shovelhead Posted September 3 Share Posted September 3 As I understand it, not all batteries have chassis ground points. I have not grounded my chassis and recently decided to check for stray voltages. I measure 42V AC between my inverter and battery chassis. Has anyone else checked this and care to share their experience? Quote Link to comment Share on other sites More sharing options...
zsde Posted September 3 Share Posted September 3 Just for clarity, where on the Inverter do you place your voltmeter probe? Is this between Inverter chassis and battery chassis? Quote Link to comment Share on other sites More sharing options...
shovelhead Posted September 3 Author Share Posted September 3 31 minutes ago, zsde said: Just for clarity, where on the Inverter do you place your voltmeter probe? Is this between Inverter chassis and battery chassis? @zsde Correct, between the grounding point on the inverter chassis and the grounding point on the battery chassis. Quote Link to comment Share on other sites More sharing options...
zsde Posted September 4 Share Posted September 4 Is this a grid tied installation? If so, have you tested this if isolated from the grid? Quote Link to comment Share on other sites More sharing options...
zsde Posted September 4 Share Posted September 4 @Scorp007 @TaliaB your thoughts? Quote Link to comment Share on other sites More sharing options...
Beat Posted September 4 Share Posted September 4 Interesting point! I had an incident in the very beginning: When I connected the inverters (Axpert MKS5K) USB comm at the same time as the BMS RS232 to the same laptop it burned the inverters communication board. Since then I use separate laptops. As I read this topic I bothered to measure between the two communication grounds: 53V AC! So I decided to wire batteries ground to inverters ground terminal as next project. Other observation: For BMS monitoring I have a RS485 bus running over all packs. Lately I noted that due to rude manipulation on the cable between two packs the ground wire of the RS485 broke. Surprisingly the communication continues. I assume that the BMS comm ground is probably connected to the neg terminal as these are the only electrical connections between the packs. Quote Link to comment Share on other sites More sharing options...
shovelhead Posted September 4 Author Share Posted September 4 (edited) 4 hours ago, zsde said: Is this a grid tied installation? If so, have you tested this if isolated from the grid? @zsde Yes, it is grid tied, but no difference when isolated from the grid. There is an earth-neutral bond so essentially I wouldn't have expected a difference. Edited September 4 by shovelhead Quote Link to comment Share on other sites More sharing options...
shovelhead Posted September 4 Author Share Posted September 4 1 hour ago, Beat said: Interesting point! I had an incident in the very beginning: When I connected the inverters (Axpert MKS5K) USB comm at the same time as the BMS RS232 to the same laptop it burned the inverters communication board. Since then I use separate laptops. As I read this topic I bothered to measure between the two communication grounds: 53V AC! So I decided to wire batteries ground to inverters ground terminal as next project. Other observation: For BMS monitoring I have a RS485 bus running over all packs. Lately I noted that due to rude manipulation on the cable between two packs the ground wire of the RS485 broke. Surprisingly the communication continues. I assume that the BMS comm ground is probably connected to the neg terminal as these are the only electrical connections between the packs. @Beat have you grounded batteries to inverter already in other words? If so, did you daisy chain the earth from the inverter to battery, to next battery...or star topology all to DB earth point? Just wondering if the latter is best practice? Quote Link to comment Share on other sites More sharing options...
TaliaB Posted September 4 Share Posted September 4 (edited) 23 hours ago, shovelhead said: As I understand it, not all batteries have chassis ground points. I have not grounded my chassis and recently decided to check for stray voltages. I measure 42V AC between my inverter and battery chassis. Has anyone else checked this and care to share their experience? Some checks is your inverter chassis grounded to the utility main earth point. If yes then use the earth on your inverter chassis to ground all your battery chassis only. The most common method of system earthing on the DC side of the installation is floating, i.e.,neither the positive nor the negative terminal of the DC source is earthed. However, a Protective Earth connection shall be implemented for exposed metallic parts in all installations. Edited September 4 by TaliaB zsde 1 Quote Link to comment Share on other sites More sharing options...
shovelhead Posted September 4 Author Share Posted September 4 53 minutes ago, TaliaB said: Some checks is your inverter chassis grounded to the utility main earth point. If yes then use the earth on your inverter chassis to ground all your battery chassis only. The most common method of system earthing on the DC side of the installation is floating, i.e.,neither the positive nor the negative terminal of the DC source is earthed. However, a Protective Earth connection shall be implemented for exposed metallic parts in all installations. @TaliaB Yes, the inverter chassis is directly earthed to the main earth point in the DB. Question/s though: - Is it OK to daisy-chain the earth point from the inverter to the 1st battery, and then from that battery to the next, etc.? Or does each battery need an earth cable to the DB? - In order to tie the inverter and batteries together, would it be advisable to power everything down in order to let the induced voltages dissipate first? - Lastly, any theories on how this voltage is induced in the first place? Quote Link to comment Share on other sites More sharing options...
Beat Posted September 4 Share Posted September 4 2 hours ago, shovelhead said: have you grounded batteries to inverter already in other words? If so, did you daisy chain the earth from the inverter to battery, to next battery...or star topology all to DB earth point? Just wondering if the latter is best practice? No, I haven't yet. It's my next project. I plan to make an aluminum bar on the chassis rack mount lips out of old burglar bars. Then from there just one wire to the inverter. shovelhead 1 Quote Link to comment Share on other sites More sharing options...
TaliaB Posted September 4 Share Posted September 4 (edited) 2 hours ago, shovelhead said: Is it OK to daisy-chain the earth point from the inverter to the 1st battery, and then from that battery to the next, etc.? Yes that would be fine. Before you tie the inverter earth to the battery use your DMM on amp scale and measure if their is any current flow between battery and inverter chassis. 2 hours ago, shovelhead said: In order to tie the inverter and batteries together, would it be advisable to power everything down in order to let the induced voltages dissipate first? If you get negligence current flow between battery chassis and inverter chassis earth then you can just do the earth connections with inverter running just be careful not to accidentally short out battery terminals. You could use between batteries what is called in the electrical industry as "bamba strap" copper strip with perforated holes then from there 6mm² Green/ Yellow earth wire. 2 hours ago, shovelhead said: Lastly, any theories on how this voltage is induced in the first place? It could just be potential difference due to lack of grounding the current test with the DMM should clarify if it might just be static build up.Below picture of the earth strap. Edited September 4 by TaliaB shovelhead 1 Quote Link to comment Share on other sites More sharing options...
Scorp007 Posted September 4 Share Posted September 4 2 hours ago, shovelhead said: @TaliaB Yes, the inverter chassis is directly earthed to the main earth point in the DB. Question/s though: - Is it OK to daisy-chain the earth point from the inverter to the 1st battery, and then from that battery to the next, etc.? Or does each battery need an earth cable to the DB? - In order to tie the inverter and batteries together, would it be advisable to power everything down in order to let the induced voltages dissipate first? - Lastly, any theories on how this voltage is induced in the first place? Earth as was suggested. The only way not allowed is if the battery had 2 earthing point will be to use the casing as a means of connecting 1 earth wire to the next. The wires have to be connected on the same stud/screw. Electronic equipment can have leakage stray values. When measuring the amps one will quickly see if it is stray values. We recently found stray readings on a scope and I solved it by adding a earth wire from scope to a 3 pin plug connected into a multi plug. shovelhead 1 Quote Link to comment Share on other sites More sharing options...
TaliaB Posted September 4 Share Posted September 4 20 minutes ago, Scorp007 said: Electronic equipment can have leakage stray values. When measuring the amps one will quickly see if it is stray values. Yes that is true most pwm supplies uses mov's that has tiny current leakage to earth it is called intentional leakage current and if you have enough electronics and surge protection plug protectors you will have your RCD tripping without any real fault current leakage from appliances. Scorp007 1 Quote Link to comment Share on other sites More sharing options...
Beat Posted September 5 Share Posted September 5 I took the idea of @TaliaB and installed a copper strap across the packs as I have some of such ling around. From the end a 2.5mm² wire to the earth terminal of the inverter. However it did not change anything to the comm ground of the BMS. Some 53V AC remain between it and the inverter comm ground. I wonder if the people who operate BMS to inverter comm (CAN) do not encounter such problems. Do they use optocouplers? Quote Link to comment Share on other sites More sharing options...
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