not test long enough to see the voltage rise on the battery.
Toddled down to the tractor, checked the output on the PV panel mounted thereon, 36 volts open circuit, oh good, panel still works after a year long holiday.
Installed the boost convertor, no lights come on, check the voltage of the panel input while connected ................ 1.5 volts......... HUHN?
Toddled back up to the shop, got a 12v rv lamp & connected it to the PV panel, no glow, AARRGGHH, dead panel.
Some time this winter maybe will get a chance to put two panels on the tractor in series.
Thanks to all for the input.
Tony.
 
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