Discussion in 'Hobby Engineering' started by Mathuisella, Oct 15, 2013.
Mc4 connectors and fun
My balancer and bms rocked up. I have not had a chance to play with them as I still need bus bars to link up my first 4 cells. Racking tomorrow! All getting very exciting!
Julian Illet does great solar based videos, he's even designed his own solar pwm charge controllers, messes with boost/buck converters, and other power related toys. I saw this video the other day - Theres also another guy "DavidPoz" and "DIY Solar Power With Will Prowse", Both aimed at beginners, but I learned a lot about Lithium batteries from these two guys. David plays with Lithium Ions (same as 18650s, but bigass packs salvaged from electric cars), and Will plays with the LifePO4 prismatic cells, similar to what I have. Also check out "Off Grid Dreaming", a fellow aussie playing with Lithiums, HBPowerwall (guy runs a forum, and has an enormous setup using 18650 laptop cells), and "One Up The Sleeve Customs" a guy playing with a 190aH set of lead acids, and getting rather good results from them. Soon I'll be joining the youtube crowd, and my id is dash8brj. Worked out the basics of the go pro, enough to use it for making the battery. I'll have the DSLR rolling as well, as it has better audio than the Go Pro (go pro, why oh why is your audio so shit without an external mic!)
Cabulture (Nth Brisbane) based very cheap panels.
So, I just made a snap purchase of something interesting.
I've got an unusual case where I want to take my 24V LTO battery pack out camping (to run an engel). To charge it from the car I'll need a 10 amp CC/CV boost converter, I was able to get one for $10ish. Charging it from solar gets a little tricker.
I did buy a smaller CC/CV boost converter so that I could wind down the current and stay within the capabilities of the solar panel, but it was going to be a bit of a cludge. I then happened to stumble on to these: MPT-7210A
These are a legit MPPT solar controller with step-up output, so can charge a higher voltage battery from a lower voltage solar cell; 12-60V input and 24-72V output. The tracking algorithm is the constant supply voltage method (which is effective but requires configuration) but apparently the tuning responsiveness is a bit ordinary and it struggles with rapid changes due to clouds etc. Apparently they can also switch to a fixed DC-DC boost converter mode but some people had problems with that.
Should arrive next week and I'm keen to give it a go.
ah yes, one of these. seen quite a few videos on them.
cooling mods and what not often required.
and plenty more to find if you take the time.
there are improvements and mods you can do to improve the base unit if required.
hmmmmm could be useful indeed.
Reading the description, it's not clear that it manages voltage hysteresis. As soon as the load drops off, voltage will recover and then the device may switch back on. It could chatter / cycle badly.
Read the instructions further down the page.
You can set disconnect and reconnect voltage.
Awesome. Sorry, I only read halfway down - the first set of instructions only had a single threshold.
for those looking for second hand batteries in Brisbane.
So, I had a go at the MPT-7210A, it works but has a number of issues:
1) It can store multiple config sets but if it loses supply power (like in clouds) it will reset to profile 0, so that profile needs to be safe
2) When the input voltage is low (like connecting it to a PSU instead of a solar panel), the tracking algorithm continues to increase current despite low voltage. Combined with #1 this could be risk if connected to a car accessory outlet.
3) It managed to overload a 10A PSU by drawing only 3A average, I think it needs more input filtering.
#1 and #2 means I'll have to change my plans about using this in DC-DC mode to charge my battery from a car. That said, it's not too hard or expensive to use a separate CC/CV boost converter.
Also just received a 200W flexible panel today so will have a go at that on the weekend.
OK.... so the 200W flexible solar panel turned out to be 100W. Was a perfect bright sunny day here and I got max power at around 18V & 5.3 amps, versus the 11 amps rated.
I want to keep it, just trying to arrange a discount. That said, at $120 it's not too bad a price for 100W.
Out of curiosity, where did you get the flexible solar panel - theres heaps on ebay touting different wattages etc. I know the ETFE ones are the better ones, but they're more pricey.
A small insignificant update, I finally mounted up my LCD display into a frame so it can sit on my desk.
Just need to velcro the pi to the back and add some zip ties to the cables to make it neat.
Yeah was an ebay special flexible panel. Cant remember the brand sorry, but in retrospect there were heaps of other comments against that seller complaining about dud/overrated panels.
I went out camping on the weekend and tried the solar for one arvo, the battery was already full so I didn't get to push the real wattage. I didn't consider the size well enough before I bought it, it's about 10cm too long to fit in the Ute which is a real pain. Slight shorter, or a folding panel and I could slot it in with against other similar sized camping gear. Tempted to leave it for use on a caravan and go to a more sturdy folding panel when I'm camping out of a ute.
On the bright side, my 12 cell 40Ah LTO pack (1.1kWh) has run a 40L Engel fridge for nearly two days without recharge. It started at 30V (2.5V per cell) on Saturday sunset, when I left for work Monday morning it was 27.3V (2.27V per cell) so only slightly below rated voltage. I feel like doing a Kramer and pushing it till it's empty just to see how far I can get with it
Yeah its amazing what these non lead things can do. I didn't pay much attention to my screen (had the little things backlight off), and one of the solar cables had come loose from the charge controller. My radios have been on all this time (about 3 weeks) and the battery was still 3.217v per cell. Mind you it would take quite a while for them to draw down a 2.1kwh pack at ~1A.
LTO Battery Update - been running the Engel about 60 hours this (Tuesday) morning, 26.2V (2.18V per cell) so still plenty of juice. Going to continue to push it just to see, but realistically if I can get two nights camping that would deal with the vast majority of scenarios.
is that with the aid of the flexible panel?
Nope, no solar at all.
I had the solar running from midday until sunset Saturday, and the battery was at my max allowable level when it stopped. Since then it's had 60 hours with no other charge. Technically full would be 2.8V/cell = 33.6V but the Engel can only cope with 30V, it maybe started at 80% full.
I've got the Engel low voltage cutoff set to 21.6V (I think) so 1.8V per cell, not completely flat but very little capacity remaining.
I can't imagine you'd want to do that often though, full cycles eek
These LTO's *should* have 30,000 cycle capacity and no major issue with high DoD cycles. Hoping that pans out to be true.
Edit - just checked, the Engel low voltage cutoff is configurable at either 21V or 23.1V. I have it set on 21V, or 1.75 per cell. Still above the 1.5V battery limit as long as they are balanced.
The other setting at 23.1V would be 1.92V per cell. Still pretty reasonable and would be in the last 5 - 10% battery capacity anyway. I might switch it to that when I get home.