Author Topic: Cheap 36 volt charge controller (Read 12074 times)

madlabs · « **on:** July 07, 2012, 11:01:36 AM »

Hi All,

I have a golf cart with a 36 volt battery bank that I use as my ranch utility EV. I need a 36V charge controller good for 3.5 amps or so. I can't seem to find any cheapo charge controllers in this voltage. I may be changing the voltage of the cart in the not too distant future so I am looking for an inexpensive option.

Thanks!

Jonathan

dnix71 · « **Reply #1 on:** July 07, 2012, 11:42:13 AM »

http://www.ebay.com/itm/180W-24V-36V-48V-Lithium-Ion-LiFePO4Ebike-kit-socket-golf-cart-battery-Charger-/320940086017?pt=LH_DefaultDomain_0&hash=item4ab9851301

You tell him the voltage and battery type and he makes it your way.

Less money here: 3 amps for lithium batteries, but would probably work.

http://www.ebay.com/itm/36V-3A-Charger-for-Lithium-Battery-Packs-Aluminum-Case-/120855940443?pt=Battery_Chargers&hash=item1c23934d5b

2.5 amp charger, cheap:

http://www.ebay.com/itm/36V-3-prong-round-plug-battery-charger-2-5amp-110v-/380161946531?pt=LH_DefaultDomain_0&hash=item58836af3a3

Or you could get 2 of the standard 1.5 amp chargers for less than $20 each and parallel them for 3 amps max.

I just bought a 4 amp 24v charger for my eBike. It gets it done quick. Well worth the money spent.

madlabs · « **Reply #2 on:** July 07, 2012, 11:56:49 AM »

Oops, I wasn't clear. I need a solar charge controller. I have 3 * 55 watt panels in series that I am using to charge.

Thanks and sorry for not being clear. What, you can't read my mind?!

Jonathan

XeonPony · « **Reply #3 on:** July 07, 2012, 01:56:53 PM »

Why not get a tristar 45 mppt, they will do the whole range from twelve to 48, now you have a quality unit that you simply program the voltage you want when you switch over? most half descent quality units can manage that now days!

dnix71 · « **Reply #4 on:** July 07, 2012, 05:45:47 PM »

Yeah, I see your problem now. 12-24v mppt controller are cheap. 36v and up not at all cheap.

http://www.affordable-solar.com/store/solar-charge-controller/xantrex-c40-charge-controller
http://www.wholesalesolar.com/products.folder/controller-folder/xantrexC40.html

$120 Add one battery to the string for charging purposes and use a Schneider (Xantrex) C-40

madlabs · « **Reply #5 on:** July 08, 2012, 12:20:16 AM »

Well, if I did buy a controller as nice as either of those I would use it on my main bank/array.

I am actually planning on doing that soon. As to adding batts, maybe. I have thought of boosting it to 48V. But it won't be easy to shoehorn two more batteries in there.

However, for this situation I may have to whip up something. With the low current involved I could even dig up and modify an old DIY MMPT experiment of mine. I was just hoping to keep this project simple and cheap. Sigh. Seems like simple and cheap are never in my vocabulary!

Thanks anyhoo guys.

Jonathan

dnix71 · « **Reply #6 on:** July 08, 2012, 02:04:55 PM »

http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Solar-Converters-MPPT-Charge-Controllers/Solar-Converters-PT-36-5A-36V-MPPT-Charge-Controller/p1380/

$105 simple brick MPPT charge controller, 36v nominal operation only. Up to 5 amps.

Volvo farmer · « **Reply #7 on:** July 08, 2012, 03:24:20 PM »

I would bet that you don't even need a charge controller for 3.5 amps on six golf cart batteries, I bet you couldn't even push the voltage up to 2.4 volts per cell on an already full bank. At the very worst, they might use a little water, but I bet you could not overcharge that bank with 3 55W panels.

dnix71 · « **Reply #8 on:** July 08, 2012, 09:33:25 PM »

Volvo Farmer you may be right. I double up my panels for the benefit of my MPPT, but the max voltage is in the mid 40's in full sun. My bank is 12v, but with a 36v bank I wouldn't need an MPPT.

Madlabs, what are your panels rated and what do you get without the controller? Golf cart batteries are made to be cooked a bit after being discharged. Distilled water may be cheaper than an MPPT now.

madlabs · « **Reply #9 on:** July 09, 2012, 10:47:22 AM »

All,

I'm not hung up on it being an MPPT contoller, but of course I'd love one. The usage profile of the cart is usually a bunch on one day and then nothjing for a few days. I also work 48 hour shifts, so it just sits. I just want to make sure I don't cook 'em during the down days.

Maybe I'll make something or maybe I'll buy the one dnix linked. Or maybe I'll let 'em cook!

Thanks for the help folks!

Jonathan

Volvo farmer · « **Reply #10 on:** July 09, 2012, 03:35:38 PM »

If you run those batteries down to 50%, say about 110ahr, it's going to take over thirty hours of full sun to recharge them. Most battery MFGs also suggest a charge rate of c/10 or so, you'd want 22 or so amps into those batteries to charge them correctly, and you're charging them with 3.5A. I think you risk electrolyte stratification and sulfation more than you risk overcharging.

madlabs · « **Reply #11 on:** July 11, 2012, 04:10:42 PM »

Volvo,

On the days I use it a lot I have a 30 amp plug in types charger. So I do use that to replace big amounts of charge. The thing is that then I need to run the genny, as otherwise I'm just pulling the power out of my main battery bank.

What I really need to do is buy a charge controller that can do both a 12 and 36 volt bank, then a simple relay could determine charge destination.

Jonathan

Volvo farmer · « **Reply #12 on:** July 11, 2012, 08:35:20 PM »

You want to charge a 12 volt bank with the three 55W solar panels when you are not charging the golf cart panels?

Bruce S · « **Reply #13 on:** July 12, 2012, 10:02:10 AM »

madlabs;
You could send Ghurd a note/PM he's reconfigured his dump load controller for 48V in the past.
Just a thought.
Bruce S

madlabs · « **Reply #14 on:** July 12, 2012, 10:24:54 AM »

Volvo,

Well, yes, I would like to use the 3 panels currently wired for 36V on my 12V system. But just as much, I'd like my 660 watts of 12V wired solar panels to be able to charge the cart. It would be nice to have them all in one array and then direct the charge where it is needed. Often my battery bank is full by 2pm, so it would be nice to be able to easily direct the otherwise wasted juice to the cart.

Bruce, I'll look into Ghurds duimp controller. It can be used as a charge controller?

Thanks!

Jonathan

Bruce S · « **Reply #15 on:** July 12, 2012, 11:00:52 AM »

madlabs;
More of the dump load type than controllers similar to say a morningstar TS-60 or TS-60mppt.
You could also build one up for yuor 12V system, then when it goes into dump or however you control your system, then allow it to divert to a system for charging your cart.
however I have and continue to use a couple of these in gang format to divert my little <200watt system to charge different battery bank sizes and chemistries.
I did for a while use 4 of them the charge our daughters 48V e-bike, using one on each battery directly from NiCd battery bank.
NOTE: e-bike still works, just parked while she's away.
Might shoot him a PM / email see what he can cook up.

ghurd · « **Reply #16 on:** July 12, 2012, 06:36:47 PM »

Jonathan,
Shoot me an email if you like.
I probably have the parts to do it here.

It can be used as a solar controller, without a dump load.

Basically, it shorts the solar panel and lets the amps run in circles.
Because the solar amps never make it into the battery, there is no need to dump from the battery.

It is sort of Old School thinking in the US and maybe/probably would have code issues with anything grid tied?
It is still a common type of controller in the UK, etc, where they don't use split phase with a grounded neutral (if I phrased that correctly).

It will not harm the panels.
The current flowing through them will only be a couple percent more than into a low battery.

I could figure the part values for you. Should have them here.
There will be some parts standing up flying above the PCB. It'll look just as pretty as every other when the cover is on the box!

I don't know if I have a fet suited for it here. What I would recommend probably costs $12 with their outrageous S&H for 1 TO-220.

Might be able to parallel 2 or 3 more common (alternate spelling: 'cheaper') fets, and use gate balast resistors (free). I am basically against parallel fets, but this setup wouldn't have some of the issues in other setups.

A couple sketches for the 12V version, and a 3rd party link you say? OK, just for you.

This was for 3 smaller PVs, which could use 6A diodes,

This was for larger PV, and a much larger PV, and it shows paralleled fets on the much larger.
I recommended using bridge rectifiers as blocking diodes in his situation.

And a link with pics.
Yours would be about the same, except for maybe the blocking diode and the extra parts flying above the PCB.
The function would be the same.
http://www.fieldlines.com/index.php/topic,129703.0.html

I disagree with 3.5A not being able to overcharge golf cart batteries.
I have seen a lot of fairly new (less than 6 month old) Trojan 85 and 110AH class batteries ruined with 1.96A PVs (the old 32W Unisolar) and no controller.
I basically got a business started based on that fact. I ordered an SG-4 for a friend, then a couple for his friends, then a bunch of their friends, then people started asking for better PVs...
And this is the snow belt of NE OH. Our BEST month solar insolation is not as good as some places WORST month.
G-

madlabs · « **Reply #17 on:** July 12, 2012, 07:03:36 PM »

Thanks everybody, I appreciate the help!

Ghurd, I probably have a lot of the parts here too, including some decent low RDSON fets. I can make circuit boards too if need be. I'll take a look at what I have laying around.

I have two 330 watt arrays feeding into the main bank now. In reality they never put out much over 20 amps, maybe 23-24 on a good day. Think your controller could be scaled to do that? Currently I have a simple relay on a controller I made, takes the bank to 14.4V and then shuts one array off for a few minutes, then does it all over again. Dirt cheap but it isn't too nice on my batteries.

I will shoot you a PM and thanks for the kind offer of help. I have the local VFD BBQ to prep for this weekend so I'm going to be busy through Sunday. It's our 55th year! :-)

Jonathan

edit: Just went and looked and I have four of the very fet shown on your info page, the IRFZ44! Sahweet!! Now I'll look at the other parts.

ghurd · « **Reply #18 on:** July 13, 2012, 08:27:37 AM »

I would NOT use IRFZ44N for a 36V system.
Vdss = 55V.
3 of 12V panels in series can go past 70V.

If everything stays properly connected, 55V is enough.
BUT we know that is not how it work in the real world.

With the low amps, I think you could use IRF540.
100V, 0.044 ohm.
G-

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Author Topic: Cheap 36 volt charge controller (Read 12074 times)