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Need help troubleshooting a pure sine wave battery backup inverter system

DrSee

Dec 11, 2022
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Hi and thank you in advance for your assistance. As my bio says, I am a retired field service engineer in the field of biomedical electronics. My area of expertise was radiology systems including digital x-ray systems and MRI machines. I left the field after suffering an on-the-job injury in 2005 and my skills have become very rusty.

I recently retired to the Caribbean where I purchased two condo units: one to live in and one to rent out. Both units came with pure sine wave battery backup inverter systems - necessary because of the dirty power here and the frequent power outages.

When Fiona blew through here a few weeks ago, my inverter system supplied power for 19 hours before running out of juice. When the power came back on, I noticed the system no longer charges properly and the fan stays on all the time. The guy we usually have work on the inverter systems here is no longer available. The onsite maintenance guy has limited experience with these systems and I have none.

My system now only charges to between 60 and 70% and the fan never shuts off. When it does charge to 100%, tt takes days to do so and the fan runs constantly. I have taken to putting the system back on city power and turning the inverter off until needed. When I do turn the inverter back on, the display shows only 60 to 70% charge (depends on how many hours the system has been turned off).

To me, based on my years of experience with portable x-ray machines, this indicates one or more of the batteries has/have failed but the local guy insists this is not the case. He says it could be something as simple as the system needing to be recalibrated. I doubt this as the inverter in the rental unit is operating fine according to my tenant.

I have no clue who manufactured this unit and do not have any owner’s or service manuals or schematics available so I am at a loss for troubleshooting the system. There is no indication what the make and model is and to be honest, the way they do repairs here, I’m not even sure the repair tech used the correct parts for those times he had to perform repairs.

I’m hoping someone here with pure sine wave inverter experience can provide assistance. I have only a multimeter available for troubleshooting and no clue where to obtain an o’scope, if needed.

Can someone on here help?

Again, thank you.

Mike
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kellys_eye

Jun 25, 2010
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Those batteries look suspiciously like lead acid (sealed lead acid perhaps?)

If they are then they've been over-discharged and are probably dud. The issues surrounding difficult/lengthy recharge also point to the fact.
 

DrSee

Dec 11, 2022
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Dec 11, 2022
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Thank you for responding Kellys_Eye. Yeah, that’s what I’m thinking too. And the local guy just refilled the distilled water right before Fiona hit. Getting him to confirm a failed battery has been difficult. The lack of training for “skilled” positions here on the island is unbelievable. The batteries are the ones supplied by the service tech outta Santo Domingo and are less than a year old. He’s no longer servicing this area - the 3 hour each way drive finally got to him. Any warranty left on the batteries is a moot point as he won’t replace them. What batteries should I be using? I’ve not kept current on the technology.

My neighbors and I have been talking about switching to solar but the condo administration is being resistant to the idea. We also don’t have much space on our rooftops for the panels, so solar may not be viable.

Thanks again.
 

kellys_eye

Jun 25, 2010
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Measure the individual battery voltages and compare with the manufacturers spec for 'fully charged'. If they'd don't get there then they are definitely dud and no amount of 're-calibration' or distilled water is going to fix them.

What batteries you change to depends on what type your inverter/charger will support. 'Anything' is better than lead-acid (which is particularly poor for 'depth' of discharge) but not all chargers will support lithium or LiFePO (the best of the bunch).

T'aint gonna be cheap either - if you know how long you want battery back-up to last it would help figure out how many cells you need too.

Given where you are, a solar arrangement would be ideal and you don't need a lot of panels to make it work. If the local power supply is reasonably regular i.e. not off every day etc then a small solar arrangement (200W even) would charge your battery bank over a period of 24 hours (total) sunlight (guessing by its size - you'd have to let us know the capacity of the batteries).
 

DrSee

Dec 11, 2022
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Again, thank you. I do know how to check the batteries but getting the local tech to cooperate in doing so is the problem. He’s insistent it can’t be the batteries so won’t provide the tools and test equipment. All of my stuff is in storage in the states and I haven’t gotten to the store to replace them here. Truthfully, until our inverter guy stopped coming out here, I had no need. I’ll be in town tomorrow so will stop by the ferretería (hardware store) on my way home. I’m disabled so am reliant on our local tech guy for the heavy lifting. Maybe I can get him to lift the batteries down if I’m doing the measuring and using my own equipment.

I’ll reach out to the condo administration and see if they’ll allow solar. There’s a solar installer about 30 km from here. Unfortunately he refuses to work on inverters for battery backup systems for some reason. Perhaps he doesn’t feel qualified. I spoke with one of his customers a year or so ago and he swears by the solar systems. His electric bill dropped from around [imath]200 per month to[/imath]5, so they’re definitely worth it. And he gets paid for any excess electricity he feeds back to the power company. (I think that’s how his bill ended up around [imath]5 per month, so it’s actually higher but then the power company pays him for the excess for a net total of[/imath]5 per month.)

Because we have no clue who the inverter’s manufacturer is, and no documentation for it, we have no way of knowing what batteries it’ll support. The existing batteries are from Trojan Battery Company in the states so I’m going to reach out to them to see if I can get replacements shipped here. I’m not looking forward to the customs taxes…..
 

kellys_eye

Jun 25, 2010
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Not sure about the country you're in but here in the UK (and, I suspect, many other countries too) you have to have a professional and certified solar installation to feed back into the local/national grid (a grid-tied setup). This imposes additional costs that may not be recovered in any short period unless your system is sized to back-feed a considerable amount of surplus energy - given the potential limitations imposed by your landlord(?) you might only get away with a non-fixed installation of limited size. You will still save money but not 'make' money.

Your charger/inverter looks to be of a generic design similar to this:


and the good news is that it seems to support lithium batteries (and LiFePO). Do you have a comprehensive operators manual? This would show the procedure for changing the battery type - something I'd recommend rather than continuing with lead-acid which will (again) fail if over-discharged and only have a limited charge/recharge life anyway (lithium/LiFePO have a much longer cycle life). The cost of Lithium will obviously be higher but they will survive 'deep' discharge and last longer plus give a longer AC power delivery time for the same physical volume.

Lastly (for now!) the addition of a solar panel system will require an additional device (solar charge controller) which would normally be sized to match the solar panels you use so if you go that route ensure you get all the parts from a single source and get the to spec the system as a whole.
 

DrSee

Dec 11, 2022
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Thanks for your follow-up. No, I don’t have either an operator’s or service manual for this unit. None of my neighbors do either from what I can tell. We each own our condos and because there is not yet an HOA, we have to get permission from the condo developer to do any structural changes to the common areas. The good news is that there is a certified solar installer in the area. I’m just waiting to learn from the developer if he’ll allow solar panel installation on the roof. And I also know that I’ll need a solar charge controller. The local installer will have it if we’re allowed to do a solar install.

I would love to switch to lithium or LiFePo batteries. If I can find another inverter professional who knows this unit, I will definitely ask about it. I have four six volt batteries hooked up in series so if I’m remembering my battery theory correctly, that gives me 24VDC into the inverter.

I did find a manual online but do not know if it will work with this unit. I agree that it’s probably a generic system but am hesitant to begin monkeying around with it without a professional to back me up should I make a mistake.

I’m just waiting now for my tenant to move out later this month and I’ll “steal” the batteries from that unit. The last time I suggested that though, the local maintenance guy said he wouldn’t move them because the system would need to be recalibrated for those batteries and he doesn’t know how to do that. That doesn’t make sense to me because if the system is working correctly, it should accept them without recalibration. Maybe he meant the system would have to be re-balanced for the different batteries? It’s been almost 20 years since I last worked on a mobile x-ray unit and I don’t remember ever having to re-calibrate for new batteries. Perhaps I’m misremembering….
 

kellys_eye

Jun 25, 2010
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You could 'play' with the programming controls so long as you don't 'accept' any parameters i.e. just scroll through the various options to see what's on offer. You'll probably come across 'battery type' as one option and see that you can chose lead-acid, lithium etc. No harm done if you're attentive (and given your history.....)

The concept of 'recalibration' is just an excuse made up by someone who doesn't know what they're doing and can't interpret simple on-screen instructions. Once battery 'type' is selected (and perhaps the terminal voltage i.e. 12V, 24V, 48V whatever) the unit will have basic settings to work 'straight out of the box'. The voltage is usually 'fixed' though so your system is supplied/designed to work with 24V battery banks.

The link I gave to the generic device might lead to an operators manual - or other similar devices may do so (have a Google search) - and the menu structure, given the identical LCD readouts, will probably be the same across the range so somewhere to start, at least.

This link seems to match your setup (and the various power levels are matching too) so download it and 'have a play':

 
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