20 Amp dc/dc charger

Submitted: Friday, Aug 12, 2016 at 08:33
ThreadID: 133202 Views:3166 Replies:9 FollowUps:5
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Hi , looking for advice .I have a 20 Amp dc/dc charger installed in my LC 80 series charging a 105 Agm DC battery , I would like to add a second battery in parallel with the same specs to this set up, , any one's thoughts ? , cheers.
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Reply By: gbc - Friday, Aug 12, 2016 at 09:17

Friday, Aug 12, 2016 at 09:17
Your user guide will tell you what your existing charger will do. Most 20a dc chargers like the ctec 250 will administer to up to 300ah of battery bank. 210 ah should be bread and butter for most of them.
AnswerID: 603323

Reply By: Allan B (Member, SunCoast) - Friday, Aug 12, 2016 at 10:03

Friday, Aug 12, 2016 at 10:03
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Hi Marty,

It would be quite OK to connect a parallel battery of the same type but bear in mind that your charger will only deliver a maximum of 20A to be shared by the batteries.
You will have doubled your storage capacity but not your charging.
Cheers
Allan

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AnswerID: 603328

Reply By: Member - Roachie - Friday, Aug 12, 2016 at 15:05

Friday, Aug 12, 2016 at 15:05
I had a Redarc 1220 DC-DC charger in my last rig (Landcruiser) and used it to charger 2 AGM batteries of different brand, age and capacity. One was a 120a/h Fullriver I bought around 2002/3 and the other was a 100a/h Redback that I bought in 2010.

The Redarc handled the charging duties quite okay and I never had ANY issues whatsoever.

The batteries had the job of running my 40 litre Engel 24/7/365 as well as occasional air compressor work etc.

Roachie
AnswerID: 603341

Reply By: swampy - Friday, Aug 12, 2016 at 20:46

Friday, Aug 12, 2016 at 20:46
HI
Just make sure u have at least b&s cable feeding the charger .
No need to buy a different unit till the current one dies . At that point it maybe worth considering a larger charger 30-40 amp .

swamp
AnswerID: 603349

Reply By: marty d - Saturday, Aug 13, 2016 at 03:10

Saturday, Aug 13, 2016 at 03:10
Thank's for replies , Roachie I may be in the same boat as you were ! . Instead of scoring a Fullriver 105dc , my mate has given me a 120ah Fullriver dc , all the same except amperage . I tried it out a bit with my shed based 20amp and 2.7 amp standard chargers and couldn't detect any voltage or temperature issues , smart charger might not like it though ? , cheers.
AnswerID: 603353

Follow Up By: Member - Roachie - Saturday, Aug 13, 2016 at 19:32

Saturday, Aug 13, 2016 at 19:32
I always keep my batteries in fully charged condition. At home the truck is always plugged in to 240v power supply (to run fridge and charge batteries via 25 amp charger). When traveling I rely on the DC-DC charger, although my new truck also has a pair of solar panels on the canopy.

When I sold the Landcruiser earlier this year it still had the Fullriver 120a/h battery installed and was still doing its job after more than 13 years.

Look after your battery/ies and they'll look after you ....that's been my experience over the past 30+ years

Roachie
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FollowupID: 872990

Reply By: Alloy c/t - Saturday, Aug 13, 2016 at 09:41

Saturday, Aug 13, 2016 at 09:41
Most batteries like a charge 'rate' of 10% [or a little less] of their capacity so a 20amp charger is right on the money for the capacity you have envisioned , any bigger as in a 30/40 amp charger will of course charge the batts a bit quicker BUT at the detriment of battery longevity…...
AnswerID: 603358

Follow Up By: Allan B (Member, SunCoast) - Saturday, Aug 13, 2016 at 16:09

Saturday, Aug 13, 2016 at 16:09
Alloy, the specification of "10% charge rate" may have been true for the old unregulated chargers but today, with multi-stage chargers, the general consensus of battery makers is a current (A) of 0.2 x C (battery capacity). This of course varies somewhat across battery types and manufacturers but is typical.

Marty says he is using a dc-dc charger so I would reasonably presume it is multi-stage. Further, he has Fullriver AGM's and Fullriver state..... "The initial charge current is recommended to be set at 0.20 x C".... which would allow Marty to charge at up to 20A max per battery. He may not need to, depending on his load demands and available charging times, but he has that option if needed.
Cheers
Allan

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Reply By: marty d - Saturday, Aug 13, 2016 at 09:46

Saturday, Aug 13, 2016 at 09:46
Thank's Swampy , yes ive used 6 gauge B@S wiring throughout , ive also used a manual reset on/off type circuit braker .
AnswerID: 603359

Follow Up By: Allan B (Member, SunCoast) - Saturday, Aug 13, 2016 at 12:04

Saturday, Aug 13, 2016 at 12:04
.
Marty, it is good to see that you have used "manual reset" circuit breakers. Those self-reset breakers are not a good idea. If there is a short circuit they simply continue to reclose until either a) the cable melts the insulation, b) the battery goes flat, or c) the breaker self-destructs. Furthermore, I have yet to see a 12V one that I would consider to be of good quality.

Self closing breakers at any level of engineering are intended to protect a simple overload such as connecting an appliance who's load exceeds the supply capability whereupon you would observe that and disconnect the load. They are not appropriate for short-circuit protection where a fuse or manual-reset breaker should be used.
Cheers
Allan

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FollowupID: 872985

Reply By: swampy - Saturday, Aug 13, 2016 at 18:03

Saturday, Aug 13, 2016 at 18:03
HI

charge rate of AGM
20-30% of capacity 20-30 amps per 100ah of battery

charge rate of flooded [wet cell]
10- 20 % of capacity 10-20 amps per 100ah of battery

The charge rates are typically higher for AGM than wet flooded .
This is an advantage for Agm style of batteries ,why not take advantage of it .
In saying that apparently Agms have a small amount of fluid so not ""amping up"" to the max would be a precaution and with correct voltages to prevent fluid boil off . The lower regions of say 20-25 % would be good idea .

Always refer to battery makers instructions .
Not all chargers are ideal for all batteries all the time .

A lower amp charger will just take a lot longer
EG at 15 amps charge rate ,a lot of time will be needed to recharge say 100ah at that rate via a dc to dc 8-9 hours . Or at 25 amps 5-6 hrs

swamp
AnswerID: 603363

Follow Up By: Alloy c/t - Sunday, Aug 14, 2016 at 09:46

Sunday, Aug 14, 2016 at 09:46
If you have depleted your batts down that low that it takes even 5-6 hours with a 25amp charger to recharge a 100amp hour battery you will be replacing your batteries fairly soon ,
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FollowupID: 873000

Reply By: marty d - Sunday, Aug 14, 2016 at 10:12

Sunday, Aug 14, 2016 at 10:12
Normally id be using about 50Ah a day , on a bigger outback trip id be probably double that ( Extra fridge ). Quite often I drive 500-1000 km a day so I could switch the charger from one battery to another halfway , I thought doing it together would just save me mucking about ! , cheers.
AnswerID: 603377

Follow Up By: Allan B (Member, SunCoast) - Sunday, Aug 14, 2016 at 10:22

Sunday, Aug 14, 2016 at 10:22
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Marty, switching your charger from "one battery to another" will be no advantage to the overall charge time. More convenient to charge them both together. If one battery has a greater need of charge then it will take a larger share and they will eventually equalise.
Cheers
Allan

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