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Open Roads Forum  >  Tech Issues

 > Renogy 100ah LifePo4 Lithium - Max Surge Current

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BFL13

Victoria, BC

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Posted: 12/02/19 05:18pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

I don't think a microwave has much surge at the start. s/b easy to stay under 100 amps. Only real surge in an RV would be an air conditioner and that is not really a concern if you are limited to one battery.


A "700w" Danby MW we had wanted 1050w input and made the 1000w PSW inverter pull 100 amps as seen on the Trimetric. The inverter showed its overload light but kept running. After a few times doing that, the inverter burnt out some components on its circuit board.


1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.

MDKMDK

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Posted: 12/02/19 05:43pm Link  |  Quote  |  Print  |  Notify Moderator

From the Owners Manual, an Onan QD3200 diesel generator can draw up to 675 CCA under very cold conditions, with a draw of 475A just to get it to turn over at ambients down to 0F. I believe I read somewhere that they can suck up to 300A to start at more comfortable/normal temps.
Once again, any electric (starter) motor or other mechanical device can draw mucho amps when starting/running.


Mike.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)

BFL13

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Posted: 12/02/19 05:52pm Link  |  Quote  |  Print  |  Notify Moderator

There are "inductive" loads and "resistive" loads, but also you get "in-rush" like with converters, and "surges" like with motors winding up. I got lost trying to figure out if any of them is the same thing as another.

"They" do advise if your inverter won't run an inductive load at full speed, just add a resistive load like an incandescent lamp to the mix.
That might only apply to MSW inverters, don't know.

I don't know if that trick would help with an Li's BMS.

3 tons

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Posted: 12/04/19 11:55am Link  |  Quote  |  Print  |  Notify Moderator

As I seem to recall reading somewhere, LiFePo4 is not intended to be used as an enginestarting battery, thus is not rated in CCA, but I can’t be certain...Just saying.

time2roll

Southern California

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Posted: 12/04/19 12:03pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

time2roll wrote:

I don't think a microwave has much surge at the start. s/b easy to stay under 100 amps. Only real surge in an RV would be an air conditioner and that is not really a concern if you are limited to one battery.


A "700w" Danby MW we had wanted 1050w input and made the 1000w PSW inverter pull 100 amps as seen on the Trimetric. The inverter showed its overload light but kept running. After a few times doing that, the inverter burnt out some components on its circuit board.
You need a Panasonic 'inverter' microwave.
Set to low power these actually draw less current instead of cycling the megatron.


2001 F150 SuperCrew
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BFL13

Victoria, BC

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Posted: 12/04/19 12:16pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

BFL13 wrote:

time2roll wrote:

I don't think a microwave has much surge at the start. s/b easy to stay under 100 amps. Only real surge in an RV would be an air conditioner and that is not really a concern if you are limited to one battery.


A "700w" Danby MW we had wanted 1050w input and made the 1000w PSW inverter pull 100 amps as seen on the Trimetric. The inverter showed its overload light but kept running. After a few times doing that, the inverter burnt out some components on its circuit board.
You need a Panasonic 'inverter' microwave.
Set to low power these actually draw less current instead of cycling the megatron.


Yes, that would be an advantage for using a bigger MW that can hold bigger pots without pulling more amps via inverter. That 700w was too small.

As it is the MH we have now has a big enough 1991 Dometic "RV" MW which will only run on PSW, and we are ok with the 2000w PSW inverter we have now. Newer MWs will run on MSW (BTDT), but not this 1991 job.

Itinerant1

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Posted: 12/04/19 01:07pm Link  |  Quote  |  Print  |  Notify Moderator

For what it's worth...

https://www.ev-power.eu/blog/LiFePO4/LFP-as-starting-battery.html

From that link...

LFP as a starting battery – two concerns

Question: I want to use the LFP battery (4x 3.2V cells) for starting of my car. What SBM (simple battery management board) should I use to protect the battery?

You cannot use a SBM to protect the starting battery. For starting the car, the current will be very high, hundreds or even nearly 1000 Amps, it is not possible to disconnect such high currents.

WARNING: Additionally it is not possible to disconnect the battery from vehicle circuits. The car electronics may burn or become faulty of the battery is suddenly removed from the circuit, as a result of disconnection, during the operation (when the engine is running).

To install LFP battery, the battery must be hard wired to the car, the same way as the lead acid battery is. This brings some risks and problems:

1) No disconnection, no fuse. Note that the car battery is wired without any fuse or disconnection ! ! ! This is a huge risk that exists in all cars. It is crazy, but this is the reality. Yes, this is the most crazy thing about all cars you see in the streets — no high power fusing or disconnection of the 12V battery. This is also one of the main reasons for the many car fires – the fire starts from short circuit on the battery that cannot be disconnected from the car…… so the car will burn completely.

There is less of a issue with the Lead Acid battery, as the Lead Acid battery can give the power for a short time, and it will stat loosing the peak power rating, after longer time of high current discharge.

However for LFP battery, in case of short circuit, the battery will release all power suddenly, constantly and continuously. The LFP battery has much more power that the lead acid battery.

ADVICE: Our definite suggestion is to install a high-power rating fuse for the LFP battery. The rating of the fuse should be 300Amp or even more depending on the starting currents for your application.


2) Deep discharge. If you left your car for long time without care, the on-board electronics (e.g. alarm, security systems, car radio, etc….) will drain the battery to completely empty – the deep discharge. In some cars the battery will be depleted as quickly as in two weeks.

This is a lesser issue for the Lead Acid battery, as most Lead Acid batteries can survive the deep discharge. They can be recharged and they will perform in a reasonable way again. However this is not possible with the LFP battery. If you deep discharge the LFP battery, it is damaged for ever and there is no way to restore it to function.

ADVICE: Our suggestion is that the LFP battery should be fully disconnected from the car in case you park the car and the car will not be used for a longer period of time.

* This post was edited 12/04/19 01:42pm by Itinerant1 *

time2roll

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Posted: 12/04/19 01:21pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

...... and we are ok with the 2000w PSW inverter we have now. Newer MWs will run on MSW (BTDT), but not this 1991 job.
I would not buy any inverter over 1000w to be connected to lithium battery of 100 amp max current. Probably 800w max inverter for best results.

I realize you have more battery but we are talking about a current limited lithium battery.

BFL13

Victoria, BC

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Posted: 12/04/19 02:02pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

BFL13 wrote:

...... and we are ok with the 2000w PSW inverter we have now. Newer MWs will run on MSW (BTDT), but not this 1991 job.
I would not buy any inverter over 1000w to be connected to lithium battery of 100 amp max current. Probably 800w max inverter for best results.

I realize you have more battery but we are talking about a current limited lithium battery.


My point was that AFAIK there is not any MW small enough for that, where a 700w is already 1050w for input.

So Li does not change the basics same as Wet or AGM that you need more than 100AH if you want to run a MW unless there is a smaller size Panasonic inverter type you can run at half power maybe.

MDKMDK

Canada

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Joined: 10/15/2008

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Posted: 12/04/19 03:26pm Link  |  Quote  |  Print  |  Notify Moderator

Itinerant1 wrote:

For what it's worth...

https://www.ev-power.eu/blog/LiFePO4/LFP-as-starting-battery.html

From that link...

LFP as a starting battery – two concerns

Question: I want to use the LFP battery (4x 3.2V cells) for starting of my car. What SBM (simple battery management board) should I use to protect the battery?

You cannot use a SBM to protect the starting battery. For starting the car, the current will be very high, hundreds or even nearly 1000 Amps, it is not possible to disconnect such high currents.

WARNING: Additionally it is not possible to disconnect the battery from vehicle circuits. The car electronics may burn or become faulty of the battery is suddenly removed from the circuit, as a result of disconnection, during the operation (when the engine is running).

To install LFP battery, the battery must be hard wired to the car, the same way as the lead acid battery is. This brings some risks and problems:

1) No disconnection, no fuse. Note that the car battery is wired without any fuse or disconnection ! ! ! This is a huge risk that exists in all cars. It is crazy, but this is the reality. Yes, this is the most crazy thing about all cars you see in the streets — no high power fusing or disconnection of the 12V battery. This is also one of the main reasons for the many car fires – the fire starts from short circuit on the battery that cannot be disconnected from the car…… so the car will burn completely.

There is less of a issue with the Lead Acid battery, as the Lead Acid battery can give the power for a short time, and it will stat loosing the peak power rating, after longer time of high current discharge.

However for LFP battery, in case of short circuit, the battery will release all power suddenly, constantly and continuously. The LFP battery has much more power that the lead acid battery.

ADVICE: Our definite suggestion is to install a high-power rating fuse for the LFP battery. The rating of the fuse should be 300Amp or even more depending on the starting currents for your application.


2) Deep discharge. If you left your car for long time without care, the on-board electronics (e.g. alarm, security systems, car radio, etc….) will drain the battery to completely empty – the deep discharge. In some cars the battery will be depleted as quickly as in two weeks.

This is a lesser issue for the Lead Acid battery, as most Lead Acid batteries can survive the deep discharge. They can be recharged and they will perform in a reasonable way again. However this is not possible with the LFP battery. If you deep discharge the LFP battery, it is damaged for ever and there is no way to restore it to function.

ADVICE: Our suggestion is that the LFP battery should be fully disconnected from the car in case you park the car and the car will not be used for a longer period of time.


A lead acid battery can withstand a "deep discharge" better than lithium? I think that's arguable.
Every manufacturer of lithium iron phosphate suggests in their documentation that you can run a LiFePO4 to zero and as long as you remove the loads and recharge it immediately, it will recover just fine and you'll do less damage to it, than to a FLA run to zero. The FLA might not even recharge at all, depending on circumstances. Or you'll have to hit it with a lot more amperage than you might have available in most chargers, just to get it over the "Frankenstein activation hump".
The cold cranking amps issue is the real problem, as starters will draw a lot of amps for a short period to turn the engine over. The BMS in most batteries will prevent that occurrence, and cut discharge. However there are some that have been adjusted to allow a much higher surge discharge, as I pointed out previously, with examples.

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