Stecher Adolf Posted February 15 Share Posted February 15 I recently bought a new Fivestar 24V 3.5KVA 3.5KW 80A MPPT hybrid inverter for my UPS / solar system. The installation comprises the above inverter and two Mecer 12V200Ah Lithium Iron Phosphate Battery SOL-B-L-M200, Model: EC4S2P200. Both 12V batteries are wired in series and connected to the above inverter. Both batteries are fully charged and the open circuit voltage is 27.4Vdc. The 24V battery circuit is protected by a 100Adc circuit breaker. The rated NiFe battery charge / discharge current is 100Adc. Problem As soon as I close the 100Adc circuit breaker, the battery voltage at the inverter terminals drops to 0Vdc without an overload or short-circuit trip of the CB. The resistance between the inverter + / - terminals = 0.4 Ohm, which should result in a startup current not exceeding 67.5 Adc. However, I do not know the inverter dynamics during startup. The inverter display shows a flashing “bP” battery symbol. Assumption I assume that the actual inverter cold-start current (don't know the value) causes the battery management system (BMS) to shut down in order to protect the batteries. I only have a very basic understanding of a BMS's functionality. Request Kindly assist with advice as to how to resolve this problem. Quote Link to comment Share on other sites More sharing options...
stefan44 Posted February 15 Share Posted February 15 Good day, what is the individual voltage of the 12v batteries? it might be that one battery is at 14.6V (fully charged) and the other at 12.8V ( almost empty rest voltage) and as soon as the inverter try to energize the caps the current demand is too big, the low voltage battery shuts down resulting in a open circuit in your battery wiring. if this is the case you can charge the low SOC battery with a 12v charger until the voltage match or almost match the other battery's voltage, then connect them in parallel and charge again with a 12v charger. this is called balancing it will be a good idea to invest in a battery balancer. Quote Link to comment Share on other sites More sharing options...
Kalahari Meerkat Posted February 15 Share Posted February 15 1 hour ago, Stecher Adolf said: Kindly assist with advice as to how to resolve this problem. Maybe with a 10 Ohm 10W resistor. try and pre-charge the capacitors in the inverter before switching on the battery, depending on the inverter, the inrush current required to do this could be significant and this could trigger one of the 12V batteries' BMS to wave the white flag... @stefan44 's thinking could also be correct, its never ideal to have two separate batteries in series, without some balancing between them, one of the batteries could be "propvol" whilst the 2nd one is totally empty... so check this and @stefan44 maybe quote some of the text you are responding to, or at lest quote the relevant users name, then they will get a notification that someone has responded, which they will not otherwise, unless they specifically "watch" the thread started or posted into... Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted February 15 Author Share Posted February 15 1 hour ago, stefan44 said: Good day, what is the individual voltage of the 12v batteries? it might be that one battery is at 14.6V (fully charged) and the other at 12.8V ( almost empty rest voltage) and as soon as the inverter try to energize the caps the current demand is too big, the low voltage battery shuts down resulting in a open circuit in your battery wiring. if this is the case you can charge the low SOC battery with a 12v charger until the voltage match or almost match the other battery's voltage, then connect them in parallel and charge again with a 12v charger. this is called balancing it will be a good idea to invest in a battery balancer. Hi Stefan, Thanks for your response. The open circuit voltage for battery A =13.76V and B=13.62V. I did charge the batteries independently to have both voltages as close as possible. As, according to the battery manufacturer, my 12V LiFe batteries are not suitable for parallel operation I cannot apply your balancing proposal. However, when bouncing my problem off with Mecer, they suggested a battery balancer too. I much appreciate you reply. Adol Quote Link to comment Share on other sites More sharing options...
JustinSchoeman Posted February 15 Share Posted February 15 A balancer is always a good idea. But the symptoms seem to be related to a start-up current surge. Bypass the breaker with a 24v lamp (or even 250v incandescent lamp if this is all you have). Let this charge the inverter input a bit before closing the breaker. Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted February 15 Author Share Posted February 15 30 minutes ago, Kalahari Meerkat said: Maybe with a 10 Ohm 10W resistor. try and pre-charge the capacitors in the inverter before switching on the battery, depending on the inverter, the inrush current required to do this could be significant and this could trigger one of the 12V batteries' BMS to wave the white flag... @stefan44 's thinking could also be correct, its never ideal to have two separate batteries in series, without some balancing between them, one of the batteries could be "propvol" whilst the 2nd one is totally empty... so check this and @stefan44 maybe quote some of the text you are responding to, or at lest quote the relevant users name, then they will get a notification that someone has responded, which they will not otherwise, unless they specifically "watch" the thread started or posted into... Hi Kalahari Meerkat, I did actually a battery load-test, over about two hours, using a 20 Ohm resistor in series with the batteries and the inverter to establish some idea about the load performance. Would this have pre-charged the inverter capacitors, as suggested by you? From your comment I deduce that you also think the problem lies with the batteries and using a balancer might be the solution. I much appreciate your comment. Thank you. Adolf Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted February 15 Author Share Posted February 15 8 minutes ago, JustinSchoeman said: A balancer is always a good idea. But the symptoms seem to be related to a start-up current surge. Bypass the breaker with a 24v lamp (or even 250v incandescent lamp if this is all you have). Let this charge the inverter input a bit before closing the breaker. Hi justin, Thank you for your proposal which I will try it as soon as I have the inverter back from testing. In the meantime I decided to install a balancer and hope this will be the end of my troubles. Also your input is much appreciated and I will let you know about the final outcome. Many thanks. Adolf Quote Link to comment Share on other sites More sharing options...
Kalahari Meerkat Posted February 15 Share Posted February 15 51 minutes ago, Stecher Adolf said: As, according to the battery manufacturer, my 12V LiFe batteries are not suitable for parallel operation I cannot apply your balancing proposal. Ok, but if you have a 12 Volt charger, then it is quite legit to parallel up the 2 batteries and charge them this way, and maybe after reaching a set charging Voltage, let's say 14V, see if there is still current flowing between the 2 batteries, after the charger has been disconnected, if nothing significant, less than 0.1 Amp, then the batteries should have at least close to the same voltage, even if not 100% balanced. They should not be discharged in parallel, connected to a 12V inverter, for instance, since one battery could go into protection for whatever reason and the 2nd one would have to supply twice the current, because of this.... 36 minutes ago, Stecher Adolf said: I did actually a battery load-test, over about two hours, using a 20 Ohm resistor in series with the batteries and the inverter to establish some idea about the load performance. Would this have pre-charged the inverter capacitors, as suggested by you? Yes and no, if the inverter was purely running off the batteries, then this charge voltage would have been consumed as soon as you disconnected the batteries. To precharge you should have the inverter switched off, then precharge the battery terminals and then connect/switch on the battery, now you should be able to switch on the inverter and the current drawn now should not be huge, unless you have a huge load on the inverters output... Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted February 15 Share Posted February 15 6 hours ago, Stecher Adolf said: Hi Stefan, Thanks for your response. The open circuit voltage for battery A =13.76V and B=13.62V. I did charge the batteries independently to have both voltages as close as possible. As, according to the battery manufacturer, my 12V LiFe batteries are not suitable for parallel operation I cannot apply your balancing proposal. However, when bouncing my problem off with Mecer, they suggested a battery balancer too. I much appreciate you reply. Adol From the voltage you measured these batteries are at a high SOC. As far as parellel is concerned I have had my 2 similar batteries in parallel for many months and they are currently as well and no problem. I have not come across much that warns about connecting lithium in parallel. I do balance the 2 in parallel even when charging and no change in voltage as in your case. My batteries are over 3yrs old and still going strong. Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted February 16 Author Share Posted February 16 17 hours ago, Scorp007 said: From the voltage you measured these batteries are at a high SOC. As far as parellel is concerned I have had my 2 similar batteries in parallel for many months and they are currently as well and no problem. I have not come across much that warns about connecting lithium in parallel. I do balance the 2 in parallel even when charging and no change in voltage as in your case. My batteries are over 3yrs old and still going strong. Hi Scorp007, thanks for your suggestion and explanation wrt parallel charging / balancing, it makes sense to me for initial charging with my 12Vdc charger. However, as my inverter is a 24Vdc model, I obviously need the batteries in series for operation. The Mecer technical LiFe battery spec. says "SOL-B-L-M200. No Parallel charging ability and max 4 in Series". Any way, its educational and encouraging to receive these kind of comments and helps me to see some light at the end of the tunnel. Will feedback with an explanation once my inverter is doing what it is supposed to do. Regards Adolf Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted February 16 Author Share Posted February 16 23 hours ago, Kalahari Meerkat said: Ok, but if you have a 12 Volt charger, then it is quite legit to parallel up the 2 batteries and charge them this way, and maybe after reaching a set charging Voltage, let's say 14V, see if there is still current flowing between the 2 batteries, after the charger has been disconnected, if nothing significant, less than 0.1 Amp, then the batteries should have at least close to the same voltage, even if not 100% balanced. They should not be discharged in parallel, connected to a 12V inverter, for instance, since one battery could go into protection for whatever reason and the 2nd one would have to supply twice the current, because of this.... Yes and no, if the inverter was purely running off the batteries, then this charge voltage would have been consumed as soon as you disconnected the batteries. To precharge you should have the inverter switched off, then precharge the battery terminals and then connect/switch on the battery, now you should be able to switch on the inverter and the current drawn now should not be huge, unless you have a huge load on the inverters output... Thank you Kalahari Meerkat for this additional suggestion, I understand your reasoning and will follow your procedure once I have the inverter back. Will keep you posted with the outcome. Keep well! Adolf Quote Link to comment Share on other sites More sharing options...
Stecher Adolf Posted March 5 Author Share Posted March 5 On 2024/02/16 at 1:00 PM, Stecher Adolf said: Thank you Kalahari Meerkat for this additional suggestion, I understand your reasoning and will follow your procedure once I have the inverter back. Will keep you posted with the outcome. Keep well! Adolf Adolf Stecher; Inverter / Battery Problem Follow-up Thank you, Kalahari Meerkat, Scorp007, Justin and Stefan; for your response to my problem which eventually helped me to get my Fivestar inverter up and running. It was the suggested bypassing of the open battery circuit-breaker with an ~ 20 Ohm resistor for about 5-7 minutes that caused the initially flashing battery-charging symbol to go to steady and start the inverter charging the batteries. This happened last Friday after I received the inverter back from the supplier. Since then, I didn’t experience any further problems. It is good to know that there are knowledgeable professional on this forum who take the time and effort to listen to problems and to respond in a meaningful and practical way to resolve the issues at hand. Something I definitely cannot say about the inverter supplier. Thanks again to all of you. Adolf Stecher Quote Link to comment Share on other sites More sharing options...
Kalahari Meerkat Posted March 5 Share Posted March 5 3 hours ago, Stecher Adolf said: It was the suggested bypassing of the open battery circuit-breaker with an ~ 20 Ohm resistor for about 5-7 minutes that caused the initially flashing battery-charging symbol to go to steady and start the inverter charging the batteries. V/R=I aka V/I=R aka R*I=V V would be 25V or thereabouts, R you said app. 20 Ohm, thus 25/20=1.25Amperes, which for 10 seconds or so, should have been plenty, but a 1 or 2 Ohm resistor, for a second or two, would also have been fine, since 25V/1Ohm=25Ampere, which your battery should have been happy to supply without anything else tripping, I would think... Anyway, glad it is all working now... Quote Link to comment Share on other sites More sharing options...
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