Maximum Continuous Discharge Current - Lithium - Confused?

[IanRJ]

I know its not difficult to confuse me but its happened again

I'm in the process of resourcing the bits and pieces for my change to Lithium and an inverter fitting. Having decided on a Krieger 2kw inverter and two Ultramax 100ah Lithium's, I realised that these particular batteries have a Max Continuous Discharge Current of only 30amps. I checked some of the other Lithium's on the market and some had CDC of 60 - 125 amps.

Given the Inverter may draw 2000w I'm pretty sure that the battery BMS will not support it. I stand ready to be educated...

My confusion is over:

1. The Inverter power output at 240v and the draw at 12v. So, say, 1500w draw of a hair dryer at 240v is 6.25 amps; at 12v 1500w is 125 amps (?).

2. How long is considered maximum continuous in this regard (e.g. 1, 10, 30 minutes) is it a standard?

3. At 30 amp CDC and 12v I think () the max wattage possible without breaking this battery set-up (inverter or no inverter) would be 360 watts with a single battery or 720 watts with two batteries?

So, no-way this battery setup (2*100ah with Max CDC of 30 amps) could support a 2kw or even a 1kw inverter draw?

Advice is welcomed!

 

[Wissel]

Are these the batteries?



If so, they state tha max continuous discharge as 80a?

 

[Lenny HB]

Yes your figures are correct but you need to add 10 to 15 % for inverter inefficiency. so a 240v 1500 watt load would take around 140 amps at 12v.

Edit:
If the same battery as Wissel post, you are confusing charging with discharging rates, max discharge is 80 amps.

 

[Kannon Fodda]

The Sterling Lithiums have a max continuous discharge rate (and charge rate), and then an intermittent 30 second discharge rate, although they don't say in the literature how long an interval between the intermittent periods. Some of the Sterlings can support 100A continuous and double that for the intermittent. I suspect this is where we start to see some of the big differences in Lithium battery pricing.

Reality is all batteries, even the lead-acid, have charge and discharge rates. The lithium may be a bit more sensitive and possibly protected from abuse by the battery management system, but even with lead-acid, or whatever, exceed the rate for long and your battery won't thank you.

 

[IanRJ]

Are these the batteries?



If so, they state tha max continuous discharge as 80a?

Thanks for pointing that out Wissel!

Yes those are the batteries but on the Battery Masters site they are 30 amp Max:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
"Li100-12, 12v 100Ah Lithium Iron Phosphate, LiFePO4 Battery for Mobility Scooter, Electric Vehicles, Golf Trolley, Golf Buggy, Mobility Scooter, electric Wheelchairs, Lawn mowers, Lights, Toy cars, Sprayers, Photovoltaic, Robots, Communications, Electric tools, Pumps, Measuring instruments, AGV (Automatic guided vehicle), Magnetic lifts. A high end replacement for heavy users of Sealed lead acid batteries. Dimensions: L(mm) W(mm) H(mm) 325 165 211. This battery has a maximum 30A continues discharge current. Comes with its own charger: Li Iron/Li Polymer 14.4v 20Ah"
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

I have emailed them to confirm.

Still, at that CDC (80 amp) the max draw would be under a 1kw I believe - but perhaps with two batteries in parallel (960w*2 =1920w - 12% inverter inefficiencies say 1650w) it would operate a 1500w inverter?

Or put another way 1500w at 12v = 125amp + 12% for inverter = 140 amps out of 160 available from 2 batteries?

^{_{Subscribers  do not see these advertisements}}

 

[IanRJ]

The Sterling Lithiums have a max continuous discharge rate (and charge rate), and then an intermittent 30 second discharge rate, although they don't say in the literature how long an interval between the intermittent periods. Some of the Sterlings can support 100A continuous and double that for the intermittent. I suspect this is where we start to see some of the big differences in Lithium battery pricing.

Reality is all batteries, even the lead-acid, have charge and discharge rates. The lithium may be a bit more sensitive and possibly protected from abuse by the battery management system, but even with lead-acid, or whatever, exceed the rate for long and your battery won't thank you.

Yep I get that - thanks for the feedback though! I hadn't even thought of the CDC prior to considering an inverter.

 

[IanRJ]

For anyone who might have been following this thread.

Ultramax have confirmed that these batteries are all now actually 100 amp CDC, The tech Sheets are being updated and the 30/80 amp CDC batteries are no longer available. All still the same price however, with discounts for 2 or more units.