Choosing a battery... the War & Peace version!
Jan 30, 2011 13:23:15 GMT -1
Post by gerryw on Jan 30, 2011 13:23:15 GMT -1
Which battery?
The sort of battery that you might use on your kayak comes in three sizes: half brick, brick and breeze block!
Or so it seems…they add a lot of weight, are not so easy to store when connected and above all need waterproofing to survive, especially at sea. So which one do you need and how do you make the choice?
There are 5 considerations when choosing the right battery:
1. What type of battery must I use?
2. How ‘powerful’ do you need it to be?
3. How long do you need it to last between charges?
4. How do I recharge it?
5. How big and what shape is it?
Take a look through an electronic catalogue such as Maplin and you’ll find a wide range of 650 items to choose from with little guidance available for your specific need. There are metal hydride, NiCads, rechargeable lead acids etc all at wide range of prices and all with a wide range of specifications too.
Get the basics right
Common sense will help narrow down the search.
Unless you are made of money, the battery will need to be rechargeable and it will need to last long enough between charges to be useful. You wouldn’t want it to run out half way through a trip and certainly not mid flight if you are powering a GPS system from it.
Obviously it needs to handle the gear you want to run from it too. Gear that you might wish to expand in the future or change to more powerful models – think ahead.
It is these three main considerations that determine your choice.
A word on battery ratings
All batteries are rated by their storage capacity, usually in ‘mAh’ or ‘Ah’. These stand for ‘milliamp hours’ and ‘amp hours’ and simply tell you (approximately) how many amps can be supplied for how long when the battery is in proper use.
An ‘amp’ is a standard measure of electric current. The current is ‘drawn’ from the battery when in use. Think of it as the flow of water down a pipe fed from a water tank. The current will continue to flow as long as there is water in the tank. And the capacity of the tank can be measured as the rate that flows out (the current) multiplied by the time it flows.
For example, a 4Ah battery will theoretically supply 4A for one hour or 2A for 2 hours or 1A fro 4hrs etc. In fact you simply multiply the amps by the time in hours to get the rating. As there are 1000mA (milliamps) in one amp then a 2000mAh battery is the same as a 2Ah battery. It’s just that some types of battery are labeled one way and others a different way.
Note that I haven’t used the word power – to calculate power you multiply the current by the voltage eg for a small electric heater 240v x 10A = 2400Watts or 2.4kW. Or a small torch that runs at 9 volts and draws 100mA uses 900mW which is almost 1Watt.
You’ve guessed it
We’ll come to a very practical example in a short while but first back to the common sense approach.
To know what size of battery you need you first need to decide what you wish to run from it and what current those things will take from the battery. Also consider what you might wish to add in the future too.
Look at any of the specifications for the gear we use and you’ll see two ways that these things are specified. For fishfinders the spec usually states the current drawn in mA for you. For navigation lights and some other items their power consumption is stated in watts so you will have to work out the current as we saw above. Add all these results together and you’ll get the total current requirement of your kayak gear.
How long is long?
Now how long do you wish it to last? This isn’t straight forward either, I’m afraid.
If like me you go out one day at a time with a weeks break between and each session is typically 5 hours on the water (ignoring breaks) then you would think that the 5 hour figure would be the one to choose. Well, you’re partly correct – it is the main basis of your choice.
But you must not drain the battery until absolutely flat. Keep some charge in the battery as they tend not to last too long if you completely flatten them. Also some types have memory so when you recharge them multiple times they don’t get back to a full charge either. So what you thought was a 4Ah battery when you bought it may reduce to 3Ah over time if not correctly charged or used.
Finally, and most importantly when that 5hr session becomes a 7hr session because the fish are biting you will not be pleased if the fishfinder packs in just when you need it. Or if you’ve gone on past your destination and now wish to get back using a GPS you don’t want it to pack up before you are home. So the lesson here is to keep some charge in reserve for those unpredictable times. How much? Well it’s your choice but 20% as a minimum should suffice.
Another thought is how often you’ll get to recharge it. If you are away a full long weekend of three days and you cannot charge it in between sessions then you’ll need to factor this in too.
So that 5hr figure we started with is a minimum of 6hrs or more when considering these things. However, when we come to choice you’ll find that batteries aren’t made at the exact rating we might need so it’s best to go up one. My example of 6hrs might become 7hrs when I look at the exact battery I will choose.
So…
Now we have the load calculated and we have considered the time factor the battery capacity will be the multiple of the two. 6hrs at 1A will become a 6Ah battery requirement.
A practical, real example…
Let’s try and pull this all together with a practical example worked all the way through.
You’ve just bought a new MantaRay12 and you wish to add a Garmin 160C fishfinder, a navigation light and a bait tank. You are obviously well off!
Looking at the specs for the Garmin you are told that its power output is 150W (RMS). Ignore this figure as that is the power output of the transducer and not the power usage or the unit. You need to look in the manual that comes with it downloadable here
buy.garmin.com/support/manuals/manuals.htm?partNo=010-00403-00
where you find the power usage figure of 7W at 12v DC. (for fishfinders they are usually around the 5 to 10W level).
The pole mounted nav light you will build will have a bulb which is rated at 3W/12V DC and the bait tank you are building has a 12V pump running at 2W.
Now some of these you may not wish to run all the time but let’s calculate it as if you do.
The total wattage of the rig will be Garmin + Nav light + pump = 7W + 3W + 2W = 12W
Now as we saw earlier watts = voltage x current. The voltage of all these things is 12V to the current required is 12W/12V = 1A.
You plan to fish once a week for 4 or 5 hrs at a time and you will remember to recharge you battery in between. So lets take 5hrs and add 20% for a margin of safety. That now becomes 6hrs.
So the battery you need is 6hrs x 1A = 6Ah. Simple so far….now the difficult bit.
Which one?
One of the largest industrial battery companies is Yuasa. Take a look at their site here
www.yuasaeurope.com/en-gb/industrial/products/
It will become obvious that the most suitable battery that can handle rough(ish) treatment, is flexible in use, can handle high discharge levels and is maintenance free is the sealed lead acid battery. Other types can be used such as NiCads but you would need a number of them to make up the capacity. They would need to be housed in a special holder which serves to connect them and they are renowned for ‘memory’ where over time they loose their charging ability and therefore capacity.
Small lead acids are used for standby situations such as alarms and lighting and so you may find that there is a choice of physical shapes or sizes depending on the ‘Ah’ size you need. In our case the 7Ah version comes in small brick size ie 151 x 98 x 65mm and weighs the same as a bag of sugar (2.3Kg).
At this point you might wish to review the kit you use to cut down on size. For example leave off the nav light (fish daylight only or use a small led strap on light for emergencies). Don’t build a bait tank or change back to a mono fishfinder which use less power than a colour version. The Garmin 160C alone gets you back to 0.58A for 6 hrs plus the 20% safeguard which comes to 4.2Ah rated battery which is smaller at 90x70x100mm and lighter too at 1.6kg. Not much but you’ve got to paddle it about for 5 hrs remember. It all adds up!
Recharge it!
Small lead acid batteries don’t take kindly to a standard 12v car battery charger. They simply try to push too much charge through the battery too quickly. What you will need is a trickle charger. Quite often these are sophisticated devices which measure the state of the battery charge and give an optimum charge level to get the best from the battery.
In any event don’t forget to recharge after use and that they can be left on charge for the whole week between trips. In that case don’t then forget to take it with you!
Stow it…
In my experience this causes the biggest headache in using batteries onboard your kayak.
Best practice is to choose its location first. That may pick itself depending on hatch access etc. You don’t want it moving and banging about down there to startle the fish either and it needs to be in a watertight package otherwise salt water will short it out in no time and your kayak will be filled with a nice warming mixture of flammable hydrogen and air!
Best bet is to take it or its measurements to one of those pound shops, kitchenware shops or Tesco etc and try to find a sealable food container that will hold it. Don’t worry about it being too big – you can pack it out with camping mat (doesn’t absorb water) or bubblewrap. Access to the terminals can be via a B&Q gland for under a pound so allow a little extra room to fit that too.
With a bit of ingenuity the food container with battery can then be slung round a scupper hole pillar or two using velcro elastics, cable ties or gaffer tape depending on your patience.
Where to buy?
Well Ebay of course. Maplin might be convenient but you’ll easily pay a teener more there than on Ebay. And they sell branded items there too. Lucas is a good make at a reasonable cost. While you’re there pick up the charger too for a song.
So there we are. Longwinded I know but I hope that it will help you choose the right battery and get the best from it.
Cheers
Gerry
The sort of battery that you might use on your kayak comes in three sizes: half brick, brick and breeze block!
Or so it seems…they add a lot of weight, are not so easy to store when connected and above all need waterproofing to survive, especially at sea. So which one do you need and how do you make the choice?
There are 5 considerations when choosing the right battery:
1. What type of battery must I use?
2. How ‘powerful’ do you need it to be?
3. How long do you need it to last between charges?
4. How do I recharge it?
5. How big and what shape is it?
Take a look through an electronic catalogue such as Maplin and you’ll find a wide range of 650 items to choose from with little guidance available for your specific need. There are metal hydride, NiCads, rechargeable lead acids etc all at wide range of prices and all with a wide range of specifications too.
Get the basics right
Common sense will help narrow down the search.
Unless you are made of money, the battery will need to be rechargeable and it will need to last long enough between charges to be useful. You wouldn’t want it to run out half way through a trip and certainly not mid flight if you are powering a GPS system from it.
Obviously it needs to handle the gear you want to run from it too. Gear that you might wish to expand in the future or change to more powerful models – think ahead.
It is these three main considerations that determine your choice.
A word on battery ratings
All batteries are rated by their storage capacity, usually in ‘mAh’ or ‘Ah’. These stand for ‘milliamp hours’ and ‘amp hours’ and simply tell you (approximately) how many amps can be supplied for how long when the battery is in proper use.
An ‘amp’ is a standard measure of electric current. The current is ‘drawn’ from the battery when in use. Think of it as the flow of water down a pipe fed from a water tank. The current will continue to flow as long as there is water in the tank. And the capacity of the tank can be measured as the rate that flows out (the current) multiplied by the time it flows.
For example, a 4Ah battery will theoretically supply 4A for one hour or 2A for 2 hours or 1A fro 4hrs etc. In fact you simply multiply the amps by the time in hours to get the rating. As there are 1000mA (milliamps) in one amp then a 2000mAh battery is the same as a 2Ah battery. It’s just that some types of battery are labeled one way and others a different way.
Note that I haven’t used the word power – to calculate power you multiply the current by the voltage eg for a small electric heater 240v x 10A = 2400Watts or 2.4kW. Or a small torch that runs at 9 volts and draws 100mA uses 900mW which is almost 1Watt.
You’ve guessed it
We’ll come to a very practical example in a short while but first back to the common sense approach.
To know what size of battery you need you first need to decide what you wish to run from it and what current those things will take from the battery. Also consider what you might wish to add in the future too.
Look at any of the specifications for the gear we use and you’ll see two ways that these things are specified. For fishfinders the spec usually states the current drawn in mA for you. For navigation lights and some other items their power consumption is stated in watts so you will have to work out the current as we saw above. Add all these results together and you’ll get the total current requirement of your kayak gear.
How long is long?
Now how long do you wish it to last? This isn’t straight forward either, I’m afraid.
If like me you go out one day at a time with a weeks break between and each session is typically 5 hours on the water (ignoring breaks) then you would think that the 5 hour figure would be the one to choose. Well, you’re partly correct – it is the main basis of your choice.
But you must not drain the battery until absolutely flat. Keep some charge in the battery as they tend not to last too long if you completely flatten them. Also some types have memory so when you recharge them multiple times they don’t get back to a full charge either. So what you thought was a 4Ah battery when you bought it may reduce to 3Ah over time if not correctly charged or used.
Finally, and most importantly when that 5hr session becomes a 7hr session because the fish are biting you will not be pleased if the fishfinder packs in just when you need it. Or if you’ve gone on past your destination and now wish to get back using a GPS you don’t want it to pack up before you are home. So the lesson here is to keep some charge in reserve for those unpredictable times. How much? Well it’s your choice but 20% as a minimum should suffice.
Another thought is how often you’ll get to recharge it. If you are away a full long weekend of three days and you cannot charge it in between sessions then you’ll need to factor this in too.
So that 5hr figure we started with is a minimum of 6hrs or more when considering these things. However, when we come to choice you’ll find that batteries aren’t made at the exact rating we might need so it’s best to go up one. My example of 6hrs might become 7hrs when I look at the exact battery I will choose.
So…
Now we have the load calculated and we have considered the time factor the battery capacity will be the multiple of the two. 6hrs at 1A will become a 6Ah battery requirement.
A practical, real example…
Let’s try and pull this all together with a practical example worked all the way through.
You’ve just bought a new MantaRay12 and you wish to add a Garmin 160C fishfinder, a navigation light and a bait tank. You are obviously well off!
Looking at the specs for the Garmin you are told that its power output is 150W (RMS). Ignore this figure as that is the power output of the transducer and not the power usage or the unit. You need to look in the manual that comes with it downloadable here
buy.garmin.com/support/manuals/manuals.htm?partNo=010-00403-00
where you find the power usage figure of 7W at 12v DC. (for fishfinders they are usually around the 5 to 10W level).
The pole mounted nav light you will build will have a bulb which is rated at 3W/12V DC and the bait tank you are building has a 12V pump running at 2W.
Now some of these you may not wish to run all the time but let’s calculate it as if you do.
The total wattage of the rig will be Garmin + Nav light + pump = 7W + 3W + 2W = 12W
Now as we saw earlier watts = voltage x current. The voltage of all these things is 12V to the current required is 12W/12V = 1A.
You plan to fish once a week for 4 or 5 hrs at a time and you will remember to recharge you battery in between. So lets take 5hrs and add 20% for a margin of safety. That now becomes 6hrs.
So the battery you need is 6hrs x 1A = 6Ah. Simple so far….now the difficult bit.
Which one?
One of the largest industrial battery companies is Yuasa. Take a look at their site here
www.yuasaeurope.com/en-gb/industrial/products/
It will become obvious that the most suitable battery that can handle rough(ish) treatment, is flexible in use, can handle high discharge levels and is maintenance free is the sealed lead acid battery. Other types can be used such as NiCads but you would need a number of them to make up the capacity. They would need to be housed in a special holder which serves to connect them and they are renowned for ‘memory’ where over time they loose their charging ability and therefore capacity.
Small lead acids are used for standby situations such as alarms and lighting and so you may find that there is a choice of physical shapes or sizes depending on the ‘Ah’ size you need. In our case the 7Ah version comes in small brick size ie 151 x 98 x 65mm and weighs the same as a bag of sugar (2.3Kg).
At this point you might wish to review the kit you use to cut down on size. For example leave off the nav light (fish daylight only or use a small led strap on light for emergencies). Don’t build a bait tank or change back to a mono fishfinder which use less power than a colour version. The Garmin 160C alone gets you back to 0.58A for 6 hrs plus the 20% safeguard which comes to 4.2Ah rated battery which is smaller at 90x70x100mm and lighter too at 1.6kg. Not much but you’ve got to paddle it about for 5 hrs remember. It all adds up!
Recharge it!
Small lead acid batteries don’t take kindly to a standard 12v car battery charger. They simply try to push too much charge through the battery too quickly. What you will need is a trickle charger. Quite often these are sophisticated devices which measure the state of the battery charge and give an optimum charge level to get the best from the battery.
In any event don’t forget to recharge after use and that they can be left on charge for the whole week between trips. In that case don’t then forget to take it with you!
Stow it…
In my experience this causes the biggest headache in using batteries onboard your kayak.
Best practice is to choose its location first. That may pick itself depending on hatch access etc. You don’t want it moving and banging about down there to startle the fish either and it needs to be in a watertight package otherwise salt water will short it out in no time and your kayak will be filled with a nice warming mixture of flammable hydrogen and air!
Best bet is to take it or its measurements to one of those pound shops, kitchenware shops or Tesco etc and try to find a sealable food container that will hold it. Don’t worry about it being too big – you can pack it out with camping mat (doesn’t absorb water) or bubblewrap. Access to the terminals can be via a B&Q gland for under a pound so allow a little extra room to fit that too.
With a bit of ingenuity the food container with battery can then be slung round a scupper hole pillar or two using velcro elastics, cable ties or gaffer tape depending on your patience.
Where to buy?
Well Ebay of course. Maplin might be convenient but you’ll easily pay a teener more there than on Ebay. And they sell branded items there too. Lucas is a good make at a reasonable cost. While you’re there pick up the charger too for a song.
So there we are. Longwinded I know but I hope that it will help you choose the right battery and get the best from it.
Cheers
Gerry
