solar charger needs diode

[strokersquid]

i got a 1.25 watt solar panel to charge an Arima with 2 batteries. it has no diode so at night there is a chance it could reverse charge and drain the battery(s). anybody know what diode to use or how to calculate which one ? i see lots of diodes on ebay rated for 16-18 volts but only 1 amp. can i use two in parallel ? if i put the panel + to the + terminal of one battery and the - to the - terminal of the other and a jumper between the + and - of the two batteries would it charge both ? this is only to maintain the battery at the storage lot, not to charge a flat battery.

 

[04fxdwgi]

Re: solar charger needs diode

i got a 1.25 watt solar panel to charge an Arima with 2 batteries. it has no diode so at night there is a chance it could reverse charge and drain the battery(s). anybody know what diode to use or how to calculate which one ? i see lots of diodes on ebay rated for 16-18 volts but only 1 amp. can i use two in parallel ? if i put the panel + to the + terminal of one battery and the - to the - terminal of the other and a jumper between the + and - of the two batteries would it charge both ? this is only to maintain the battery at the storage lot, not to charge a flat battery.

1.25 watt is only a 10th of an amp at 12.5 VDC (1 amp diode is plenty for your charger), but you can put as many diodes in parallel as you want, to increase current capacity of the diodes. You need to consider that if 1 battery does fail on it's own, connected to the 2nd battery, it will pull down the good one with it and the 10th of an amp charge won't keep up with the discharge. I would use 2 seperate solar chargers, one for each battery. I use a dual station "maintainer" charger (one circuit for each battery), but do have the availability of power available next to the boat.

 

[Silvertip]

Re: solar charger needs diode

Unless these batteries are AA size NiCd or NiMH that charger is nothing more than a "green energy label" and nothing more. 1/10th of an amp is not a charger and would not keep one battery topped off after being fully charged, much less two of them. That unit would not actually charging anything -- it simply does not have enough output. In comparison, I have a 7 watt panel in the window of my shed that keeps my garden tractor battery topped off. Unless there is something about this setup that you aren't telling us, you wasted your money. But -- if you really intend to use this panel, go to Radio Shack and for about 75 cents buy any diode with a PIV (peak inverse voltage) higher than 13 volts. Most of those will be in the 1 amp range and will be 10 times the current you need.

 

[strokersquid]

Re: solar charger needs diode

that's about the same output as a standard trickle charger puts out in maintainance mode. i have used them f0r years on some cars i drive infrequently, and have not needed to replace a battery since. in the past this was a frequent occurence.

 

[Silvertip]

Re: solar charger needs diode

Battery maintainers are typically in the 1 - 1-1/2 AMP range. Your solar panel is 1-1/2 WATT. They ain't the same animal. To do the same job a "maintainer" does, you would need a solar panel with around 18 watts of output. To put the difference in perspective, a 1.5 AMP maintainer will light an automotive tail light bulb. Your 1.5 WATT solar panel will not even cause a flicker on the same bulb.

 

[strokersquid]

Re: solar charger needs diode

but do those maintainers always put out 1 amp ? or are they capable of it but most of the time run at 50ma or so for maintainance ? if it were necessary to put out 1 amp to maintain a battery, then a typical 20 amp-hr jetski battery would not last a day. my 500 amp-hr starting battery for the boat would last only about 20 days. once a battery is fully charged it does not take an amp an hour to maintain it. it probably does take at least that to charge a battery, but i am not charging, just maintaining the charge.
anyways, i bought some 1n914 diodes at Radio Shack, since they were the only ones i could find between three stores. they have a peak working reverse voltage of 75 volts ( which i presume is far more than i will ever need ) , an average forward current of 75 ma ( which means that at a possibility of 1.25 watts full charge i will have 100ma so will need two in parallel ) or did i calculate wrong ?

 

[Silvertip]

Re: solar charger needs diode

No - the maintainer does not output 1 amp or 1.5 amp constantly and neither will your solar panel output it's full capacity all the time. The operative word here has been "charge". There is a difference between charging a battery and maintaining it. If either of those two batteries are down in capacity by 1 amp for example, it would take well over 10 hours to replace that current. That's two days since half the time the panel sees darkness. We have no idea what type of service these two batteries perform and if they have a way of being charged separate from the panel, so lacking that information further discussion will be a waste of both our time. The diodes will work.

 

[strokersquid]

Re: solar charger needs diode

thanks i will try the diodes. since i already have the panel, i might as well try it. what's the worst that can happen if the diodes are wrong ? will the diodes fry ( they're cheap ) ? or can i damage the panel ? you are right that all i can do here is slow down the rate of decline of the battery charge, n0t keep it in full charge.

 

[Silvertip]

Re: solar charger needs diode

If there is no fuse in the POS lead from the panel (at the battery -- not the panel) an internal short in the panel would fry the wiring and burn down whatever this panel is attached to. You want the fuse closest to the battery since it's job is to protect the wiring going to the panel -- not to protect the panel itself. Obviously if the panel has a problem that pops the fuse it is toast anyway.

 

[strokersquid]

Re: solar charger needs diode

good point, had not thought of that but that is why i reaD here. it is interesting that the large expensive 5 watt panels i have do not seem to have fuses, though it appears they have diodes. also, the smaller panels have cigaret lighter plugs that have diodes and fuses, but if you use the leads that clip directly on to the battery, you do not get neither.