Collyn Rivers and charging caravan batteries

Submitted: Sunday, Jan 28, 2007 at 15:45
ThreadID: 41701 Views:9951 Replies:7 FollowUps:17
This Thread has been Archived
Collyn says that most vehicle electrical systems only charge the car battery to about 70%, and that in general batteries in a caravan (deep Cycle) will only be charged to the same level unless the alternator is tweeked.

I've been running a bushman fridge of the caravan batteries and my multi meter tells me I start at around 12.7v.

I've always assumed that 12.7v would have been fully charged. I then keep the fridge on the battery until it gets down to about 11.5v.

My questions, is the battery fully charged at around 12.7v or is that only 70%? Is it ok to run it down to 11.5v?

Regards Boo Boo
Back Expand Un-Read 0 Moderator

Reply By: Mike Harding - Sunday, Jan 28, 2007 at 16:01

Sunday, Jan 28, 2007 at 16:01
I think modern vehicle electronic management systems will do a better job than 70%.

A lead acid battery is a collection of 6 cells each of which, by nature of the chemistry, have a nominal fully charged voltage of 2V1 or 12V6 for the whole battery.

Measuring the terminal voltage of a lead acid battery is not a definitive test of it's state of charge although, with a battery in good condition, it's a decent indication. If your battery is not sealed a hydrometer will provide a better indication.

It is perfectly OK to discharge a lead acid battery to 11V5 irrespective of what it's state of charge was to begin with. With deep discharge batteries it's OK to go to 11V (10V5 is the usual minimum spec) however the less you discharge a battery the longer it will last. Ensure the battery is not left in a discharged state for any length of time ie. no more than two or three days if possible.

Mike Harding
AnswerID: 218192

Follow Up By: Member - Boo Boo (NSW) - Sunday, Jan 28, 2007 at 16:05

Sunday, Jan 28, 2007 at 16:05

My vehicle is a troopy 1995.

Does that change your thoughts on whether I would get more than 70%

Regards Boo Boo
FollowupID: 478625

Follow Up By: Mike Harding - Sunday, Jan 28, 2007 at 16:18

Sunday, Jan 28, 2007 at 16:18
Not much I don't think. But why not buy a hydrometer (should only be around $5?) and test your battery after a long run in the vehicle?

It still doesn't matter what state of charge your battery is when you connect the fridge _providing_ you don't allow the battery terminal voltage to fall below 10V5 minimum (ideally 11V5) the battery will not suffer it just means it will run your fridge for less time.

Mike Harding
FollowupID: 478626

Follow Up By: drivesafe - Sunday, Jan 28, 2007 at 19:34

Sunday, Jan 28, 2007 at 19:34
Hi Boo Boo, just following on from Mikes reply, the thing you have to remember is that most people on this site will be driving their vehicles, 4x4 or car, for more that the usual shopping trolly run to the shops that most vehicles do.

As such even with older vehicles, providing your vehicle’s electrics are working correctly and your battery(s) are in good nick, there is no reason why your battery(s) can get to at least 95% charged when you go on a long trip, particularly if this is your everyday vehicle and you do at least 15 minutes driving after each start.

There is no effective way of knowing if your vehicle’s battery(s) are more that 95% charged but for most uses, 95% is sufficiently high enough to allow you to work out how much time you can expect to use your battery(s) before they need charging.

If you want to be sure of the state of your battery(s) go to a reputable auto electrician or battery sales outlet and they should test your battery(s) for free.

FollowupID: 478645

Reply By: Crackles - Sunday, Jan 28, 2007 at 19:17

Sunday, Jan 28, 2007 at 19:17
I'll go out on a limb here & say I think Colin is only partly right in that statement (& that's indeed if that is what he actually said). To make a blanket statement like that, esspecially taking into consideration all the different charging systems, battery types & sizes in all sorts of vehicles is generalizing a bit too much. I certainly have had far greater run times off my batteries than just 70% would give. For people travelling short distances a 70% charge may be close but for those driving for a full day it would have to be closer to 90%. Of course it's not practical to run regular Amp hour tests as you arrive in camp so it's difficult to prove particually as a volt meter or Hydrometer are only giving you a guide to the actual state of charge.
I supose the best way to see if your battery is at or near 100% is to use a proper 3 stage charger then measure your volts to get a base reading.
As for dropping the volts down to 11.5 yes it's OK but not ideal. The lower the volts & more often you do it the shorter the life you can expect out of the battery.
Cheers Craig...................

AnswerID: 218222

Follow Up By: geocacher (djcache) - Tuesday, Jan 30, 2007 at 22:00

Tuesday, Jan 30, 2007 at 22:00
Gees Craig,

Hope you are wearing Nomex.

Last time I criticised Collyn's advice his fan club flamed me incessantly.

Still didn't make him right though...

FollowupID: 479150

Follow Up By: Member - Boo Boo (NSW) - Wednesday, Jan 31, 2007 at 09:06

Wednesday, Jan 31, 2007 at 09:06

It definitely states in his book on Solar power for caravans that the starter battery and caravan deep cycle will only be charged to about 70%.

If thats not quite correct then I would imagine that Collyn would be happy to correct it in his next addition.

Your reply, and others I have received have helpd me a great deal. In fact the last to posts have helped immmensley. For those that read this post and helped with my water leak you will be happy to know it is FIXED.

Many thanks everyone
Boo Boo
FollowupID: 479200

Follow Up By: Member - Boo Boo (NSW) - Wednesday, Jan 31, 2007 at 09:09

Wednesday, Jan 31, 2007 at 09:09
Make that two not to., and immensely not immensley.

FollowupID: 479201

Follow Up By: Crackles - Wednesday, Jan 31, 2007 at 19:21

Wednesday, Jan 31, 2007 at 19:21
Dave, yes I was expecting a little Napalm hence "going out on the limb" but despite Collyn's vast knowledge on all things 12 volt, some of his theory's don't necessarily cover all circumstances when put into practice, like for example "starting off deep cycle batteries will wreck them in under 6 months".....I've been doing just that for almost 4 years & I'd be interested to know when I can expect mine to fail ;-)
Although simple in theory, 12 volt systems with all the variations in environment, product range, quality & design, don't always opperate the same way for everyone & is one reason it always develops plenty of healthy (often heated) discussion on this forum.
Cheers Craig............
FollowupID: 479301

Reply By: Geoff (Newcastle, NSW) - Sunday, Jan 28, 2007 at 19:34

Sunday, Jan 28, 2007 at 19:34
Hi Boo Boo,
Further to what Mike has said and something that needs to be considered is the accuracy of multimeters used to measure the battery voltage.
Some of the el cheapo's can be up to 1.5 volts out in 12 volts. Very misleading.

Landcruiser HDJ78,
Grey hair is hereditary, you get it from children. Baldness is caused by watching the Wallabies.

Lifetime Member
My Profile  My Blog  Send Message

AnswerID: 218224

Reply By: japmel - Sunday, Jan 28, 2007 at 20:43

Sunday, Jan 28, 2007 at 20:43
A fully charged Battery charging off a Solar system is actually around 14 volts.

So I guess you could say your Vehical alternateor is not fully charging your Battery.

AnswerID: 218238

Follow Up By: drivesafe - Sunday, Jan 28, 2007 at 21:52

Sunday, Jan 28, 2007 at 21:52
Hi japmel, unfortunately it’s not quite that simple.

Some alternators charge at up to 15.7 volts but these charging voltage govern more how quick the battery can be charged but have no real barring on the final voltage of a fully charged battery.

Crudely put, most batteries that are at a fully charged state will have a settled voltage of around 12.7 to 12.9 volts depending on the type battery and any voltage reading above this is only what occurs while the battery is settling, which can take up to 72 hours after the charging voltage is removed, no matter by what means they were charged.


FollowupID: 478671

Follow Up By: Angler - Monday, Jan 29, 2007 at 10:22

Monday, Jan 29, 2007 at 10:22
Most modern chargers including the automatic type charge to around 14.2 to 14.4 volts. Vehicle alternators are usually similar. After charging and left to rest the battery terminal voltage quickly drops to about 12.7 or maybe a bit more. Full charge can only be really tested with a hydrometer and the SG fully charged should be about 1275. All cells should be the same or very similar.
I have a couple of these chargers and though they each work slightly differently the end result WHILST ON CHARGE is close to 14.2 volts.
Measuring voltage means very little. An example is a recent Aux battery fail in my Patrol. Tried to winch up the boat and nothing happened at the winch. Checked the battery volts and it read 12.4V, I was on my own so I couldn't check the battery voltage under load. I run jumpers to the winch and wound the boat back on the trailer. I figured it was a problem with the vehicle wiring somewhere.
At home I checked out the anderson plug and found the same 12.4V. I then ckecked the voltage after I again plugged in the winch and switched it on to unload the boat.
The volts at the battery went to virtually zero.
I tried a charge and the battery did not take any current.
Moral of the story is never rely on a voltage check to decide on battery condition.
Incidentally the battery was on of those fully sealed calcium/calcium type about seven years old. Probably a failed cell connection caused the collapse internally.

I worked in the communications industry for some 40 years and when performing a discharge test we always stopped the test when the lowest cell voltage in the battery bank was at 1.85 volts. The capacity was then worked out and recorded.

Lead acid cells (very large ones) lasted about 10 years and Nife cells (80AH) about 40 years. Nife cells had a different cell voltage however the lowest cell reading escapes me at the moment.

FollowupID: 478715

Reply By: Member - Phil G (SA) - Sunday, Jan 28, 2007 at 22:57

Sunday, Jan 28, 2007 at 22:57
Theres a lot of variables so the battery voltage is a guide only - but its so easy to measure, that we all use it. Like Drivesafe says, 12.7 to 12.9 for most batteries.

From a practical perspective, a wet cell deep cycle battery in a remote location like a camper will always be a bit slower to charge - because the deep cycle batteries have a higher internal resistance than a cranking battery or AGM, and secondly because the long length of wiring and earth. So if you're driving a couple of hours each day, your cranking battery under the bonnet will charge up easily, but it will take a lot longer to charge the caravan's deep cycle - so it is less likely to approach full charge.
AnswerID: 218271

Reply By: mattie - Sunday, Jan 28, 2007 at 23:28

Sunday, Jan 28, 2007 at 23:28
hi BOO
i do not want steal the thead but how many amps does an inverter use to convert per 100w of 240v.
The reason i ask is that we have a xantrax charger in the camper trailer charges the battery to 13.4v and it holds it's charge very well, and charges very quick as well, after previosly owning an arlec the difference is chalk and cheese, the arlec woujd not charge to the same voltage and within a month the battery would be below 12v.
So my query is would the battery charger in the camper trailer charge my battery (deep cycle) faster with the inverter (while car is running) than using the alternator.

AnswerID: 218278

Follow Up By: Mike Harding - Monday, Jan 29, 2007 at 08:10

Monday, Jan 29, 2007 at 08:10
Try it and see?

It will be less efficient because you'll be converting 12V to 240V and back to 12V but providing the engine is running you probably won't care.

The formula for discovering the amps required for X power (watts) is:

amps = watts / voltage

so 100W / 240V = 0.416 amps
and 100W /12V = 8.3 amps

Mike Harding
FollowupID: 478696

Follow Up By: Member - Phil G (SA) - Monday, Jan 29, 2007 at 10:02

Monday, Jan 29, 2007 at 10:02
" my query is would the battery charger in the camper trailer charge my battery (deep cycle) faster with the inverter (while car is running) than using the alternator"

An alternator is capable of charging at much higher currents than chargers, particularly when the battery is discharged. But it all depends on the quality of the wiring, and the earth etc
FollowupID: 478708

Follow Up By: drivesafe - Monday, Jan 29, 2007 at 11:11

Monday, Jan 29, 2007 at 11:11
Hi Matti, as Mike pointed out, this is not only inefficient and as Phil pointed out, you only need decent size wire and the alternator will do a better job in a shorter time but even if you where to use the inverter / charger set up you would still need decent size wire and in fact you would theoretically need thicker wire because of the inefficiencies of such a set up.

To a far more important point, this type of operation is incredibly dangerous because of the potentially lethal situation that could occur as the result of your vehicles being involved in an accident.

As there is no way to make this kind of set up 100% safe in all situations, the potentially lethal position this set up can put you in is not only dangerous for yourself but it can put rescuers in unnecessary danger as well.
FollowupID: 478730

Follow Up By: Richard Kovac - Tuesday, Jan 30, 2007 at 00:29

Tuesday, Jan 30, 2007 at 00:29
Mike is there not a power factor when working out ac volts

Power(watts) = I(rms) x V(rms) x power factor or is this only for electric motors?


FollowupID: 478940

Follow Up By: Mike Harding - Tuesday, Jan 30, 2007 at 02:36

Tuesday, Jan 30, 2007 at 02:36
Indeed there is Richard but, as you say, power factor only applies for an AC supply and only with loads which have a reactive component (inductive or capacitive) motors are a typical case. Reactive loads create a phase difference between the voltage and current and mean that I = V/R no longer works accurately. Resistive loads (eg heaters) do not create this problem. Power factor normally only need be considered by electrical engineers doing load calculations. Good point though.

Mike Harding
FollowupID: 478945

Follow Up By: Richard Kovac - Tuesday, Jan 30, 2007 at 21:10

Tuesday, Jan 30, 2007 at 21:10

I'm no elecy just now some things

FollowupID: 479136

Reply By: Member - Jeff H (QLD) - Monday, Jan 29, 2007 at 23:55

Monday, Jan 29, 2007 at 23:55
Interesting thread, and thanks: a couple of names in there worth a second glance.
Would still enjoy the wisdom of Collyn on this site, eh MH?
AnswerID: 218522

Follow Up By: Mike Harding - Tuesday, Jan 30, 2007 at 02:40

Tuesday, Jan 30, 2007 at 02:40
Indeed Jeff, I was sorry to see him go, although sympathetic to his feelings, he has a good knowledge of things 12 volt and is a loss.
FollowupID: 478946

Follow Up By: Taz & Milka-Queanbeyan - Tuesday, Jan 30, 2007 at 05:02

Tuesday, Jan 30, 2007 at 05:02
Hi Folks,

Collyn was on here only a week or two ago. Rather than risk misquoting the man here are his articles for your reading pleasure:

Site Link

I posted this link several weeks ago and there were several replies describing why he no longer frequents this site and then a week or so after that I read several of his posts here.... Just trying to recall the topic ... ah yes ... it was part of the epic discussion on big tyres and aggressive treads destroying the universe. He commented on the OKA's treads ripping up the grass.

All is not lost ... perhaps there wll be a 3rd coming ??? lol

Cheers ... Taz
FollowupID: 478948

Sponsored Links

Popular Products (11)