Li-thiiii-um.... continued.

[Vermilye]

Originally Posted by BobG

8 AWG would be fine for circuit from the MPPT to the busbars. According to BlueSeas it results in less than 1% voltage drop. The panels will very seldom if ever put out 30 amps laying flat.

And your output voltage with lithium batteries will rarely be as low as 12V. I've managed to hit 38 amps with 640 watts worth of panels, all aimed at the sun on a clear winter day in Quartzsite (521 watts peak on the Victron 100/50). With 360 watts you will be lucky to hit 25 amps.

[Brian B-P]

Originally Posted by John in Santa Cruz

so 360 watt solar, could be as high as 30A charging... for the foot or so long wires from the MPPT to the main + and - terminal strips, should I use AWG 6 or 8?

The first table of resistance by wire gauge that I found listed

• 0.3951 ohms/1000ft for 6 AWG, so 0.8 milliohms for the two-foot round trip, or 24 mV voltage drop at 30 amps (0.2% of 12 V), dissipating 0.72 W
• 0.6282 ohms/1000ft for 8 AWG, so 1.3 milliohms for the two-foot round trip, or 39 mV voltage drop at 30 amps (0.3% of 12 V), dissipating 1.2 W

(... if I didn't make a silly math error)
Although the smaller gauge has much more resistance than the larger gauge, I think it's just too short a distance and too low a current for it to matter. It would be another matter over the whole length of the trailer or for hundreds of amps.

[John in Santa Cruz]

oh well, the coil of awg 6 was on top, wires cut to length and 3/8-6 eye connectors crimped.

[John in Santa Cruz]

so while I'm not going to try and fix that drawing I pasted a page ago, I decided to put each battery on its OWN 100A fuse as these SOK batteries have a 100A maximum drain, so if I ever want over 1200-1400 watts of Inverter or whatever, I can pull up to 200A total from the two of them.

[Brian B-P]

Originally Posted by John in Santa Cruz

so while I'm not going to try and fix that drawing I pasted a page ago, I decided to put each battery on its OWN 100A fuse as these SOK batteries have a 100A maximum drain, so if I ever want over 1200-1400 watts of Inverter or whatever, I can pull up to 200A total from the two of them.

If the battery has an internal BMS that disconnects on high current, you don't need to duplicate that externally to protect the battery; however, if individual fuses let you move the fuse location closer to each battery, that would be a good thing.

[John in Santa Cruz]

I couldn't find any inline 100A fuses that were suitable for mounting directly on the battery terminals, so these will be at the end of about 1 foot of AWG 4 each. c'est la vie.

[BobG]

John, I did not look up the SOK terminal to see if these would work but here are some good battery terminal fuses. I'm thinking you will probably be able to tell by a glance at them



https://www.bluesea.com/search/results/battery%20fuse

[Brian B-P]

Originally Posted by John in Santa Cruz

I couldn't find any inline 100A fuses that were suitable for mounting directly on the battery terminals, so these will be at the end of about 1 foot of AWG 4 each. c'est la vie.

That's still pretty good.

Originally Posted by BobG

John, I did not look up the SOK terminal to see if these would work but here are some good battery terminal fuses. I'm thinking you will probably be able to tell by a glance at them

https://www.bluesea.com/search/results/battery%20fuse

This is exactly what those Marine Rated Battery Fuses (MRBF) are for, but there have been intense debates in this forum about whether the current-interrupting capacity of this type of fuse is adequate... although for both the MRBF type and the ANL type (which John is using) Blue Sea Systems notes "High Interrupt Rating satisfies ABYC requirements for DC main circuit protection on large battery banks" (that rating is 6,000 amps for the ANL type according to Blue Sea).

[Mike Lewis]

Originally Posted by Brian B-P

This is exactly what those Marine Rated Battery Fuses (MRBF) are for

Thanks for letting us know what MRBF stands for; I had wondered. Now maybe I'll stop garbling that acronym.

[BobG]

John, whichever type fuse you get; ANL or the battery terminal fuse, you might want to carry a spare or two.

[John in Santa Cruz]

Originally Posted by BobG

John, whichever type fuse you get; ANL or the battery terminal fuse, you might want to carry a spare or two.

I actually have two spare 100A fuses as each one came with a extra, so... yeah, I'll toss those in the top drawer

[John in Santa Cruz]

so i left the fan and a few lights on for a couple days, a couple amp load, with the solar panel disconnected and converter switched off... ran the battery down to maybe 90%, then shut the load off, and switched the PD4655Li back on (if you look close at the red line on the far left edge of this graph, you can see the load as negative 2 amps or so, then a tiny bit of 0, then blam, 40 amps or so of charging...

this is the graph from the smartshunt shortly after it finished charging... this is JUST the battery current/voltage.



after its fully charged, at 0 amps and 14.6V, those spikes are odd. that's about 90 minutes total on the graph. its like the battery is suddenly drawing 12-20 amps for a few minutes every 20 mins or so?

the voltage drop under high current is due to the inadequate factory wiring, I will be replacing it with AWG4, which should help a lot, as well as using a beefier disconnect switch, etc as i've outlined above.

[BobG]

John, could it be that the BMS shut the charging off at 14.6 volts? The current then dropped from 11.6 to 0 amps. As the battery sat for a while the voltage dropped below 14.6 volts and the BMS allowed charging to continue?


Try lowerring the charger bulk or absorption current to slightly less than 14.6 volts. Maybe 14.4 volts and see what happens.

[John in Santa Cruz]

ahhhh. CurrentConnected (SOK distributor/reseller) answered my rather detailed request via their site... tl;dr, its the BMS balancing the cells, and it will stop after a short while.

Hi John,

Thanks for the detailed message, you provided everything we needed to help with your issue, so thank you so much for that!

What you are seeing is the BMS balancing the cells inside. When the current drops down just about vertically on your graph, this is the BMS briefly interrupting charging. While this has happened, it is working internally to balance out the cells, but this can take some time. The battery is about 99% charged at this point. Once the BMS has gotten the cells perfectly balanced, these spikes will cease to take place. This is only happening like this because the battery is brand new and it has not yet had time for the BMS to balance everything out.

After this initial charge you did, the BMS will get the cells all balanced, and from there they will stay balanced, so you will see this practically never happening after the initial balance has taken place. This is nothing to worry about and is not a fault with the batteries or charger. I don’t think the undersized wire is any issue because as the current drops, the voltage drop on the wire also decreases so the batteries can still get a full charge.

Great job on the install and thank you for the detailed email. Let me know if you have any further questions!

[BobG]

Ah, the BMS is balancing the cells. That is good to know.

[John in Santa Cruz]

yeah, I did another partial discharge, then recharge cycle, and it only did two rebalances then went quiet.

I do think I'm going to need to put some 12V DC regulators on the lighting circuits as the unregulated main ceiling lights pulse and flicker a bit on either the PD4655 or the battery. I've got a couple that are 6A, and output a filtered 12.0V DC for an input from 9-18VDC input, thats enough to run the lights, but I think the ceiling fan is on one lighting circuit, and the stove hood fan is on the other :-/

[splitting_lanes]

Originally Posted by John in Santa Cruz

yeah, I did another partial discharge, then recharge cycle, and it only did two rebalances then went quiet.

I do think I'm going to need to put some 12V DC regulators on the lighting circuits as the unregulated main ceiling lights pulse and flicker a bit on either the PD4655 or the battery. I've got a couple that are 6A, and output a filtered 12.0V DC for an input from 9-18VDC input, thats enough to run the lights, but I think the ceiling fan is on one lighting circuit, and the stove hood fan is on the other :-/

Is the flickering of the lights occurring during a charge cycle?

These batteries aren’t that much higher voltage than FLA or AGM, it’s surprising how many people report light and/or fan issues after switching to LFP. LED lights shouldn’t be very voltage sensitive, as they output light from current, I guess it’s the circuit that’s limiting current struggling with higher voltage?

[John in Santa Cruz]

Unregulated LED just have series resistance to limit the current, so the brightness is directly proportional to the voltage... Regulated LED have an active current regulator chip so the are constant brightness.

[oldwave]

Outside of the fan, could you replace the bulbs in the fixtures with regulated bulbs, I have seen some of them?

[John in Santa Cruz]

Originally Posted by oldwave

Outside of the fan, could you replace the bulbs in the fixtures with regulated bulbs, I have seen some of them?

the corner captains lights, I put regulated bulbs in. I have not found any for the wedge base flat PCBA style bulbs in my overheads.

these aren't the original lamps, they are some warm-white ones I found on ebay, but same idea...



note I modded the upside down one by cutting away 6 of the 8 resistors... the black chip in the middle is a 'full wave bridge diode', which means they work no matter what polarity they are plugged in. each of the little chip resistors R1-R8 is in series with 3 of the LED chips, so by cutting out 6 of hte 8, I have reduced this light to 1/4th its original brightness. I did this to selective lights, so I could have nice evening lighting, or bright working light, depending on which ones I switch on.

these are a variety of different regulated floods I tried in the 'captains' reading lights...



I think I ended up using the middle row right lamp as having a good warm white color balance, and nice soft even light. the top row left one is what they came with. My wife likes a brighter reading light than I do, so the middle row left one is what ended up on her side of the dinette.