I was looking for the charge controller section but I could not find it.
I am building a portable little solar system with a Custom built Lithium battery (50ah cells) 12V Daly BMS.
Lithium seems to charge at whatever the max current is you can supply, greedy! So I would need to limit the charge rate.
All the PWM controllers I looked at seem to be aimed at LA & Gel deep cycle.
I am looking for a cheap’ish PWM (R500 - R1000) charge controller that allows me to limit the current output to a specified value. 20A should be sufficient ( I should be able to charge safely at 0.5C )
Something that I can get locally in South Africa, and output should not have any ugly spikes that could damage my BMS
The idea is to charge via mains PSU - maybe an old computer 12V PSU
Charge from a solar panel when out in the bush
Charge from the alternator of a running vehicle if it is cloudy, I do not want to bun out the alternator
To my knowledge, the PWM only controls volts and let the current pass through. The current out will match the current in and the amp rating of the PWM is only to rate the max allowed amps that can be passed through.
If you want a charge controller to limit output current you are going to gave to go with a MPPT.
The idea is to connect the power from the alternator through the solar charge controller to ensure the correct voltage and current to charge my Lithium battery.
A Solar charge controller is a DC to DC… takes solar panel voltage and steps it down to the voltage required for the battery… If it will limit the output current that would also mean that the input current is (limited) unless it burns the excess via heat. I have this at the moment dgm-buck-boost-solar and it works but close to max current I have to run a computer fan to keep it cool and it only allows 10A. Plus the solar panel that I am planning to get has a higher output voltage and would pop the capacitors on this circuit. Thanks for the link I will research the victron unit you suggested
I am not an electrical engineer, my experience is that a mppt is simply a micro-controller looking for the voltage sag from the panel to ensure that we pull the max amps before the voltage goes down ensuring we get the max voltage at the max current. I have seen that the fancy MPPT controllers do allow a max charge current setting but those controllers tend to be way beyond the budget of my build.
ultimately it is still an inductor & mosfet but I am hoping that the current limit works like switched mode power suply with a feedback loop
A PWM charge controller just connects the panels directly to the battery and disconnects them. The average current can be controlled by adjusting the ratio of on time to off time (called the duty cycle), but the current during the on time will be unregulated and will depend on what the PV panels can produce at that time. So it is a good idea to match the PV voltage fairly well to the target battery voltage when using a PWM controller.
A MPPT controller is a bit more complicated because it is a proper DC to DC converter that can drop the PV voltage to the battery voltage while maintaining the PV array at the optimum voltage and current for maximum power. One of the most common methods is to measure the voltage and current to calculate the power and then change the voltage or current target slightly one way or the other to see if the power increases or decreases. If it increases they keep going in the same direction until it decreases and then they change directions again. This is typically called hill-climbing and is a simple way to find the maximum power point, but then you are constantly shifting back and forth just either side of the maximum power point. Another method commonly used is to do a sweep over the whole range from open-circuit voltage to the battery voltage and measure the power at every point in between to find at which point you get maximum power. This is called a sweep and is often combined with hill-climbing so that a sweep is done at certain intervals to make sure that the hill-climbing hasn’t found some smaller peak (which can happen with partial shading).
So if my panel produces 45V you are saying that I will get 45V spikes on the output? I would have thought that those 45V PWM spikes will be driven through an inductor/transformer to step the output down to eg 12V and then be smoothed by a capacitor. Now I was was hoping for a charge controller that will measure the output current and voltage, and apply a feedback loop back to the original duty cycle to ensure I get a stable 20A and 12V (or whatever setting you would input).
To put my requirements simply:
So I am looking for a DC to DC converter that works like a proper switched mode power supply with CV and CC. The only catch is that it must be able to operate from the input voltage range of a solar panel.
If the panel offers 330W of power and my battery is only allowed to charge at 240W then surely the charge controller should not pull full amps from the panel and burn off then excess 90W as heat?
Yes I have a lot of learning to do, sorry for the people that find this frustrating
I have seen this video, it makes perfect sense and I understand why the alternator would get fried. That is why I wish to find a charge controller that can limit output current. Thank you for your input.
Yes, a PWM charge controller doesn’t have inductors etc. that allow it to step the voltage down. You won’t really see 45V spikes on the output though, because the output is connected to the battery, rather you will see current spikes at pretty much the short-circuit current of the panels.
So, yes, you want a DC to DC converter. Basically a buck converter since your PV voltage will most likely always be higher than the battery voltage. When a DC to DC converter or MPPT controller is regulating the battery voltage or current and is therefore not at the maximum power point of the PV array, it doesn’t burn off the excess as heat, it just doesn’t operate the PV array at it’s maximum power voltage and current, so you get less from he PV than is possible, but you don’t mind if the battery is full.
That’s what I was going to say, then I saw you said it already. A PWM controller essentially switches the current on and off in a square wave, where the duty cycle/on-off ratio is controlled by the voltage of the battery. You could of course additionally also control the ratio using current, and then regulate it so that the average current works out where you want it, but…
what Stanley said.
Now the electronics side of this… Capacitors resist a change in voltage (so they are used to give a smooth voltage in DC power supplies), and inductors resist a change in current (so they are used to smooth current flow). So to make the current flow less spikey, you’d have to put an inductor in there. But… once you do that, you essentially have a DC/DC converter, you’re just one component away from having an MPPT.
To add to the other excellent points, the reasons you cannot charge from one battery to another with a cheap PWM…
The source needs to be at a higher voltage or the current won’t flow. There is also a slight voltage drop over the FET in the controller. So unlike a PV module (which is usually a good 5V higher than the battery), you have very little offset (or none at all) to work with in a vehicle.
There is no inherent current control. With a PV module, your switching FET in the PWM controller need only be larger than the Isc (short circuit current) of the panel, and it will never blow up. But when you feed it from another battery, there is no such limit. Your switching FET will blow up.
Ah thank you! the light bulbs are slowly starting to light up for me, this also explains what @JacoDeJongh said earlier, he just said it in less words. I was too ignorant to understand.
Now that I have some “understanding” of the crude way a PWM works I feel like I am much better equipped. I guess I either need to forget about charging from alternator, or buy a MPPT with current limiting capabilities.
If I do decide to go the MPPT route can anyone recommend a MPPT with current limiting capabilities?
Because you will be charging from 12V to 12V, and an MPPT will need 5V above battery voltage to start charging (and 1V thereafter), an MPPT will not work for this. If it was in a truck and you had a 24V battery on the other end, then you had a chance.
Victron makes the Orion DC/DC converter for this purpose. For an MPPT, you’re probably looking at a 100/20. Both these have current limit capabilities, but they are more on the serious end than the cheap end of the spectrum. The other locally made MPPTs (microcare) is not really cheaper, and I would not touch a WRND unless it can be proven that they have improved since I last looked at one.
Ahh, if you want to charge your 12V battery from another 12V battery which has an alternator charging it, that is quite different from charging directly off the alternator output (no other battery on the alternator). You could try one of these: https://www.mantech.co.za/ProductInfo.aspx?Item=372M0015
9 to 18V in, 12V out (adjustable over a small range).
Unfortunately this is the biggest one that Mantech has like that and it only does 50W (Just over 4A output). Unlike the previous one I linked to which has a 24V input (18 to 36V) and does 350W
I already have this LTC3780 DC/DC CC CV Auto Buck Boost Converter 5-32V TO 1-30V-10A and it works pretty well and can at least charge around 100W from a battery + running alternator. I guess this will be the backup strategy for a dual battery system. When mains and solar is not available. I will just mount a 12V fan on top
I guess spending extra money on a cheap MPPT (R1400) will be a worthwhile investment vs just gabbing a PWM (not sure if a PWM charger is all that good for the electronics of the BMS) I paid R900 for my BMS so not small change
Charging from mains (when eskom is available) needs to be more than 12V so the computer PSU is out, something like a 24V 20A Switched mode power supply seems to be the best option , this can plug into the charge controller PV input
