VERY small system

Re: VERY small system

Another way to look at the charging--Since you know the Imp is 0.57 amps and are using a PWM charge controller:

• 0.57 amps charging / 9 AH battery = 0.063 = 6.3% rate of charge

So, from a current point of view, this will charge the battery OK. You probably would want to buy a small 1 amp clip on AC battery charger so you can recharge over night rather than leaving the solar panel+battery sitting outside for two to three days to fully recharge:

• 9 AH * 0.50 max discharge * 1/0.57 amps Imp = 7.9 hours of "full noon time equivalent sun"

For much of the US, you can expect around 4-6 hours of day of sun during the non-winter seasons. You should also count on continuing the charging about another 2-4 hours to finish the battery charging (or about 2-3 days of sunny weather).

One thing to look at, many 10 watt "portable" panels do not have Vmp in the range of 17.5 to 18.6 volts or so (the optimum panel rating for use with a PWM charge controller), but instead are around 15.5 volts or less--That level of voltage is designed to connect directly to the battery for recharging (too much voltage drop for use with charge controller)--especially when the panels get hot under normal sunlight conditions (Vmp falls with heat).

Two other suggestions--You use some sort of polarized plug between panel and battery--Connecting the battery backwards to the solar panel will immediately toast the panel. And second, A DC Current Clamp meter will be much easier to measure the current in the wiring buy just clipping the current clamp around the wire--no cutting of wire/putting meter in series with the load is required. This meter from Sears is an AC/DC current clamp DMM (digital multi meter) that works pretty well.

AGM batteries can usually sit (after they been fully charged) for 1-3 months between recharging. Another way I use to "maintenance" charge a small battery + AC cube charger is to put it on a lamp timer set for around 15 minutes to 1 hour per day--That will usually keep the battery charged without over charging it (or having to remember to recharge the battery every month or so in storage).

-Billl

Re: VERY small system

As far as I know, you can easily go upwards of 25% rate of charge--And some AGMs will accept a lot more (you need to check the manual).

My suggestion would be that if you go >13% rate of charge, you have a charge controller that supports a remote temperature sensor (attached to one of the batteries in the bank). The higher the rate of charge, the more chance of thermal runaway (as batteries get hot, the charging voltage drops, which can trick the charge controller into supplying more current, batteries get even hotter--repeat). The 13% (or technically C/8 = 12.5%) is the typical flooded cell maximum charge rate without requiring active cooling/temperature sensing of deeply cycled batteries such as in a fork lift, etc.

Also note that you will probably only see high current charge rates when you discharge the bank below ~80-90% state of charge--When the batteries are over 80-90% state of charge, they normally will begin to limit the charging current. The chances of the batteries over heating are more likely the deep the discharge (or if the charge controller is miss-programed or has a fault and hits the battery bank with too high of voltage).

If you have high daytime loads (say water pumping, running computers/appliances/etc.)--Then having more panels also makes a lot of sense (and reduces the available charging current to the battery bank anyway).

-Bill

Re: VERY small system

gww1 wrote: »

Bill
Dang-it, you just gave me another reason to worry. If I hook up the battery heat sensor I have to worry about turmal run away. Gee-wiz, I can't keep up.
Cheers
gww

GWW,

It all depends (I assume you have the sentence backwards?--Thermal sensor connected to charger to limit chances of thermal run-away). Size/type of battery, depth of discharge, rate of charge by the charge controller, etc...

Always trying to be conservative when we give advice here. Short answers tend to be error on the safe side--Longer answer runs the risk of eye glaze-over.

Big systems, large amounts of stored energy, frequently unattended for hours/days/weeks at time. And sometimes operated by casual users.

Even the stuff "done by the book" still faults/fails. Why we still have circuit breakers and I recommended non-flamable construction (wall board, concrete backer board, etc.) rather the mounting on bare plywood with exposed wiring.

So learn from this one:

A three-alarm fire that damaged a San Carlos warehouse containing memorabilia belonging to rocker Neil Young started in a vintage car that he had converted into a hybrid vehicle, authorities said today.

An investigation determined that the fire started in a 1959 Lincoln Continental and spread to the warehouse. Young had outfitted the car with electric batteries and a biodiesel-powered generator as part of his company called LincVolt.
...
"We are still investigating the exact cause, although it appears to be an operator error that occurred in an untested part of the charging system," Young said. "We do know that the car has been operating perfectly for almost 2,000 miles and the system in question would not be in use while driving the car. We are investigating the components involved with plug-in charging."

www.lincvolt.com

-Bill

Re: VERY small system

The remote battery temperature sensor reduced the chance of this happening by reducing the charging voltage set point for a hot battery bank.

-Bill

Re: VERY small system

Juice to the battery is current or amps. Less than 80-90% state of charge, the battery will accept upwards of 100% of the charge controller output current.


As the battery gets towards 100% state of charge, the current will back down to about 1 to 2% of the battery's AH rating. Assuming reasonable current and voltage set points.

-Bill