I have a 100 watt panel from Harbor Freight and one from Dokio, I don’t trust myself to test polarity. Anyone know if I need to use the reverse polarity adapter that I got when I bought an extension solar panel cable with my new Bluetti EB 55 ? Thanks hope all are well.
@Jst No reverse polarity adapter is required. The solar panel is connected to our PV charging cable, the positive terminal is connected to the positive terminal, the negative terminal is connected to the negative terminal, and that’s fine.
I don’t have Mc4 connector on my Dokio or Harbor Freight panels, they both have SAE, but the Dokio came with a reverse polarity adapter and a USB, SAE and XT60 conversion adapter. I was going to attach the SAE to XT60 adapter and use that to charge my EB55 with. So, do I understand that using the SAE to XT60 needs no polarity concerns ? Sorry, this is all new to this old lady. I do so appreciate all your help and time. Thank you. Bless you.
@Jst Can you take a picture to show me how the interfaces and connection cable of your solar panel looks like?
Also, the 100w panel you mentioned does not provide voltage parameters, so we are not sure if it can charge the machine.
@Jst Welcome to the forum!! Yes, more then likely you’ll need to get one of those SAE reverse polarity adapters for those harbor freight panels to work with the bluetti unit. Highly recommend ALWAYS using a multi-meter to check polarity and voltage prior to inputting any array tho. Check out youtube and become familiar with how to use a multimeter as they will come in VERY handy in the future as your addiction to the solar world grows… and trust me it will!! hahaha
Heres a link to one of those reverse adapters…
You could also just snip off the SAE cconnector and attach on some new MC4 adapters (which is exactly what I did for my first panels, which were also from harbor freight) I recommend buying a bulk pack and this little “kit” from bougerv… Having extras laying arround is very nice as well, as sometime those clips can snap. Heres the kit that also includes the mc4 crimping tool and some spare parts…
Ohh and check out Nates video on how to wire up the mc4 connections. Hes got tons of helpful beginner videos that have been crucial to my projects and learning!! Heres the link to the mc4 install demo and actually… his next video was the basics on how to use a multimeter! haha Ill link that for you as well!
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Thank you so much for your kind reply. I will be looking at everything that you have suggested. I think that your information is very valuable and I do so appreciate your time and willingness to pass along your know how. All the best to you and yours. And, again, thank you. Jst
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Sorry, my phone is old and takes blurry pictures. I have the Thunderbolt 100 watt solar panel: THUNDERBOLT 100 Watt Monocrystalline Solar Panel – Item 57325 – Harbor Freight Coupons It is 18v/22v open circuit, 6.2 max. amps and SAE connectors. Also, I want to purchase this adapter cable, SAE to Mc4 with polarity adapter: Amazon.com. Hope this contains all the information you will need. Thank you so much for your assistance. All the best to you. Jst
@Jst Because we can’t see what the interface of your solar panel looks like, we can’t accurately determine if you need a reverse polarity adapter. Based on the parameters, the open circuit voltage is in line with EB55 and can charge our machine.
We suggest you also refer to @m.briney 's answer.
Thank you I will look at m.briney, but here is a view of what I think you may need to see: Renogy 100 Watt Solar panel VS Harbor Freight 100 Watt Solar panel - YouTube So as to not waste your time any further, if you start at 57 second in and go to about 1 min. and 15 seconds you will get a good look at the Harbor Freight Thunderbolts panel’s interface on the back. I want to purchase the aforementioned Amazon.com.SAE to Mc4 adapter to use with the Mc4 cable that came with my EB55 for charging with solar. That adapter comes with a reverse polarity adapter if needed. Do I need it is the question.? Hope you have a wonderful day. All the best to you and yours. Thank you, Jst
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@Jst I would recommend getting the adapter, as it might come in handy later, even if you dont need to use it… And I still would HIGHLY recommend getting a multi-meter and checking the polarity before plugging in anything into the inputs of the power stations. This will allow you to make sure that you’re within the solar input range, and also will tell you if your polarity is askew/backwards and if you need that reverse adapter or not. My original 100w harbor freight thunderbolt panels DID need the reverse adapter, but that was purchased a long time ago when they first came out. They might have updated their wiring to become more “standardized” since then… Getting a multimeter and reading the output is really the only clear-cut way to make sure you’re not going to potentially mess anything up.
Pick up a cheapo voltmeter. Everyone should have one, to check batteries, from cars to flashlights, if nothing else. Set it to DC and put each lead in a connector and if it shows a negative voltage, swap the leads around. The red lead will now be on the positive connector. For just checking polarity, you can be inside and just shine a flashlight on it. That should give you enough voltage to see if it’s positive or negative.
For testing a 100 watt panel then it needs to be in the sun; the voltage should be around 18 volts at 5.55 amps, (18 x 5.55 =100 watts.) This is how to check to see if a panel is working right.
I tried to check the polarity of the panel with my H. Freight voltmeter and had the panel inside at a window, I couldn’t get a reliable read. Digital display would shudder from positive to (-) negative even if I switched the voltmeter’s leads. Maybe not enough voltage coming through the panel. I will try with a flashlight added to the mix, or just wait till time and weather allow for me to hall everything outside into the sun. I am just more of a plug and play when it comes to this kind of thing. I looked into swapping out the SAE for Mc4, but for one thing I have SAE everthing, a Dokio 220 kit with charge controller, a 25’ extention cable and on, and on…? Also, the kits for Mc4 don’t seem to be usable for any cables other than 10 awg to 14 awg, and my extension cable is 16 awg, which is smaller than the 14 awg. That would present another problem with Mc4 swapping. Thank you so much for your advice. I am just not wanting to destroy my EB 55 . Your kindness is appreciated. Jst
That’s kind of odd. One of my two 600 watt arrays in the backyard, in the dark, with some light from the nextdoor neighbor’s porch, is enough to give me a + or - 0.25 volts DC. I was just checking it as I rerouted the wiring, planning on installing a transfer switch. I’m looking long term to build up a system that handles all the power except my HVAC.
I did discover that just my Home Theater system uses over 300 watts. That means all the power from the battery to leave the TV for 10 hours. I’ll have to see if I can balance this out to have the ac500 charge up enough to last through the night, (I keep vampire hours - sleep all day, up all night.) 
I learn thing very quickly when one on one learning and find the way my mind works leaves most videos and even books lacking in my ability to understand the instruction. When dealing with something that can destroy my investment or set the house(in this case my van) on fire, I have a lot of questioning to do that just doesn’t happen in print or video for the most part. But, I have several videos yet to watch on my watch list, so I am not giving up. You sound far more advanced in electrical and solar things but if you need some guidance, you may want to check out this: http://www.diysolarforum.com. It is Will Prowes’ forum page and there are many links to other useful things on the home page, too. Perhaps you already know of him. I started watching his youtube years back. Thank you for all you help. I am on to the next instructional video. I am a somewhat recovering vampire, as far as sleep habits go, myself. All the best to you and thanks. Jst
Yeah, I read through a lot of info when I put together a small 1500 watt offgrid system several years ago, (back when lead acid batteries were the only way to go, which I still have, collecting dust.)
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My goal was something to keep my fridge running 24/7 in case of a long term blackout. Some $2000 later it was up and running. Fortunately I never needed it, except for a handful of short blackouts.
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Pay attention to building codes. They are there for a reason. If you burn down your house and the fire investigators find you at fault, you might not be able to collect your homeowners insurance. My solar arrays are in the yard away from my house. (Rooftop panels require permits, and the work approved by Electricians.) The wiring stayed outside where I could just run them through an open window when needed.
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On a DIY you need fuses and/or circuit breakers on almost every part of the system. Circuit breakers are actually cheaper than the heavy duty high amp fuses for the battery bank, but you need DC breakers, not AC like you find at Home Depot. There IS a vital difference. Google it.
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The solar panel arrays also need to be grounded for lightning protection, as well as fuses or circuit breakers in the wiring to your house. The support structure for my arrays are all metal, and are grounded, which includes the metal panel frames themselves.