Looking For A 36v Solar Battery Maintainer

[Sergio]

Either way would work, but I think there is quite a bit of disadvantages of running them in series:

1) Batteries need different charging rates as they don't start the same or age the same.
2) A failure of a single charger would take down the entire system.
3) A "open" failure of a single battery could take down the entire system (no current flown).
4) A "closed" failure of a single battery could damage the entire 36v bank (gassing).

Ideally each battery would have their own charger, but that is typically not economically feasible.

When it comes to multi-component system reliability where a single component can take down the entire system, the old saying:
"a chain is as strong as the weakest link" does not work, the more appropriate statement would be: "a chain is weaker than the weakest link".

Two components that have a 98% reliability in series will produce a system with 96% reliability.

You also only need 4 wires to charge 3 banks of 12v.

Since You said You are not very familiar with electronics, using 3 separate charges and hooking their individual output to 2 batteries each would probably be the easiest way.

[Rickochet]

Originally Posted by Sergio

Since You said You are not very familiar with electronics, using 3 separate charges and hooking their individual output to 2 batteries each would probably be the easiest way.

I have been into electric powered RC aircraft for years and do have some knowledge and decent soldering skills but lack knowledge on how to calculate stuff like this. I am finding a bunch of lower wattage charges pretty cheap. I am not a tight wad but keeping the investment low is preferable since it is parked in a public lot and could be subject to theft or vandalizm although that hasn't been a problem. Here is a 2.5 watt unit I found at Northern. http://www.northerntool.com/shop/too...8629_200578629

[Sergio]

Those are the "trickle charger" type to stay away from it, plus is way too little current.

You need something with an "external" charger controller as some have them built in to the cigarette plug adapter.

Here is a sample result I got from amazon, there are quite a few options, just search for the ones around 7-12watts that include an external controller.

http://www.amazon.com/ECO-WORTHY-Polycrystalline-System-Controller-Battery/dp/B00PFG56ZS/ref=pd_sbs_86_11?ie=UTF8&dpID=41%2BCuE4lRaL&dpSrc=sims&preST=_AC_UL160_SR125%2C160_&refRID=1291ZESADVCZ37J175MT

http://www.amazon.com/ECO-WORTHY-Polycrystalline-System-Controller-Battery/dp/B00PFG56ZS/ref=pd_sbs_86_11?ie=UTF8&dpID=41%2BCuE4lRaL&dpSrc=sims&preST=_AC_UL160_SR125%2C160_&refRID=1291ZESADVCZ37J175MT

[radioman]

If one of three 12 volt solar chargers failed that would upset the balance of charge on several six volt batteries and lead to early battery failures. Also three charges would require six wires to connect to three pairs of six volt or three 12 volt batteries wouldn't it?

[Rickochet]

Originally Posted by Sergio

Those are the "trickle charger" type to stay away from it, plus is way too little current.

You need something with an "external" charger controller as some have them built in to the cigarette plug adapter.

Here is a sample result I got from amazon, there are quite a few options, just search for the ones around 7-12watts that include an external controller.

http://www.amazon.com/ECO-WORTHY-Pol...SADVCZ37J175MT

I did the search for "trickle chargers" but the one I posted was listed as a battery maintainer. Apparently it has a builit in controller. What diff does it make if the controller is built in or external?

After doing more searching I am finding some external 36v controllers. I wonder if I could do three 12v solar panels in series and hook them up to a 36v controller? Another question is will a 36v solar charger take me to where I need it? I need something to take the pack to 38v?

[Sergio]

I did not know was that hard to visualize the 4 wires, but here is a simple diagram.

....+charger1-........+charger2-........+charger3-.....
|                 |                 |                 |
..+bat1-...+bat2-...+bat3-...+bat4-...+bat5-...+bat6-..

The main issue with connecting them in series is that You are not dealing with straight solar panels, but most likely PWM charging controllers or simple voltage comparator circuits.

Unless You know the internal circuit, You cannot just connect them in series.

The comment I made about the internal vs external controller was based on the circuit being inside the cigarette lighter plug, which means You cannot cut it off the circuit.

Unless You are planning on installing cigarette lighter sockets on each pair of batteries, those devices are not good solutions.

The 3 separate 12v chargers will be the most economical solution.

The best solution would be to install about +48v worth of solar panels and use an MPPT (Maximum Power Point Tracking) controller.

Those controllers can maintain the output voltage, but with varying current, regardless the amount of voltage generated by the panels.

So if there is shade in some of the panels and the voltage is only 30v, the MPPT controller will continue to generate the +36v charging voltage.

Those systems are definitely more expensive, here is a sample:

http://www.solarevsystems.com/solar-...-universal-kit

I never really tried to price or piece together a system from components, so I really don't have any "lessons learned" I can give You.

I got the impression You were not trying to "charge" the batteries, but just "maintain" the fully charged pack during the time period the cart is is not connected to power.

In that case, I would imagine the 3 x "12v solar charger with controller" would be the best option.

[Rickochet]

Thanks for the info Sergio. The units from Northern Tool come with both removeable cig lighter plugs and alligator clips so I am assuming the circuitry is inside the panel not in the cig. plug. And my goal is replace some of the energy lost during idle times not to keep them fully charged.

[radioman]

If you get low current output solar chargers in the range of 10 ma (.01 amps, .12watts) and connect them in series like I suggested (connect chargers in series and running two wires to battery pack) I don't believe you would have to worry about overcharging a healthy set of golf cart batteries. If you prefer to hook each charger to individual batteries (six connections) there would be less chance of creating individual battery charge balance in event the chargers failed or had different output voltage. JohnnieB is battery expert. Check with him. I know he has been watching.

[Rickochet]

How about if I get a single 12v solar panel with sufficient output and add a 12v to 36v boost converter and adjust it up to about 40v? A concern I have is how the 12v panel controller preset to terminate charge at whatever voltage 12 -14v(?) would react with the higher voltage of the boost converter? Would the controller keep putting out voltage until the boost converter gets to 40v?

[Sergio]

If You get an MPPT charger controller, then You can use a smaller voltage solar panel array of high wattage and the controller will boost the output voltage as needed to maintain the configured charging output

While these things are not rocket science, there are a few basic concepts that need to be understood.

If You just connect solar panels in series, the only concern is what kind of "bypass" system the panel arrays have to exclude sections of the panel that are not generating voltage.

A solar voltaic cell that is not getting sun will have a high resistance and will stop all current from flowing through the entire system.

If Your panel has a built in controller, the + and - wires coming out of it are not the output of the solar cells, but possibly the PWM of the charger or whatever unknown circuit is being used.

I have never heard of connecting solar chargers in series, the proper solution in this case is to use an MPPT controller where the solar panel voltage and the battery voltage don't need to match.

The recommended float charge voltage for a 36v Trojan pack at 77F is 39.6v, You can look up the correct voltage for your batteries and the proper temperature compensation.