Charging small lead acid battery

i Connecting it to a boat system being charged at say 15 or 20 amps might be a bit upsettling for the poor little thing.


My Ctek 5 has a maximum charge rate for small batteries of 5A. That would seem to be the sensible limit.
 
My understanding is that you cannot force feed a battery simply by connecting it to a charging source of a certain current capacity. The battery will take the current it needs. Only way to overcharge a battery is by raising the voltage too high, typically over 14.4V , or keeping that maximum voltage for too long.
I think you could safely connect your small battery to the boat system, provided that you disconnect it when on shore power or if you do very long engine runs.
 
sailorman said:
it wont like a hi amp charge as fully sealed,these are only normally trickle charged. Jump start packs do have a 240 or12v charge option
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sarabande said:
i Connecting it to a boat system being charged at say 15 or 20 amps might be a bit upsettling for the poor little thing.


My Ctek 5 has a maximum charge rate for small batteries of 5A. That would seem to be the sensible limit.
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But it wont draw a high current, like 15 or 20 amps, if the boat's charging system is regulated at an appropriate voltage.


Provided the boats system is regulated at a suitable voltage it can be safely charged on board.

I might consider charging via a Schottky diode to prevent it discharging alongside the boat's battery . Schottky rather than silicon diode for its lower voltage drop.
 
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BabaYaga said:
My understanding is that you cannot force feed a battery simply by connecting it to a charging source of a certain current capacity. The battery will take the current it needs. Only way to overcharge a battery is by raising the voltage too high, typically over 14.4V , or keeping that maximum voltage for too long.
I think you could safely connect your small battery to the boat system, provided that you disconnect it when on shore power or if you do very long engine runs.
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It wont naturally charge from the boats batteries. It will only charge when the boats own batteries are charging. ie engine running, shorepower charger on, generator on or solar/ wind active.
 
VicS said:
But it wont draw a high current, like 15 or 20 amps, if the boat's charging system is regulated at an appropriate voltage.


Provided the boats system is regulated at a suitable voltage it can be safely charged on board.

I might consider charging via a Schottky diode to prevent it discharging alongside the boat's battery . Schottky rather than silicon diode for its lower voltage drop.
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VicS said:
It wont naturally charge from the boats batteries. It will only charge when the boats own batteries are charging. ie engine running, shorepower charger on, generator on or solar/ wind active.
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But probably the best idea will be to look for a small 12 volt input charger. ie battery to battery charger. Maplin?
 
VicS said:
But probably the best idea will be to look for a small 12 volt input charger. ie battery to battery charger. Maplin?
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There doesn't seem to be an established commercial product for this, which surprises me a little. I spent ages trying to find one so I could charge a glider battery in a car. I think the best two solution are probably (a) get a proper mains-powered gel cell charger and run it from a n inverter, maybe a small coke can one or (b) pull apart a cheap jump start pack and use the 12V charging circuitry in there, since they can all be recharged from a lighter socket. I suspect that (a) will charge the battery much more effectively.
 
I have a small battery tucked away behind the switch panel to supply the VHF radio. It's charged by the normal ship's 12Vdc supply via a Schottky diode (smaller volt drop than a regular diode).
Both my engine and utility batteries are below the waterline so if they were submerged, I would still have a functioning VHF to send out a mayday.
 
Porthandbuoy said:
I have a small battery tucked away behind the switch panel to supply the VHF radio. It's charged by the normal ship's 12Vdc supply via a Schottky diode (smaller volt drop than a regular diode).
Both my engine and utility batteries are below the waterline so if they were submerged, I would still have a functioning VHF to send out a mayday.
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I've been thinking of something similar. Is your radio always fed by its own battery, or do you have a changeover switch to connect it if required?
 
wiggy said:
I know nothing about electronics. What is a shotkey diode and what do I need, oh and where from?
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Its a diode as far as you are concerned. It works like a one way valve in the same way that silicon or other types of diode work. The advantage of the Schottky diode over a silicon diode is the lower voltage drop.

Available from Maplin and other popular electronic component suppliers

http://www.maplin.co.uk/search?text=schottky&x=14&y=14


3 amp one should do but take advice from the electronics people

You take your + supply from the end marked with a silver band
 
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It seems to me that these little SLA batteries are easily killed by overcharge or by being left discharged like any ordinary lead acid battery.
I would try the schotky diode but I think I would fit a resistor to limit max charge current like 10 ohms or so. The battery will not however be charged unless the boat's battery is being charged. As said however be wary of higher voltage smart charger or charge controllers. If you do want to charge on a higher voltage charger then add more resitance and check the charge current using amps scale on multimeter. The charge current then will give an idea of charge time (best as slow as possible) but also related to how far discharged the battery is. good luck olewill
 
William_H said:
I think I would fit a resistor to limit max charge current like 10 ohms or so.
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I was wondering whether to suggest that when i was looking at details of Schottky diodes to prevent overloading the diode if the battery was significantly discharged.
 
These 'gel cell' Sealed Lead Acid ( SLA ) are used extensively as the power source for things like portable electronics abd systems requiring back-up power like alarms, they are used in small Uninteruptible Power Supplies.

Sytems for charging them and maintaining them as backup differ slightly. Frequently the charger is included in the equipment that the battery is part of.

Have a look at this page http://www.powerstream.com/SLA.htm

Ideally you need a temperature compensated, voltage limited, constant current charger. Other chargers will work but they shorten the battery life significantly.

Given that a 7-8 Ahr battery can be had for under £20 sometimes a cheap charger is just used.
 
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wiggy said:
I have a small 7ah 12v lead acid battery like this http://www.batterymasters.co.uk/mob...m-0.187-WIDE-MALE-SPADE-CONNECTIONS_1376.aspx for running my dinghy inflator.
It works really well but I'm not sure how to charge it on board, could I temporarily connect it to the boat system? At the moment it goes home to be charged with my motorbike charger.
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I used a similar battery to operate a portable bilge pump but found that the brass terminals were very fragile and wouldn't stand being used as the connecting and disconnecting points. I therefore made them permanent attachment points to wiring which was firmly cable-clamped to a plastic box which contained the battery with the connecting/disconnecting points being much sturdier plugs/sockets. Re charging I take mine home a couple of times in the season and charge from my Ctek which has a small battery option.
 
I would charge it via a one ohm, ten watt resistor.

This will protect the battery and enable it to fully charge but at a slow rate.

If you have a variable power supply, set it to 14v and 100mA and leave it to do the job.

Good luck.

Tony.
 
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