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Forum Index : Solar : Bang bang solar regulator
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| beau Newbie  Joined: 07/09/2018 Location: AustraliaPosts: 4 |
Hi Folks. Been playing with solar for quite a few years now and had my fair share of different components and brands that ive used. At present I have a motorhime that uses a reconfigured Nissan leaf pack (24v 20kWh approx) My charge controller has just died and im tired of paying $300+ for stuff that just doesnt last. Ive come up with a plan that may or may not be a good idea. I have the Fangpusun bmv702 (Victron clone) It, like the Victron has the ability to switch an inbuilt relay at a set soc or voltage point. Is there any reason I cant use this relay to trigger a 200amp contactor as a crude solar charger? My panels, 7 x 250w are wired in series so.Im seeing around 60amps peak. Thoughts? |
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
It would charge the battery, but it would stuff the battery pretty quick. Doing it that way the battery would see full amps all the way till it's float setting which would ruin them. Either buy a better controller or build one yourself. I don't know if Mad's diy controllers work on 24v. Look at the second post down on this page Cheers Caveman Mark Off grid eastern Melb |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The DIY regulator works on 24V just need to change a few settings I will post them in the next day or 2. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I never thought to ask as I don't have one, but how does your controller handle lithium? Just change setpoints? Cheers Caveman Mark Off grid eastern Melb |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Presumably the leaf battery is still using parts of the original battery management system to keep the cells in balance as they become fully charged. Having a bang bang relay controlled power source just isn't going to work, the final phase of charging requires a reduction in current by using a fixed voltage source, as the current tapers off to full charge state this allows the balance's can do their job. This cannot happen if your voltage set point relay just switches off. Also switching 60 amps repeatedly with a relay will rapidly shorten its life, even if you use an evacuated relay, it won't last very long. You need a number of parallel mosfets as your switch, with pwm to limit the charge current at the full voltage set point. This means building one yourself or purchasing something off the shelf; if you get anything from AliExpress or Ebay be very wary, make sure it has at least double the rating you require, anything marketed as 60 amps is for 60 seconds not continuous. Cheers Mike |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Lithium requires much more complex management of each individual cell, so no. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| beau Newbie Joined: 07/09/2018 Location: AustraliaPosts: 4 |
Nope, not using the original leaf balancing gear. Ive never had an issue with lithium going out of balance in any setup ive had, despite the many armchair experts opinions... |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Do you want to tell the "armchair experts" how you balance then? Cheers Caveman Mark Off grid eastern Melb |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Ok, well if the individual cells were balanced initially then combined into a pack, you can use an arbitrary overall set-point voltage to determined full charge of all cells. Guess you have taken a sum of a lower cell voltage eg 3.45 per cell rather than max. I have done this on a pack of 40 AH cells for quite sometime and it worked well, however as they aged over a 3 year period the cells individual capacity changed and with a fixed end point pack voltage the cell voltages started to vary all over the place, some started to exceed the 3.6v max and if left would have eventually killed them. So yes you could risk it and bang bang with a relay, providing you re-balance individual cells say annually; you will have to spend a significant amount on a decent relay, probably near the cost of a proper controller. Best of luck.. Cheers Mike |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Batteries are not cheap and how you look after them will have a big effect on their lifespan. I am just going to sit back and watch now.  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| beau Newbie Joined: 07/09/2018 Location: AustraliaPosts: 4 |
Largest Delta I generally see is 12mv, thats under 100+a loads. Im not saying my idea of a relay based controller is the only solution. As mentioned this battery wasnt cheap. I would like to have a crack at building your reg Madness, ill have to check out your thread properly. |
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| hotwater Senior Member  Joined: 29/08/2017 Location: United StatesPosts: 120 |
When I read Bang Bang Regulator, I thought of something different. I never recommend videos, but this is worth watching. Skip to 3:40 and avoid a bunch of crap. This will make you jump out of your seat. https://www.youtube.com/watch?v=fQG1HBEUg-I&t=4s |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
That is a "SOALR" charge controller, perhaps it is not meant to be used with Solar? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
balancing is a non-issue unless something is installed wrong, its faulty or damaged I have built quite a few systems that bulk charge with staged voltage (and time) triggered contactors, up to four PV banks, they work fine. I have also added a couple of panels and a tiny controller on systems with constant small loads to "top up" in the afternoon. I'm confused, no wait... maybe I'm not... |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
That's very interesting, how is Lithium Ion and LifeP04 different though in balancing? Cheers Caveman Mark Off grid eastern Melb |
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