Variable Power Supply and MPPT for charging LifePO4 bank

[Baserati]

Im building a 200 Ah 48v supply for my boat. I want to use the following to charge it. Does anyone see any issues?

Power Supply =Xantrex XFR 60-20 DC Power Supply (60v 20A adjustable)
MPPT = Victron Energy SmartSolar MPPT 100V 20 amp 12/24/48-Volt Solar Charge Controller (Bluetooth)

Main Reason I want to do this is twofold

1) I may add solar to back of boat to maintain charge
2) I want to be able to keep batteries at about a 70% SOC and then only charge them to 100% just before sailing. Need a charger that can get me there in about 3 hours

 

[Tecnodave]

I see a huge problem with that that will cause problems...first let’s talk about “soft” sources of power vs “stiff” sources of power.....we start with the solar panel..it starts at VOC with no current and then when you load the panel down with current draw the voltage will drop until it goes to zero with a big enough load....this is a “soft” source

On the “stiff” sources there are batteries, power supplies etc that will not drop in voltage until you have overloaded it

The MPPT controller works by unloading the panel, gets a voltage and current, logs it then ramps up the current , measures current and voltage, then repeats this pattern until it builds up a data base of where the solar panel is putting out the most power then it loads the panels to that voltage and current...That is finding the MPP......the Maximum Power Point.....this is where it will operate the solar panels.....that is why it is called a MPPT......”Maximum Power Point Tracking“ charge controller there may be several dozens or more tracking points logged in determining where to operate the panels. The controller will keep sweeping the voltage/current to keep the panels at MPP regardless of pop up clouds, etc. This can be observed with an oscilloscope, it happens way too quick to see it on a typical DMM

Now then when we feed a MPPT controller with a stiff source it cannot load down the power and find the maximum power point

Wrong tool for the job....What you need here is a PWM controller these are fancy series regulators which can easily do this job, they are less efficient than MPPT controllers but it’s not a problem in this case....with stiff power

Get one rated for more current by at least 30% because you do not want to run electronics at 100% of capacity continuously

My favorite.......The Antique Trace C-40 , been around forever, cheap, works forever, rugged . lots of heat sink

david

<edited multiple times to correct appleautobutchermyspelling>

 

[SolarForU2]

I take it you will use the adjustable PSU to charge batteries to a lower set point like 3.335 v\cell or 53.36v for your lower state of charge.
Then use the mppt charger with PSU set to higher voltage OR use PV panels on the boat to top them up prior to or during sailing.

Contrary to Tecnodave, your scheme will work fine, MPPT chargers work equally well from other power sources, if your PSU has a constant current set to 20 amps (not a current foldback) then the charger will easily locate the max at 20 amps. 60v may be a little low for it however as it will only be 4v below the max battery voltage (3.5v\cell x 16) ; Try it and see, I would use a higher voltage like 70-80v.
If 60v is too low then as Tecnodave says you would have to go with a PWM charger and put up with it being less efficient running off PV.

Mike

 

[Tecnodave]

Mike,

if you are going quote first read the post, you obviously do not understand the issue
do your research, tell me that a MPPT Controller is designed to do that....

been doing solar since mid 60’s
electrical engineer
beta tester for a major AMERICAN manufacturer of the very best MPPT controller there is. . can you name that controller? dought it.....

 

[snoobler]

Mike,

if you are going quote first read the post, you obviously do not understand the issue
do your research, tell me that a MPPT Controller is designed to do that....

been doing solar since mid 60’s
electrical engineer
beta tester for a major AMERICAN manufacturer of the very best MPPT controller there is. . can you name that controller? dought it.....

Dozens of examples of this working exactly as the OP desires. Will does it too.

Here's the owner of MidniteSolar saying it will work:

Testing MPP Charge controller function with bench power supply?

Anyone know if you can use a 5A-60V DC power supply to test functioning of a MPP charge controller. I have a all in one inverter with charge controller that I am testing in my shop before shipping to where it will be installed in MX. Everything is working great but don't have PV panels here and...

diysolarforum.com

 

[SolarForU2]

Mike,

if you are going quote first read the post, you obviously do not understand the issue
do your research, tell me that a MPPT Controller is designed to do that....
.. can you name that controller? dought it.....

As an electronics engineer 40+ yrs, whom designs and builds PV controllers and high power industrial inverters, MPPT controllers work fine off a regulated PSU with a constant current setting, please read my original post again.
I test all my designs of MPPT controllers on the bench using a CV, CC variable PSU, no problem. I presume the OP Xantrex PSU is such a device, from his description.

You are correct in that it would not be wise to test it on a PSU that didn't have a CC set, unless the MPPT controller had inbuilt max current limiting such that the PSU didn't get over loaded. In one commercial installation we have done the backup PSU with generator input supplies a MPPT PV charger that limits charge current to a set value (60 amps currently), PSU can supply 80 odd amps and doesn't have any CC limiting, never had any issues.

Cheers
Mike

 

[Tecnodave]

I’m not saying you cannot do that, I’m saying there is a better way to do it.
i got scolded for my reply to you , if you are offended, I will apologise. I too am an electrical engineer...but my expertise is radio communications, as such solar was used extensively in our work as VHF/UHF radio equipment is often located remotely on mountain tops where electricity is not reliable. I don’t mean to offend , I came to this site to share and research lithium batteries, I’ve got some very strange ones

 

[SolarForU2]

Hey no problem, I worked > 20 yrs with high power AM, FM, UHF, TV and uWave radio transmitters, great industry, don't miss 3am call-outs at all, now retired.
Hope Baserati gets his setup working ok.

 

[Tecnodave]

I worked in the 30 MHz to 950Mhz land mobile, aircraft bands mostly for a huge electric company >20 years,
long since retired and I don’t miss the night calls either went into computers at slavegate, bailed outta there, don’t miss that part, root cause failure analysis, slave you to death

 

[Baserati]

Thanks Guys. I will digest and let you know if I have more questions

 

[Baserati]

Ok so I have a further question
I have been testing a Xantrex Power Supply. You can set voltage and current as well as activate the over voltage protection on the power Supply. Why would I not just use this as my charger. Do I need an MPPT or PWM at all?

 

[HRTKD]

If the power supply is truly programmable and it will accept the charge profile you want to use, then I see no reason to not use the power supply.

 

[ed209]

@Baserati How did it end up working?

I have a similar situation where I want to feed a 12v cigarette port through a constant current voltage booster to an MPPT controller.

I'm building a battery that has alternator and solar charging. In my vehicle I have alternator charging set up. When I bring my battery to another vehicle, I want to be able to easily tap into the 12v for some slow (100 watt) charging while driving.

 

[Baserati]

I have not made much progress, hopefully over the next few weeks.