Here's the current situation: My mother has a 1440 W trolley inverter (Crystal Intellipower) with 2 X 105ah SLA batteries. This backs up a DSTV decoder and a smart TV (I haven't measured, but not larger than 40 inches) and maybe charging a not very modern cell phone with a micro USB charger connection. That's not a big load, and I suspect it is to her advantage. 

Anyway, this works quite well at Stage 4, but I wonder how long it will last. Currently it's 8 months old, and during that time she has had outages of 18 hours (inverter eventually shut down) and 15 hours (inverter stayed up and started recharging when the grid came back up). As I said, I think the small load has kept her in the game thus far. I still wonder if damage has been done (really, how much damage has been done) and how long this can last.

So I start thinking about a lithium replacement. I figure that one 200ah LI will do as good a job at least as two 105ah SLAs.

The inverter has no menu with options. It is designed for LA batteries, and the only choice is of charge current - 10A or 20A controlled by a switch.

But how good a job do the lithium drop ins do?

SLA is 12V. You can't get a 12V LI battery because the V per cell is over 3V. And the charging is quite different, especially in terms of voltages. 

So what happens? The LI drop ins have some sort of electronics. Is one of the functions of the electronics to make the LI battery look to the inverter like a LA battery, or to convert the charging current and voltage to something the LI cells can use? And when the battery is discharging, does the inverter get 12V from the >12 pack of cells?

Maybe I'm over-thinking this.
 

7 minutes ago, Bobster. said:

Maybe I'm over-thinking this.

Definitely 🙂

LiFePO4 12V batteries generally would have 4Showever manyP cells. For ease lets assume 200Ah battery uses 200Ah cells, so 4S1P configuration at 3.2V nominal you have 12.8V should be charged with 3.45V per cell or so, so 4 x 3.45 = 13.8V but could be ok all the way up to 4 x 3.6V = 14.4V, so if the trolley does not try and get the charge Voltage higher than this, you should be golden... as for the

11 minutes ago, Bobster. said:

The LI drop ins have some sort of electronics.

yes, its called a BMS 🙂 just like all other Lithium type batteries, ideally you'd want one with Bluetooth comms, since very few if any have any wired communication options, with the Bluetooth you can at least get an idea in the state if charge/balance of cells/health in general...

2 minutes ago, Kalahari Meerkat said:

yes, its called a BMS 🙂 just like all other Lithium type batteries, ideally you'd want one with Bluetooth comms, since very few if any have any wired communication options, with the Bluetooth you can at least get an idea in the state if charge/balance of cells/health in general...

Aha! That is interesting. A useful diagnostic tool beyond the 4 section LCD display on the inverter.

11 hours ago, Bobster. said:

. I figure that one 200ah LI will do as good a job at least as two 105ah SLAs.

Hmmmm... I don't want to give the impression that I'm an electrician, but this won't work safely unless I double up on cable thickness.

So it has to be two 100ah batteries and one of those pesky balancer wotchamacallits

1 hour ago, Bobster. said:

Hmmmm... I don't want to give the impression that I'm an electrician, but this won't work safely unless I double up on cable thickness.

ok, maybe, what is the average and peak draw? have you measured? what is running off the inverter and its consumption? how long did the SLAs run and down to what SOC? a 1440W trolley can draw 120A, I guess, so yebo yes, 50mm^2 cabling is probably called for... but... I suspect you never come even close to this amount of current draw... else the SLAs would have soiled their shorts in well less than 2 hours and been down to 0% SOC... surely...

Edited January 30, 20233 yr by Kalahari Meerkat

3 hours ago, Kalahari Meerkat said:

ok, maybe, what is the average and peak draw? have you measured? what is running off the inverter and its consumption? how long did the SLAs run and down to what SOC? a 1440W trolley can draw 120A, I guess, so yebo yes, 50mm^2 cabling is probably called for... but... I suspect you never come even close to this amount of current draw... else the SLAs would have soiled their shorts in well less than 2 hours and been down to 0% SOC... surely...

Perhaps the 1440W inverter is 24V in which case the current is only 60A max. Cable being a short run to the trolley housing the batteries. No ways that 2x50 sq mm is required. 

Edited January 30, 20233 yr by Scorp007

Thanks for the replies and the questions @Scorp007and @Kalahari Meerkat. I am fairly sure the inverter is 12V. As to the actual loads, I will do the arithmetic, but I need to be on site to do it.

I suspect that the inverter and SLAs are substantially underloaded.

20 hours ago, Kalahari Meerkat said:

ok, maybe, what is the average and peak draw? have you measured? what is running off the inverter and its consumption? how long did the SLAs run and down to what SOC? a 1440W trolley can draw 120A, I guess, so yebo yes, 50mm^2 cabling is probably called for... but... I suspect you never come even close to this amount of current draw... else the SLAs would have soiled their shorts in well less than 2 hours and been down to 0% SOC... surely...

OK... Today I popped in and looked at all the devices that are being backed up. Well... the markings aren't very helpful. EG there's a phone charger (old USB micro) that says the input is 0.1A at 100 to 240V. What? That can't be 50 watts, can it?* The TV did actually specify a number of watts - 74. The DSTV decoder runs off a brick power supply that is labelled in the same non-exact way as the phone charger.

My back of fag packet calculations came to 194W. 

I turned everything on, and the display on the inverter informed me that it was now providing 160VA. What's the difference between VA and W? (OK... most of what I know about electricity is DC).

Long and short: I don't think it's heavily loaded. By my calculations it should be good for 5 hours before SOC gets to 50%. So I think those batteries are not heavily loaded and that's going to turn out to be a good thing.



* I think the answer  is that it will draw 0.1A at 100V, and proportionately less current as the voltage increases. IE It's probably about 10W.

1 hour ago, Bobster. said:

OK... Today I popped in and looked at all the devices that are being backed up. Well... the markings aren't very helpful. EG there's a phone charger (old USB micro) that says the input is 0.1A at 100 to 240V. What? That can't be 50 watts, can it?* The TV did actually specify a number of watts - 74. The DSTV decoder runs off a brick power supply that is labelled in the same non-exact way as the phone charger.

My back of fag packet calculations came to 194W. 

I turned everything on, and the display on the inverter informed me that it was now providing 160VA. What's the difference between VA and W? (OK... most of what I know about electricity is DC).

Long and short: I don't think it's heavily loaded. By my calculations it should be good for 5 hours before SOC gets to 50%. So I think those batteries are not heavily loaded and that's going to turn out to be a good thing.



* I think the answer  is that it will draw 0.1A at 100V, and proportionately less current as the voltage increases. IE It's probably about 10W.

Normally the draw is indicated as the worst scenario on the rating of each unit. So the total in use will be far less. It is a low power indeed. 

1 hour ago, Bobster. said:

0.1A at 100 to 240V. What? That can't be 50 watts, can it?

should be 24W absolute worst case scenario, but I doubt it, probably won't be more than 10W, I'd think... hey wadda ya know, I scribbled this before reading your complete posting and I just see you're also giving the 10W theory a 👍 we could both be wrong, though, I don't think by a heck of a lot...

the 160VA is supposed to be taking power factor into account on this page the following appears...

and thus you real wattage may be significantly less than the 160VA, ideal would be using a clamp on ampere meter on one of the battery leads, actually, I think you have two batteries, then you'd have to clamp both positive cables or both negative cables, going to the two batteries to determine the current draw and that times the Voltage, probably 13V is a safe-ish number to use for this back of the napkin calculation, but you can also measure it, should give you the W provided by the battery for the load in question...