Solar charge controller, what for?

[bungawalbyn]

Hi Karrak
The cables are pretty heavy on the battery to inverter out, a little less from Panels to same, and less still to meter etc bus bars.

Nothing is getting warm.

The 300amp circuit breaker is backed up by a 400amp T class fuse that's supposed to break 20x faster and interrupt 100,000 amps. (Not in photo)

As for panel disconnect There is the high voltage cut off 150 amp relay, operated by the hi V sensor. A manual contactor on both + &- circuits and a 400amp manetic latching contactor on the battery in + , operated by the battery monitor to cut for both hi & lo V.
Is this insufficient?

As to the voltage loss from meter bus bar to battery terminals, if an easy fix is not available, then it's easy enough to get an idea of how that behaves and adjust settings accordingly. Fortunately the drop, in it's effect on safety in charge /discharge, actually brings the settings back from the extremes.

[karrak]

Hi Karrak , You've got all that right except the board on the right is a cell monitor not a balancer.
I figured putting the sensors on a more direct line would reduce/ alleviate the Vdrop but I wanted all drain to come after LV cutout contactor. The cheap circuit breaker is rated at 300amps. I have to recheck, but this component may be part of the VDrop problem.

Hi Bungawalbyn,

It is a little difficult to see from the pictures but I think the size of the cable you are using is too small for the current you are putting through it. Here is a simple online calculator to calculate your voltage losses. http://www.calculator.net/voltage-dr...res=1&x=89&y=9

Regarding cable size, the fuses/circuit breakers take time to break, your cable and connectors may have to cope with the full short circuit current that the battery will supply until this happens. I would think your 1000Ah battery could supply maybe up to 10,000 amps if shorted. If it takes 0.1 of a second before your fuse/circuit breaks your cable has to dissipate a huge amount of power without melting. This make cable sizing a tricky subject and subject of much discussion. An absolute bare minimum should be large enough to safely continuously carry the current the safety device is rated at, in your case at least 300A.

Most good quality fuses/circuit breakers will specify a maximum current that they will safely cope with, for fuses this is called the burst current. If you put more current through the device than this specification in might explode or not disconnect the load in a timely manner. Just something to think about.

I am a little concerned that you seem to only have one panel disconnect relay. If this relay fails closed you could quickly damage your battery.

If you are concerned about the monitoring electronics drawing power after the LVD relay had disconnected the load you could put a small disconnect relay in the separate circuit.

I hope I am not appearing to be too negative about your efforts. I think you are on the right track but there some things that I think could be improved or need to be thought about.

Simon

[bungawalbyn]

The usual approach to getting around these problems is to have separate wiring directly from the battery terminals to all the monitoring circuitry, volt meters etc. so you are not reading the voltage drops in the cabling as well.

Is the relay at the bottom on the back the LV disconnect relay and the relay towards the top on the left the PV disconnect relay?

What is the PCB on the right in the middle of the front, is it a cell balancing board?

What is the rating of the cheap circuit breaker on the front bottom left hand side?

A circuit diagram would be useful.

Simon

Hi Karrak , You've got all that right except the board on the right is a cell monitor not a balancer.

I figured putting the sensors on a more direct line would reduce/ alleviate the Vdrop but I wanted all drain to come after LV cutout contactor. The cheap circuit breaker is rated at 300amps. I have to recheck, but this component may be part of the VDrop problem.

So far I only have half my panels hooked up to it, when charging at max amps, 35, the difference . 0.25V less at battery terminals than bus bars. If this is still the case when I attach the rest of the panels I may not bother with it and just adjust the cut off/on points on the controllers. As it stands it just makes those points more conservative.
I've been away a bit the last couple of days so I'm still to see it operate over a full day cycle.

I've left half of the old system functioning while I put the new setup through it's paces. It's interesting to compare the 2. Old system MPPT controller on FLA does squeeze a couple of amps extra early and late, but at peak sun it's back down to absorb/float and pulsing around 5 to 10 amps while the LFPs just keep on sucking up the 35amps. This is exactly why I've chosen to go LFP


PNJ, I cleaned all the cable lugs and other contacts, everything is soldered, If I can't find a particular component, I can live with it.

Early days, but it's all going well.

[karrak]

So far the only problem showing itself is a voltage drop at the sensor etc bus bars compared to the battery terminals. Higher when charging, lower when discharging. Obviously some drop across components. Messes up the cell voltmeter a bit as cells 1 & 4 read the difference between bus bar and adjacent cell.

The usual approach to getting around these problems is to have separate wiring directly from the battery terminals to all the monitoring circuitry, volt meters etc. so you are not reading the voltage drops in the cabling as well.

Is the relay at the bottom on the back the LV disconnect relay and the relay towards the top on the left the PV disconnect relay?

What is the PCB on the right in the middle of the front, is it a cell balancing board?

What is the rating of the cheap circuit breaker on the front bottom left hand side?

A circuit diagram would be useful.

Simon

[PNjunction]

I've noticed that also when measuring directly across cell terminal aluminum knuts, or directly across the bus bar bolt heads vs at the end or middle of a bus bar.

Something like the difference between say 3.55v across the cell terminals, and 3.56v on the bus bars themselves. Close enough for my work.

However, one thing I do recommend is upon receiving these cells is to lightly hit up the terminal connection points with a bit of scotchbrite pad to remove oxidation, and perhaps a *light* coating of noalox or penetrox. Inspect the bus bars too and give them a light scrub where you are going to make the connection. My bus bars are nickel based, and even though they looked clean, a bit of oxidation did come off. If you use a wire brush, do so lightly instead of scrubbing it hard - since that may tend to imbed steel into the aluminum. Always check the terminal screw holes to make sure no junk falls inside there either.

Still, I do notice slight differences at the bus bars - it all depends on how tight in spec you need to be. Remember that we are sometimes making several dissimilar metallic connections, like aluminum to nickel to steel to copper wire. Good to keep an eye on it all like you are doing.

One great thing about your cells is that they have multiple cell terminal connections for very high amperage use. But even if you are doing the solar "Sub-C" thing, having an extra set of bus bars in parallel would be cool to have connected up anyway to reduce resistance connections even further down.

[bungawalbyn]

Glad nothing at your end went bang. But my concern, is your equipment really safe and will nothing be sent down the line from your home if the grid goes down? Unless you have a factory made UL listed isolation device that keeps power on your property there is always the chance of something failing for the wrong reasons with dangerous results.

Hey guys, read the thread. I'm nowhere near the grid. I think maybe you've been led astray by PNJ's warnings to the "Lurkers"

So far the only problem showing itself is a voltage drop at the sensor etc bus bars compared to the battery terminals. Higher when charging, lower when discharging. Obviously some drop across components. Messes up the cell voltmeter a bit as cells 1 & 4 read the difference between bus bar and adjacent cell.
Once I get a chance to go over it all while operating I'll find the culprit if it is just one component, if it's accumulative, I may have to reroute some stuff, or get a good handle on the differences at various charge values and learn to live with it.
After all meters etc are only there to indicate what's going on in the system. Absolute values are somewhat unnecessary when familiar with it's operation as it is movement in voltage, proportionality, ie rapid increase or rapid decline, as the batteries approach the "Knee" that is the thing we are looking for and trying to avoid. A clock set on the wrong time, still accurately measures the passage of time.

If one gets an accurate reading, does that mean it's a Fluke?

[J.P.M.]

Nothing went bang!

Yet.

[SunEagle]

Nothing went bang!

Glad nothing at your end went bang. But my concern, is your equipment really safe and will nothing be sent down the line from your home if the grid goes down? Unless you have a factory made UL listed isolation device that keeps power on your property there is always the chance of something failing for the wrong reasons with dangerous results.

[bungawalbyn]

Nothing went bang!

[PNjunction]

I still have to integrate the HWS dump relay into the house wiring so that part of the controls is inactive.

Standard warning here for lurkers - if this is a grid-tie inverter connection it may be illegal depending on your location. I'm sure the Op has done his due diligence in this arena.

From my OWN safety standpoint, even though this is illegal where I live, I'm not counting on it during an outage. Aside from line workers getting zapped, I personally don't want to encounter this from the guy down the street who just doesn't know.

So, when there is an outage in my area, I don't make ANY assumptions that my lines are not hot, or that they will not become hot from a guy down the street later on!

Anyway, congrats on your system so far. From what I've seen, it looks like you are playing it safe.

[bungawalbyn]

How about that, it works.
It charges anyway.
Yet to have it go anywhere near hi or low.
I still have to integrate the HWS dump relay into the house wiring so that part of the controls is inactive.
I only have half my panels hooked up to it at present, It charged at 30 amps at 13.6V for a couple of hours then dropped back as the sun went off the panels.
I'm using them now to power the house, voltage is 13.26 under a light load. All cells identical

There is a bit of a voltage drop between the meters and the battery terminals. Something to think about.

[bungawalbyn]

OK guys

Here is the board. The relay hanging over the front of the board is a 12v to 240Ac to switch on and off HWS as load dump.

It's a little Prof Ratbaggy but I kind of like that aesthetic.

Oh and don't freak out about the crappy circuit breaker, I have a 400A t class fuse between it and the battery.

All the relays and voltage sensors have been bench tested and are working to plan. I haven't figured out a way to run the BMS and cell meter/alarm through their paces without hooking it up to the battery. Though meter/alarm has been checked pin by pin and does what it should. It will need adjustment when hooked up. Default alarm setting is a little high. (Designed for LiPo's but has suitable range with adjustment.)

I just have to make a cover for the BMS and alarm and a frame to hang it in. Make up the cell to sensor loom and it's ready to install

Inverter cables will be attached to PV side of battery cut offs on the contactor terminals

[PNjunction]

Thanks for your concern. I'm mindful of the dangers and risks.

I suspected so, but know there are lurkers who may tend to rush into things. Like the general rule about voltages and cabling ...

For every 1000 watts of AC, add 12v. Ie, if you go beyond 1000 watts of load, you should build a 24v system instead and so forth.

PEER REVIEW request: is the statement above basically for lead acid and peukert concerns? Hmmm....

I'm actually excited to see this baby in action, but don't let me push you - take your time...

[SunEagle]

Thanks for your concern. I'm mindful of the dangers and risks.

I'm not a total noob. This is my third solar system, + I've upgraded one of my neighbours systems. I'm used to handling dangerous items. Tractors, Chainsaws, Power tools, motorbikes, GF and the like. I built and wired my house without drama.

Safety is one of the reasons I stick to 12V. You can still get a reasonable tingle off 12V panels in good sun, and I know DC is more dangerous than AC

I'm bench testing everything before going live.

But of course it's normally the thing you don't see that bites, and that's why I'm here mainly. While not a noob I know I am no expert, so keep the advice coming and hopefully we will avoid any mistakes.

A bit of chilli gives the stew a lift.

Just don't put too much of that Dave's Insanity Hot sauce in the Chili.

[bungawalbyn]

Thanks for your concern. I'm mindful of the dangers and risks.

I'm not a total noob. This is my third solar system, + I've upgraded one of my neighbours systems. I'm used to handling dangerous items. Tractors, Chainsaws, Power tools, motorbikes, GF and the like. I built and wired my house without drama.

Safety is one of the reasons I stick to 12V. You can still get a reasonable tingle off 12V panels in good sun, and I know DC is more dangerous than AC

I'm bench testing everything before going live.

But of course it's normally the thing you don't see that bites, and that's why I'm here mainly. While not a noob I know I am no expert, so keep the advice coming and hopefully we will avoid any mistakes.

A bit of chilli gives the stew a lift.