MC4 Connectors SUCK for off-grid systems!!!

[SunEagle]

thanks for your advice. to answer the questions...

-no i can't get any specs on the panels that are there already. they are in a very remote location, and they are bolted down with security bolts.

-when i originally installed the system I put a charge controller there. it has been removed.

-i might be able to get specs on the 160 watt panels I'm adding, but you should try communicating with people in Haiti and asking them to go to the store and take a picture of the label on the back of a panel. the bottom line is I'm not going to know for sure exactly what I have until I get there.

-i am wary of putting a PWM controller on one sub array and MPPT on the other. I think they will fight each other. as you know the battery voltage is affected by the charge rate. if one subarray decides to taper the charge, it will affect the system voltage and the other controller will react. I'm worried they will be in constant battle. that is why i wanted to wire these two sub arrays in parallel and get a high amperage controller to handle it all.

and now i'm running out of time to figure this out!

Whatever panel arrangement you come up with you still need about 135amps to charge that 1350Ah 12V battery system. The 90 amps you think you can get is still not enough.

If you have a 16.2kwh system you need to be able to generate 3 times that amount in 4 to 5 hours because people will just use as much power as they can. So that requires about a 10kw worth of panels. Good luck building that with 50watt panels.

[garybeck]

Whatever panel arrangement you come up with you still need about 135amps to charge that 1350Ah 12V battery system. The 90 amps you think you can get is still not enough.

If you have a 16.2kwh system you need to be able to generate 3 times that amount in 4 to 5 hours because people will just use as much power as they can. So that requires about a 10kw worth of panels. Good luck building that with 50watt panels.

Im going to have to disagree with you on that. the battery bank is just for storage, and you can't have too much storage, the array is what is sized to the load. the array size is properly sized for the load. i've done a load estimate, is about 3500 watt-hours per day. when you account for battery efficiency, and modules being rated at standard test conditions, I need to create about 5000 watt hours per day. the 940 watt array will create almost year round in Haiti, with ~5 peak sun hours per day. the battery size is based on days of autonomy and maximum depth of discharge. with 4 days of autonomy and 80% maximum depth of discharge, a battery bank of 16.5 KWH is called for. so my 16.2 is just about right. anything smaller would be too small.

with all due respect, I disagree with your method of calculating. you don't size the array by the size of the batteries. everything is sized from the loads. there has to be at least 4 days of storage in the batteries, based on the average daily load. or it is too small. if your battery bank can be charged up in 4 to 5 hours, it is too small. they don't need 10KW of panels just because the battery is a certain size. the array size is based on the load and so is the battery. I put another system in a different area of haiti 2 years ago and it is operating flawlessly and part of that is because I put 5 days of storage in the battery bank and a maximum depth of discharge on 80%. but i would do the same in the US.

your point is well taken that they could just drain the battery anyway and it would be nice to have more solar. but if that were the case then I would want to add more batteries. but I worked with them extensively on the load calcluations and that is where it all starts. they will be using 3500 watt hours per day and that's what we're designing the system around. on rare occasions when they need more they will have a generator.

no offense, and I appreciate your input.

-gary

[PNW_Steve]

Im going to have to disagree with you on that. the battery bank is just for storage, and you can't have too much storage, the array is what is sized to the load. the array size is properly sized for the load. i've done a load estimate, is about 3500 watt-hours per day. when you account for battery efficiency, and modules being rated at standard test conditions, I need to create about 5000 watt hours per day. the 940 watt array will create almost year round in Haiti, with ~5 peak sun hours per day. the battery size is based on days of autonomy and maximum depth of discharge. with 4 days of autonomy and 80% maximum depth of discharge, a battery bank of 16.5 KWH is called for. so my 16.2 is just about right. anything smaller would be too small.

with all due respect, I disagree with your method of calculating. you don't size the array by the size of the batteries. everything is sized from the loads. there has to be at least 4 days of storage in the batteries, based on the average daily load. or it is too small. if your battery bank can be charged up in 4 to 5 hours, it is too small. they don't need 10KW of panels just because the battery is a certain size. the array size is based on the load and so is the battery. I put another system in a different area of haiti 2 years ago and it is operating flawlessly and part of that is because I put 5 days of storage in the battery bank and a maximum depth of discharge on 80%. but i would do the same in the US.

your point is well taken that they could just drain the battery anyway and it would be nice to have more solar. but if that were the case then I would want to add more batteries. but I worked with them extensively on the load calcluations and that is where it all starts. they will be using 3500 watt hours per day and that's what we're designing the system around. on rare occasions when they need more they will have a generator.

no offense, and I appreciate your input.

-gary

WOW! Thank you Gary!

I was under the impression that you needed to have the ability to charge your battery bank at C/10 or there about to prevent damage to your battery bank.

It looks like that a system with a 24v/370ah battery bank can be maintained with a 400 watt solar array as long as my loads are small enough to accommodate the array.

Thanks for straightening me out!!

[SunEagle]

Im going to have to disagree with you on that. the battery bank is just for storage, and you can't have too much storage, the array is what is sized to the load. the array size is properly sized for the load. i've done a load estimate, is about 3500 watt-hours per day. when you account for battery efficiency, and modules being rated at standard test conditions, I need to create about 5000 watt hours per day. the 940 watt array will create almost year round in Haiti, with ~5 peak sun hours per day. the battery size is based on days of autonomy and maximum depth of discharge. with 4 days of autonomy and 80% maximum depth of discharge, a battery bank of 16.5 KWH is called for. so my 16.2 is just about right. anything smaller would be too small.

with all due respect, I disagree with your method of calculating. you don't size the array by the size of the batteries. everything is sized from the loads. there has to be at least 4 days of storage in the batteries, based on the average daily load. or it is too small. if your battery bank can be charged up in 4 to 5 hours, it is too small. they don't need 10KW of panels just because the battery is a certain size. the array size is based on the load and so is the battery. I put another system in a different area of haiti 2 years ago and it is operating flawlessly and part of that is because I put 5 days of storage in the battery bank and a maximum depth of discharge on 80%. but i would do the same in the US.

your point is well taken that they could just drain the battery anyway and it would be nice to have more solar. but if that were the case then I would want to add more batteries. but I worked with them extensively on the load calcluations and that is where it all starts. they will be using 3500 watt hours per day and that's what we're designing the system around. on rare occasions when they need more they will have a generator.

no offense, and I appreciate your input.

-gary

It sounds like you built in the spare capacity you require for energy storage. It is sometimes hard to tell what someone has done unless they mention their daily watt hour requirements.

So I agree that you have enough energy for multiple days of usage which is great. What you haven't quite learned is that even if you only use 20% of the battery system per day you still need to provide enough amps to motivate the acid so it does not form sulfate on the battery plates. Unless you do this with enough solar wattage or a generator the batteries will slowly build up until you have lost some of it's storage capacity. After a while most people find that out because they get a few days of no sunlight which drains the batteries way down to the point of failure.

The reason for being able to charge up the bank in as few hours as possible is due to the potential of clouds or anything that blocks the useful sunlight. If you don't get back up to 100% SOC you start off with a smaller safety margin.

If you have been relying on minimal charging amps I at least hope someone has measured the specific gravity of those batteries so they know exactly what SOC they are.

[SunEagle]

WOW! Thank you Gary!

I was under the impression that you needed to have the ability to charge your battery bank at C/10 or there about to prevent damage to your battery bank.

It looks like that a system with a 24v/370ah battery bank can be maintained with a 400 watt solar array as long as my loads are small enough to accommodate the array.

Thanks for straightening me out!!

I would be cautious taking someone else's word that your battery system doesn't need at least a C/10 charge rate to stay healthy. You can use less amps to charge but I would expect your battery system not to last the cycles you expect them to.

[Mike90250]

.....
-i am wary of putting a PWM controller on one sub array and MPPT on the other. I think they will fight each other. as you know the battery voltage is affected by the charge rate. if one subarray decides to taper the charge, it will affect the system voltage and the other controller will react. I'm worried they will be in constant battle. that is why i wanted to wire these two sub arrays in parallel and get a high amperage controller to handle it all.........

Worry no longer. As long as multiple controllers are set pretty close to the same battery type/voltage, they will not "fight" or conflict.

Your larger problem is the one of the old controller having grown feet and disappeared. You won't be happy if your Midnight classic wanders off too.

[Sunking]

Im going to have to disagree with you on that. the battery bank is just for storage

You have made so many mistakes, it is too late to help you. Once you loose a lot of money doing it incorrectly, you wil learn the hard way.

Here are some things you will learn loosing a lot of money.

Run as high of a battery voltage as possible. At your current panel wattage 24 volts would have saved you a lot of money.
Batteries require minimum charge current, that is why manufactures warn you.

Good luck and start saving your money to do it right the second time.

[PNW_Steve]

I would be cautious taking someone else's word that your battery system doesn't need at least a C/10 charge rate to stay healthy. You can use less amps to charge but I would expect your battery system not to last the cycles you expect them to.

Thanks SunEagle,

While I am a newbie, I have learned a bit from the great stickies and various discussions. My reply to Gary was a poor attempt at being humourus.

[garybeck]

So I agree that you have enough energy for multiple days of usage which is great. What you haven't quite learned is that even if you only use 20% of the battery system per day you still need to provide enough amps to motivate the acid so it does not form sulfate on the battery plates. Unless you do this with enough solar wattage or a generator the batteries will slowly build up until you have lost some of it's storage capacity.

charging 20% per day and using 20% per day is about right. IMO the charge rate you suggested is too fast and will not provide any days of autonomy for cloudy days.

the basic battery formula i use is: WH/day consumption X days of autonomy / max depth of discharge
if days of autonomy = 5 and max DOD = 80%, if you are down at the max DOD, yes it will take 5 days to recharge.
this is a properly sized battery bank. if your battery bank is only double your average daily use, you will cycle too deeply every day and decrease the lifetime of your batteries.

you are correct about sulfation being an issue but this is prevented with battery equalization, not by improper oversizing the array.

[garybeck]

You have made so many mistakes, it is too late to help you. Once you loose a lot of money doing it incorrectly, you wil learn the hard way.

Here are some things you will learn loosing a lot of money.

Run as high of a battery voltage as possible. At your current panel wattage 24 volts would have saved you a lot of money.
Batteries require minimum charge current, that is why manufactures warn you.

Good luck and start saving your money to do it right the second time.

wow, i didn't know this forum was here for being rude and insulting.

FYI, i've been doing this for over 30 years. I've designed thousands of systems that are out there in the world working right now. I typically get 8+ years out of my golf cart batteries the way i design systems.

the forumulas I use for designing offgrid battery banks, i didn't make them up. they were taught to me when I went to school to learn about photovoltaics long before this forum existed. they still work.

if you disagree with something i said, then I'm all ears. but if you are going to be disrespectful, I have better things to do with my time. I'm going to Haiti to help some people. I don't have time to waste being insulted. but hey, if it makes you feel good to talk down to people, have fun with that.

yes 24V is better in most cases, but there is more to the story. the reason it is 12 V battery is because they already have a 12V inverter. this is an upgrade to an existing system. I don't need to "learn by losing a lot of money" that 24 V is better.

have a nice day. and happy holidays.

[Sunking]

FYI, i've been doing this for over 30 years.

And it certainly shows. You have not learned anything since then using antiquated techniques and equipment. 30 years ago they only had low voltage panels used in parallel, analog controllers, parallel batteries out of ignorance, and the only batteries available back then that were suitable were golf cart batteries. Sounds like you still use 8-Track tapes. I have a lot more mileage and years ahead ahead of you. Difference is I stayed up with technology as it is required to have a PE and stay in biz.

[garybeck]

And it certainly shows. You have not learned anything since then using antiquated techniques and equipment. 30 years ago they only had low voltage panels used in parallel, analog controllers, parallel batteries out of ignorance, and the only batteries available back then that were suitable were golf cart batteries. Sounds like you still use 8-Track tapes. I have a lot more mileage and years ahead ahead of you. Difference is I stayed up with technology as it is required to have a PE and stay in biz.

people who run discussion forums should be more respectful. most discussion forums have rules, where you are supposed to be respectful. if the person running the forum doesn't know what that means, geeze...

for the record, my formulas are not ancient as you suggest. if you go on to the AltE website they have formulas that reflect exactly what I laid out. you start with the daily load, you multiply by the days of autonomy and the maximum depth of discharge. I just played with their calculator and it suggested a larger battery bank than I have (not smaller as suggested here) and the exact same 900 watt array that I have in my design.


maybe you should contact them and talk down to them and tell them how their calculator is wrong.

you are not taking into account, this system is in haiti. golf cart batteries are still the only thing I can get there. and for the money, in terms of dollars per amp hour, they are still hard to beat even here. i have to go 12 V because they have a 12V inverter and no money to buy a new one. these people have nothing. no running water, no electricity. I'm going to help them with the materials they have available. I don't have time to waste, being talked down to by a PE who might know more about electronics than I do but has a thing or two to learn about respect. there was absolutely no reason to be disrespectful or to talk down to me.

congrats on your PE, though.

[Mike90250]

.....you are correct about sulfation being an issue but this is prevented with battery equalization, not by improper oversizing the array.....

So, I'm a gonna step in here and make a couple comments.

1) altestore calculator I don't even have to see it, to know it's sole purpose is to sell gear, not the best system. ( I did look at it, and it's grossly undersized my array for my area, it's way too general - one size fits none. It's a starting point, but needs refinement )

2) Sulfation starts off as soft & reversible, but as hours progress, it sets harder and harder and diminishes battery capacity as more and more sulfur gets locked into the crystals. Most high end controllers have a 30 day EQ timer built in. However, after 48 hours, the sulfation crystals are pretty hard and the process to reverse that becomes exceedingly difficult. Waiting 30 days is simply walking your battery capacity down to failure levels. If you are stuck in the 70's mindset, PV costs way more than batteries, so the trade-off worked then. With PV being as cheap as it is now, you can properly size your array to allow daily recharge and prevent sulfation. EQ is an overcharge condition that will "re-balance" the cells in the bank so they are all at 100% and it can remedy slight sulfation, at the cost of positive plate corrosion. So you end up dancing on a razor - death by corrosion or death by sulfation. Most banks die from sulfation caused by undercharge. EQ is supposed to only be done when the SG in the cells begins to vary, not as an automatic routine.

3) Sunnking is a rough coarse fella, and cares about electronics, not about feelings. Nearly all the time he's right, and that's the ultimate goal here, not mollycoddling adults.

[PNjunction]

Ok, if you're going to do the 12v thing, and hate the MC4-s, then you may want to use Anderson "Power Pole" connectors. They come in a variety of current handling capabilities, and need a special crimper. Popular for 12v amateur radio use.

https://en.wikipedia.org/wiki/Anderson_Powerpole

If you stick to a standard, then you or your users won't have to worry about cross polarity and the like. From the wiki, at the top, one standard to follow when looking INTO the connectors, is "Red on the left, Black on the right". Connector surface facing down, or on the bottom of the connector.

Makes a supposedly airtight-seal when crimped properly, although some have been known to lightly tin the cable ends too.

[Sunking]

for the record, my formulas are not ancient as you suggest. if you go on to the AltE website they have formulas that reflect exactly what I laid out.

Yes we know Any here and ran her off. As Mike points out they are about sales, not operations. There calculations come out with grossly undersized equipment to make a sale. Nothing more complicated than than Bait and Switch.

I understand poor people have poor ways and places like Haiti have no codes or ethics. That is not the case in the USA and piss-poor ways will not cut it here. There is a good reason they let me hang around here. I am a professional engineer, and like a doctor, I will not allow anyone to condone smoking or drinking in my presence. If you take offense to that, then grow some skin.