Source: http://forums.aeva.asn.au/viewtopic.php?f=17&t=5593
Timestamp: 2019-04-21 07:09:54+00:00

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I am having a bit of trouble charging my lithium auxiliary battery the way I think it should be charging. The system I have set up is that I have a 12v 90 watt flexible solar panel on the roof of my car. I also have the DC-DC 96v converter which has an on-off switch on the dash board. Both of these go through a PV charge controller which controls the auxiliary battery.
I used to have a Steca charge controller but it seemed to charge the battery for about 10 to 20 minutes then stop charging even if the battery voltage was down around 12.4v and I was still in bright sunlight. I assumed the controller was defective in some way and I probably needed a 12v regulator. I already have two Plasmatronics PL60 regulators which control two different solar systems at my off grid property near Sydney. They charge two different battery banks until the battery voltage reaches around 14.4v. I expected the solar charge controller to do the same thing.
I went to Jaycar and asked for a 12v regulator. When I explained the application to them they said you don’t want a regulator you need a PV Charge controller. I took their word for it and purchased their PV charge controller MP-3722. I installed it but it has exactly the same problem as the Steca charge controller had.
Which brings me to my first question. Can someone explain to me the difference between a regulator and a charge controller?
Secondly. My DC-DC converter is the old 96v converter which came as part of the old “Goombi” kit. After a number of upgrades my car is now working at about 128v dc. I use the converter more often than I would like as the solar panel through the controller keeps cutting out after 20 minutes. The converter however continues to charge the aux battery until I turn the converter off.
I suppose my second question is – do I need to upgrade my converter from 96v to, say, 144v? I have searched and cannot find any 130v converters so I suppose I need a 144v converter?
I am having a bit of trouble charging my lithium auxiliary battery the way I think it should be charging.
Is it 4 LiFePO₄ cells? Or some other lithium chemistry?
I used to have a Steca charge controller but it seemed to charge the battery for about 10 to 20 minutes then stop charging even if the battery voltage was down around 12.4v and I was still in bright sunlight.
How are you measuring the charge current?
It sounds to me like a voltage drop issue. What wire do you have from the charger to the battery (size, preferably as cross sectional area, and length)?
Generally, a regulator is a control device that attempts to achieve a particular set point. In the case of a voltage regulator, the set point is a voltage. So a 12 V regulator attempts to keep its output at 12.0 V. But terminology varies a little; if Plasmatronics call their PL-60 a regulator, then that's true in a sense, but it's more of a current regulator than a voltage regulator. The voltage regulator in an internal combustion car is essentially a voltage regulator, with a set point of some 14.4 V. The alternator has a current limit, say 50 A, so when the battery is low, it may not achieve its set point. But that's fine, it still is pushing power into the battery, and/or supplying some of the "12 V" loads (which are really more like 14 V loads).
I suppose my second question is – do I need to upgrade my converter from 96v to, say, 144v?
That depends on the design of the DC-DC converter. Anything designed for nominal 96 V (8 nominal 12 V lead acid batteries in series) will be able to withstand 25% more than nominal voltage, because lead acid cells under heavy charge can get to 125% of their nominal voltage (15 V per 12 V battery, or 120 V for a nominal 96 V pack). Anything beyond that is generosity.
If you can't find a specification (these things are often hard to find for Chinese made equipment, especially low end equipment as this would presumably be), then you might be able to get some clues from the voltage rating of larger electrolytic capacitors. For example, you might find a capacitor marked 50 μF 125 V. That means it is rated for operation at 125 V continuously, and although it's unlikely to explode at 128 V, its life may be reduced considerably. But perhaps the capacitors are rated at 150 V or 200 V; then the capacitors are not the limitation. Then you should really look at the switching devices. These should be rated at 10% or more, preferably 25%, higher than the pack voltage. So you'd want at least 140 V rated MOSFET(s) for your 128 V pack. Hopefully, you can look up the datasheet for the MOSFET(s) using whatever is printed on the MOSFET package.
Checking the capacitor voltage ratings is a lot easier, so maybe start there to get a feel for what voltages it is expecting.
I have searched and cannot find any 130v converters so I suppose I need a 144v converter?
DC-DC converters sometimes accept a reasonably wide range of input voltages, so searching for a 130 V model might overlook one that operates from say 72 V to 150 V. If you go for a 144 V nominal DC-DC, you should check that it will operate successfully at 120 V or whatever the lowest voltage your pack might reach.
The battery is marked as a Fusion Lithium battery V-LFP-12-26Ah so I assume it is LiFePo.
Both the previous Steca charge controller and the new one show the charge current. When they read zero charge current I know the battery is receiving nothing. I just checked the wire size which is marked as WH-3060 8G Power Cable. My limited knowledge would suggest very little voltage drop with that size cable?
Your explanation seems to match the performance of my existing Plasmatronics regulators. Does a charge controller perform slightly differently?
Thanks for your advice. As I may be adding two more batteries in the near future it sounds like I should get my self a 144v converter as my pack voltage may rise to about 135v dc.
Ok there seems to be missing information here?!?
Can you actually charge your aux battery to 14V by any other method eg lab power supply?
Can you measure the individual cells in the Aux battery?
The reason I ask is it may not be the dc/dc OR solar controllers but the AUX BATTERY.
Have you checked the settings in the MP-3722?
The manual has settings on page 6/12.
Do you actually expect that to charge a 12V battery to 14V?
Most solar controllers will accept a higher voltage (24V PV panel) and drop down to 14V.
Usually they don't boost a 12V panel up to 14V.
Perhaps it's your PV panel.
Under load is it ~17V?
I have a 12v charger which charges the battery up to 13.5v at a rate of 1.7 amps. The battery then sits at 13.4v until I use the car again. The controller will go into what the manual calls "Bulk Charge" for about 20 minutes (if driving during the day) while the panel charges at up to 5 amps. Then the controller shows the pv voltage to be around 2 volts and the current being zero. Bulk charge is supposed to be up 14.3v but the battery never reaches that level.
No I don't think so as I have never tried doing that.
Nope. I was leaving that test until last but maybe the factory defaults are not what the controller is actually doing?
To be honest - yes. The panels on my two solar systems at the country property definitely do. But they are "controlled" by the Plasmatronics regulators. Those panels put out 17v to 21v so should get a battery bank to 14v. Those two systems have been working fine for 16 years.
Don't know. I assumed it must be above 17v to be able to charge the battery for the first 20 minutes or so of each trip?
Thanks Richo for the advice. I will check the controller's setting and the panel's output to see if there could be faults.
... Then the controller shows the pv voltage to be around 2 volts and the current being zero.
That sounds like the problem right there. If the controller merely stopped charging, then the panel voltage should be the 17-21 V you see with no load. Either the controller has gone crazy, or the panel or its wiring is faulty. Since you have tried a new controller with the same result, is sounds like it has to be the panels or wiring. The 2 V could be from energy stored in a capacitor inside the controller. So my guess is that the panel has a crack or other defect that causes the panel to go open circuit after 10-20 minutes in the sun. Perhaps a hair dryer could show up the fault at home, and you might even be able to isolate a particular area, spot the problem by eye, and maybe even repair it.
Solar panel nominal voltages are even more badly chosen than battery voltages. A so-called 12 V panel (nominally 12 V, i.e. in name only) typically has a Vmppt of some 17 V, so you can buck it or even directly connect it to a nominally 12 V battery (which might be at 14.4 V under heavy charge) and still push power into that battery under good solar conditions. So when you use a panel for other than direct battery charging, like the now-common case of a grid interactive solar energy system, its nominal voltage is rather misleading.
Given the battery does charge and both solar controllers are doing a similar thing it does look more towards the panels and its wiring.
1. Did it ever work?
2. When did it stop working?
I think it did a year or two ago. The previous controller didn't give me an instantaneous figure for current charge or pv voltage. I replaced it because I assumed it must have become faulty at some stage. It wasn't until I recently bought a new controller and it did the same things that I thought the problem may not be the controller.
I assumed it couldn't be the panel or wiring as the fault wasn't "permanent". I didn't think a solar panel or it's wiring would always disconnect exactly 20 minutes after exposure to the sun. If the fault had been intermittent I would blame wiring. If the panel never produced any current I would blame solar panel or the wiring.
I will definitely test both over the next few days.
As an off chance it still could be the battery.
Lets say one cell is dead and has a typical output of 1.0V.
So when you charge to 13.5v that means the other 3 cells are charged to 4.1V.
As this battery has an internal BMS it could be doing something when it detects a fault.
So it may take the 20min before it reaches this fault state.
From the other perspective if a fault condition occurs at 3.65V and it only charges, as you say, to 12.4V this would imply a faulty cell at 1.45V.
Most of the chargers have a cutout once the charge current falls below a certain %.
So your pack only takes a charge for 20min as a result of a faulty cell.
The battery claims 10 year life.
So I would hope that this is only a small chance.
I've seen cracked fuses do something similar.
The end cap of the fuse has cracked away from the case.
The 20min of current heats the high resistance spot on the fuse cap and stops working.
But there would have to be a fuse from the solar panel to the solar controller.
I managed to check on the wiring yesterday. My multimeter showed that the controller's display was accurate. I then stripped some of the insulation off the two wires where they come out of the panel which eliminated, as possibilities, voltage drop or some sort of hot spot along the length of the wires between the panel and the controller.
The multimeter reflected the same results as the controller. After about 20 minutes the solar panel's voltage dropped to 1.6v. During that first 20 minutes the panel's voltage always stayed 0.1v or 0.2v above the battery voltage. At that time the battery voltage was about 12.8v and the panel's voltage was about 12.9v.
My gut feel is that it may well be the panel that is the problem. I will take the car to a local solar shop today and see if they can check on the panel for me. I have purchased a number of panels from this shop but I don't know if they are just "salesmen" or whether they have plenty of technical ability. They may, or may not, be able to check the battery for me also.
My investigations were somewhat interrupted by the flu so I didn't want to visit anyone and pass the flu along.
Got to the solar shop today and they basically did the same checks I had already done. We opened the junction box at the base of the panel but couldn't see anything physically wrong with the diode in the junction box. Certainly lots of silicon packing in the junction box. He agreed that if the diode was not working then I would not see any pv voltage at the controller at any stage.
Unless anyone has any further ideas I may just have to buy another panel?
Yep it's a lot of work getting though silicone in the junction boxes.
And it may not be fixable anyway.
But it sounds like the result be will be the same - new panel reqd.
Hi...i am a new user here. In the case of a voltage regulator, the set point is a voltage. So a 12 V regulator attempts to keep its output at 12.0 V. But terminology varies a little; if Plasmatronics call their PL-60 a regulator, then that's true in a sense, but it's more of a current regulator than a voltage regulator. The voltage regulator in an internal combustion car is essentially a voltage regulator, with a set point of some 14.4 V. The alternator has a current limit, say 50 A, so when the battery is low, it may not achieve its set point.

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