76zedfour Posted October 7, 2019 Share Posted October 7, 2019 I know some of you are pretty switched on with solar power so..... I currently have a Votronic mmpt 350w controller with a single 180w panel which I only put in a few months ago. It works flawlessly but I am contemplating putting an e-motor kit on my bike and will need more solar for off grid recharging. If I double up with an identical panel this will exceed the Votronic capacity by 10w and I dont wish to particularly upgrade the controller as they are expensive. Is this a problem in terms of overloading the controller circuitry or will the controller simply cap the incoming energy at a max of 350w so a theoretical 10w is merely "lost"? I have emailed Votronic to ask but their tech guy is on hols until the 14th Link to comment Share on other sites More sharing options...
colin Posted October 7, 2019 Share Posted October 7, 2019 Are you sure you need extra? The chargers are normally around 80 or 90w , depending on when during the day and year you may find you have enough, depending on what else you use. Link to comment Share on other sites More sharing options...
76zedfour Posted October 7, 2019 Author Share Posted October 7, 2019 for spanish winters. I only wild so never on EHU. I had a 120w panel last year and it wasnt enough for my needs so i figued 180w with a quality mppt would cover my usual output and another panel would suffice for the bike. Its a Tong Seng TSDZ2 kit 48v 500w motor with a 12ah battery. I ride virtually every day so would think the battery would be less than 50% before charging every evening. Appreciate if anyone can do the maths on that and advise accordingly? Link to comment Share on other sites More sharing options...
colin Posted October 7, 2019 Share Posted October 7, 2019 AFAIK it's the maximum power they can handle, if you don't want the (unlikely) risk of damage to the controller, then you could fit a (say) 150w panel, only slightly lower output and no risks. Link to comment Share on other sites More sharing options...
76zedfour Posted October 7, 2019 Author Share Posted October 7, 2019 Long story which I wont bore you with but I already have the second 180w panel so you can see my hopeful question about the suitability of the 350w controller Link to comment Share on other sites More sharing options...
Charles Posted October 7, 2019 Share Posted October 7, 2019 For winter use they won't put anywhere near maximum power out if they're flat... Facing the sun is a different story mind. Link to comment Share on other sites More sharing options...
76zedfour Posted October 7, 2019 Author Share Posted October 7, 2019 doing my own maths here. If my bike battery is 48v 12ah then it will draw 48ah from my 12v battery bank to recharge from flat. Likely scenario will be discharged to about 1/3rd capacity so 32ah required. My quality 180w panel with the votronic mppt should be able to feed 10amps an hour in spanish winter sun so i might be ok with the single panel after all. Does that sound about right or am I mixing my watts, volts and amps? Long time since I did school physics! Link to comment Share on other sites More sharing options...
plwsm2000 Posted October 7, 2019 Share Posted October 7, 2019 You also need to take into account the inefficiencies of the battery, the various chargers in the line and loses in cables etc. It might be easier to look at this in Watt.hours rather than Volts and Amp.hours (so your 48V 12Ah battery has a capacity of 576Wh). If you are using a mains battery charger driven from an inverter, then you are probably losing around 10% of the power. If you have a battery charger driven directly from your 12V battery, then you might be losing something closer to 5%. Batteries also are not 100% charge efficient and you will lose another 2% or so which means your 576Wh batteries will need something like 645Wh to charge them from empty (+12%). For 2/3 depleted, they would need something like 430Wh to get them back to a fully charged state. Your solar regulator will also not be 100% efficient (typically around 95%) so even if you had 180W from you solar panel, this would give about 170W of useful power in perfect conditions. Realistically, this is going to be significantly less during winter when the sun is lower in the sky and 100W might be more reasonable even in Spain. Therefore on these figures, you need around 4.3 hours of continuous sun just to recharge your bike battery. You probably will also be using your solar to recharge your normal habitation battery so this needs to be added in too. Link to comment Share on other sites More sharing options...
spirou Posted October 7, 2019 Share Posted October 7, 2019 The question isn't 10W extra as much as max input voltage that could damage the regulator. For Votronic 350 duo digital I see tech specs are max solar panel voltage 50V, max panel current 21A, max charging current 26.5A Look at the data on your panels (Vmpp/Impp...) then use this handy victron calculator https://www.victronenergy.com/solar-charge-controllers#mppt-calculator to see what kind of voltage and current you can expect to see at low/high temperatures. Just ignore the specifics of victron models, look at the numbers. I suspect you'll be fine on the voltage side but could be throwing away quite a bit of extra current (as heat?). Link to comment Share on other sites More sharing options...
colin Posted October 7, 2019 Share Posted October 7, 2019 I don't think I've seen a 48v road legal bike, most now are 36v with a few 24v. We charge little and often, which is perfectly fine for the batteries, as i posted, most chargers are low output and take quite a few hours for a full charge. Link to comment Share on other sites More sharing options...
76zedfour Posted October 7, 2019 Author Share Posted October 7, 2019 Very helpful and interesting replies one and all. Thank you. Panel is a German photonicuniverse one. Namely this; Peak power: 180W Maximum power voltage: 20.2V Maximum power current: 8.91A Open circuit voltage: 23.9V Short circuit current: 9.47A I was planning to use a smallish pure sine inverter to supply the bike kits included charger. I think that 48v is legal for a bike as long as its motor is 250w max. The bolt on kit I am looking at is 500w but whoosh bikes do the same 48v one in a road legal 250w format Link to comment Share on other sites More sharing options...
spirou Posted October 8, 2019 Share Posted October 8, 2019 using the data provided I get the following results for two panels wired in series: max. PV voltage at -10°C = 54,1V max PV voltage at 70°C = 32,8V max Impp at -10°C = 8,71A max Impp at 70°C = 9,17A max output current at -10°C = 33,1A max output current at 70°C = 24,9A wired in parallel: max. PV voltage at -10°C = 27,1V max PV voltage at 70°C = 15,6V max Impp at -10°C = 17,42A max Impp at 70°C = 18,33A output current stays the same So, assuming max solar panel voltage 50V, max panel current 21A and max charging current 26.5A, you should be fine if wired in parallel, but not in series. You will be throwing away available power in those rare cases when you could actually produce the rated numbers, but the regulator should be fine. If you're worried about it, park in the shade B-) 76zedfour - 2019-10-07 9:10 PM Very helpful and interesting replies one and all. Thank you. Panel is a German photonicuniverse one. Namely this; Peak power: 180W Maximum power voltage: 20.2V Maximum power current: 8.91A Open circuit voltage: 23.9V Short circuit current: 9.47A I was planning to use a smallish pure sine inverter to supply the bike kits included charger. I think that 48v is legal for a bike as long as its motor is 250w max. The bolt on kit I am looking at is 500w but whoosh bikes do the same 48v one in a road legal 250w format Link to comment Share on other sites More sharing options...
76zedfour Posted October 8, 2019 Author Share Posted October 8, 2019 Thank you for those figures. I am a always a keen learner and tend to over analyse the little jobs i plan to do so really appreciate all this input. I had planned to link in series as my pre installed wiring I used for first panel was 4mm so as to avoid quite large amp losses in parallel from the little I understand. Those figures suggest the voltage would be over 50v at -10c which I assume is the only one outside the scope of the 350w controller. Surely that is a theoretical but not really practical scenario as I would have thought once the sun is on a panel it would be very unlikely that the surface area was at -10c in most destinations never mind in southern europe where I am likely to visit in winter. I note that other 180w panels do have a higher voltage and lower amperage than the one I chose which when paired up would produce a much higher PV voltage so maybe my panels are by their specification just about within the votronics range. Would that be a fair assessment do you think? Link to comment Share on other sites More sharing options...
spirou Posted October 8, 2019 Share Posted October 8, 2019 You can use the excel version of the victron calculator (same link above) to see all these numbers yourself. Remember the rated numbers are at normal temperatures (probably 25°C, I forget) and voltage will increase with lower temperatures. The calculation table tab in excel suggests you could go over 50V (in series) already somewhere between 10 and 15°C. This is with default temperature coefficients but it shouldn't matter too much. I don't really see how series wiring would be an option if you want to stay within the limits. Link to comment Share on other sites More sharing options...
76zedfour Posted October 8, 2019 Author Share Posted October 8, 2019 thanks. i think i will bite the bullet and change to the 430w controller. I have read on this or another forum that the german photonicuniverse panels spec is rather conservative and they can perform up to 10% better but i have never taken readings myself to verify. With a potential 400w array its not worth the risk. Anyone want to buy a votronic mppt controller just a few months old with receipt? Link to comment Share on other sites More sharing options...
mikefitz Posted October 8, 2019 Share Posted October 8, 2019 With the 430 you are still limited to 50 volts input voltage so cannot use the panels in series. Providing there are no shading issues, series operation of identical panels is the most efficient. The Victon 100/30 as an alternative controller would be suitable and it's adaptive charging perhaps more capable of correctly charging your batteries. Mike Link to comment Share on other sites More sharing options...
76zedfour Posted October 8, 2019 Author Share Posted October 8, 2019 mikefitz - 2019-10-08 12:53 PM With the 430 you are still limited to 50 volts......... Mike Very surprising. Thanks for pointing that out and saving me unnecessary hassle. Victron it is then. Link to comment Share on other sites More sharing options...
Ninjabob Posted October 11, 2019 Share Posted October 11, 2019 I think there is no reason why you could not buy a second Voltronic and have on regulator for each panel. Might be even more efficient and save the bother of maybe selling one and buying the Victron? Link to comment Share on other sites More sharing options...
76zedfour Posted October 11, 2019 Author Share Posted October 11, 2019 That did occur to me but I used the dethleffs pre installed wiring for the first panel and controller. I don't really want to put any more holes in the roof or run cable through the motorhome if I can help it. Link to comment Share on other sites More sharing options...
plwsm2000 Posted October 12, 2019 Share Posted October 12, 2019 I would check with the manufacture first before doing this. I would not be surprised in the controllers confused each other since they monitor the battery voltage and adapt their charge accordingly. As it's the same battery voltage they are measuring, one (or both) of them will probably drop the charge rate prematurely and so you will not get the maximum power from your panels. Link to comment Share on other sites More sharing options...
76zedfour Posted October 14, 2019 Author Share Posted October 14, 2019 mikefitz - 2019-10-08 12:53 PM With the 430 you are still limited to 50 volts input voltage so cannot use the panels in series. Providing there are no shading issues, series operation of identical panels is the most efficient. The Victon 100/30 as an alternative controller would be suitable and it's adaptive charging perhaps more capable of correctly charging your batteries. Mike @Mikefitz , is there any particular reason you quoted the 100/30 rather than the 75/15? I ask this because in series my panels voltage would be at most 55v and less than 10 amps and the 75/15 fits the bill or is the 2nd figure of 15 referring to the amps out rather than amps in? Link to comment Share on other sites More sharing options...
spirou Posted October 14, 2019 Share Posted October 14, 2019 The second number is amps out and you definitely need the 100/30 model. The 100/20 model would work but with limiting amps out. Link to comment Share on other sites More sharing options...
76zedfour Posted October 14, 2019 Author Share Posted October 14, 2019 many thanks spirou for fast reply. Amps out as I suspected. Is even 30amps enough then? EDIT; I think I am getting the hang of this solar thing now so will answer my own question. The most my panels can bring in is 360w. If the controller bangs that out at 14v then amperage will only be about 26a so with usual position of sun, angle of panel, ambient temp and controller and cable inefficiences then this figure is in practice is rarely going to go much above 20amps anyway Link to comment Share on other sites More sharing options...
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